[v2] selinux: cache the SID -> context string translation

Message ID	20191106082634.5173-1-omosnace@redhat.com (mailing list archive)
State	Superseded
Headers	show Return-Path: <SRS0=VC3m=Y6=vger.kernel.org=selinux-owner@kernel.org> From: Ondrej Mosnacek <omosnace@redhat.com> To: selinux@vger.kernel.org, Paul Moore <paul@paul-moore.com> Cc: Stephen Smalley <sds@tycho.nsa.gov>, Michal Sekletar <msekleta@redhat.com> Subject: [PATCH v2] selinux: cache the SID -> context string translation Date: Wed, 6 Nov 2019 09:26:34 +0100 Message-Id: <20191106082634.5173-1-omosnace@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: selinux-owner@vger.kernel.org Precedence: bulk
Series	[v2] selinux: cache the SID -> context string translation \| expand [v2] selinux: cache the SID -> context string translation

Ondrej Mosnacek Nov. 6, 2019, 8:26 a.m. UTC

Translating a context struct to string can be quite slow, especially if
the context has a lot of category bits set. This can cause quite
noticeable performance impact in situations where the translation needs
to be done repeatedly. A common example is a UNIX datagram socket with
the SO_PASSSEC option enabled, which is used e.g. by systemd-journald
when receiving log messages via datagram socket. This scenario can be
reproduced with:

    cat /dev/urandom | base64 | logger &
    timeout 30s perf record -p $(pidof systemd-journald) -a -g
    kill %1
    perf report -g none --pretty raw | grep security_secid_to_secctx

Before the caching introduced by this patch, computing the context
string (security_secid_to_secctx() function) takes up ~65% of
systemd-journald's CPU time (assuming a context with 1024 categories
set and Fedora x86_64 release kernel configs). After this patch
(assuming near-perfect cache hit ratio) this overhead is reduced to just
~2%.

This patch addresses the issue by caching a certain number (compile-time
configurable) of recently used context strings to speed up repeated
translations of the same context, while using only a small amount of
memory.

The cache is integrated into the existing sidtab table by adding a field
to each entry, which when not NULL contains an RCU-protected pointer to
a cache entry containing the cached string. The cache entries are kept
in a linked list sorted according to how recently they were used. On a
cache miss when the cache is full, the least recently used entry is
removed to make space for the new entry.

The patch migrates security_sid_to_context_core() to use the cache (also
a few other functions where it was possible without too much fuss, but
these mostly use the translation for logging in case of error, which is
rare).

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1733259
Cc: Michal Sekletar <msekleta@redhat.com>
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
---
 security/selinux/Kconfig       |  11 ++
 security/selinux/ss/services.c | 138 +++++++++++++++----------
 security/selinux/ss/sidtab.c   | 178 +++++++++++++++++++++++++++------
 security/selinux/ss/sidtab.h   |  58 +++++++++--
 4 files changed, 293 insertions(+), 92 deletions(-)

Changes in v2:
 - skip sidtab_sid2str_put() when in non-task context to prevent
   deadlock while avoiding the need to lock the spinlock with
   irqsave/-restore (which is slower)

Stephen Smalley Nov. 6, 2019, 4:11 p.m. UTC | #1

On 11/6/19 3:26 AM, Ondrej Mosnacek wrote:
> Translating a context struct to string can be quite slow, especially if
> the context has a lot of category bits set. This can cause quite
> noticeable performance impact in situations where the translation needs
> to be done repeatedly. A common example is a UNIX datagram socket with
> the SO_PASSSEC option enabled, which is used e.g. by systemd-journald
> when receiving log messages via datagram socket. This scenario can be
> reproduced with:
> 
>      cat /dev/urandom | base64 | logger &
>      timeout 30s perf record -p $(pidof systemd-journald) -a -g
>      kill %1
>      perf report -g none --pretty raw | grep security_secid_to_secctx
> 
> Before the caching introduced by this patch, computing the context
> string (security_secid_to_secctx() function) takes up ~65% of
> systemd-journald's CPU time (assuming a context with 1024 categories
> set and Fedora x86_64 release kernel configs). After this patch
> (assuming near-perfect cache hit ratio) this overhead is reduced to just
> ~2%.
> 
> This patch addresses the issue by caching a certain number (compile-time
> configurable) of recently used context strings to speed up repeated
> translations of the same context, while using only a small amount of
> memory.
> 
> The cache is integrated into the existing sidtab table by adding a field
> to each entry, which when not NULL contains an RCU-protected pointer to
> a cache entry containing the cached string. The cache entries are kept
> in a linked list sorted according to how recently they were used. On a
> cache miss when the cache is full, the least recently used entry is
> removed to make space for the new entry.
> 
> The patch migrates security_sid_to_context_core() to use the cache (also
> a few other functions where it was possible without too much fuss, but
> these mostly use the translation for logging in case of error, which is
> rare).
> 
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1733259
> Cc: Michal Sekletar <msekleta@redhat.com>
> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>

This looks good to me and didn't trigger any issues during testing. 
Might want to run it by the RCU wizards, e.g. Paul McKenney, to confirm 
that it is correct and optimal usage of RCU.  I didn't see anywhere near 
the same degree of performance improvement in running your reproducer 
above but I also have all the kernel debugging options enabled so 
perhaps those are creating noise or perhaps the reproducer doesn't yield 
stable results.  Regardless, you can add:

Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
Tested-by: Stephen Smalley <sds@tycho.nsa.gov>

> ---
>   security/selinux/Kconfig       |  11 ++
>   security/selinux/ss/services.c | 138 +++++++++++++++----------
>   security/selinux/ss/sidtab.c   | 178 +++++++++++++++++++++++++++------
>   security/selinux/ss/sidtab.h   |  58 +++++++++--
>   4 files changed, 293 insertions(+), 92 deletions(-)
> 
> Changes in v2:
>   - skip sidtab_sid2str_put() when in non-task context to prevent
>     deadlock while avoiding the need to lock the spinlock with
>     irqsave/-restore (which is slower)
> 
> diff --git a/security/selinux/Kconfig b/security/selinux/Kconfig
> index 5711689deb6a..35fe8878cf1c 100644
> --- a/security/selinux/Kconfig
> +++ b/security/selinux/Kconfig
> @@ -85,3 +85,14 @@ config SECURITY_SELINUX_CHECKREQPROT_VALUE
>   	  via /selinux/checkreqprot if authorized by policy.
>   
>   	  If you are unsure how to answer this question, answer 0.
> +
> +config SECURITY_SELINUX_SID2STR_CACHE_SIZE
> +	int "NSA SELinux SID to context string translation cache size"
> +	depends on SECURITY_SELINUX
> +	default 256
> +	help
> +	  This option defines the size of the internal SID -> context string
> +	  cache, which improves the performance of context to string
> +	  conversion.  Setting this option to 0 disables the cache completely.
> +
> +	  If unsure, keep the default value.
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index 3a29e7c24ba9..b6dda5261166 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -91,6 +91,12 @@ static int context_struct_to_string(struct policydb *policydb,
>   				    char **scontext,
>   				    u32 *scontext_len);
>   
> +static int sidtab_entry_to_string(struct policydb *policydb,
> +				  struct sidtab *sidtab,
> +				  struct sidtab_entry *entry,
> +				  char **scontext,
> +				  u32 *scontext_len);
> +
>   static void context_struct_compute_av(struct policydb *policydb,
>   				      struct context *scontext,
>   				      struct context *tcontext,
> @@ -716,20 +722,21 @@ static void context_struct_compute_av(struct policydb *policydb,
>   }
>   
>   static int security_validtrans_handle_fail(struct selinux_state *state,
> -					   struct context *ocontext,
> -					   struct context *ncontext,
> -					   struct context *tcontext,
> +					   struct sidtab_entry *oentry,
> +					   struct sidtab_entry *nentry,
> +					   struct sidtab_entry *tentry,
>   					   u16 tclass)
>   {
>   	struct policydb *p = &state->ss->policydb;
> +	struct sidtab *sidtab = state->ss->sidtab;
>   	char *o = NULL, *n = NULL, *t = NULL;
>   	u32 olen, nlen, tlen;
>   
> -	if (context_struct_to_string(p, ocontext, &o, &olen))
> +	if (sidtab_entry_to_string(p, sidtab, oentry, &o, &olen))
>   		goto out;
> -	if (context_struct_to_string(p, ncontext, &n, &nlen))
> +	if (sidtab_entry_to_string(p, sidtab, nentry, &n, &nlen))
>   		goto out;
> -	if (context_struct_to_string(p, tcontext, &t, &tlen))
> +	if (sidtab_entry_to_string(p, sidtab, tentry, &t, &tlen))
>   		goto out;
>   	audit_log(audit_context(), GFP_ATOMIC, AUDIT_SELINUX_ERR,
>   		  "op=security_validate_transition seresult=denied"
> @@ -751,9 +758,9 @@ static int security_compute_validatetrans(struct selinux_state *state,
>   {
>   	struct policydb *policydb;
>   	struct sidtab *sidtab;
> -	struct context *ocontext;
> -	struct context *ncontext;
> -	struct context *tcontext;
> +	struct sidtab_entry *oentry;
> +	struct sidtab_entry *nentry;
> +	struct sidtab_entry *tentry;
>   	struct class_datum *tclass_datum;
>   	struct constraint_node *constraint;
>   	u16 tclass;
> @@ -779,24 +786,24 @@ static int security_compute_validatetrans(struct selinux_state *state,
>   	}
>   	tclass_datum = policydb->class_val_to_struct[tclass - 1];
>   
> -	ocontext = sidtab_search(sidtab, oldsid);
> -	if (!ocontext) {
> +	oentry = sidtab_search_entry(sidtab, oldsid);
> +	if (!oentry) {
>   		pr_err("SELinux: %s:  unrecognized SID %d\n",
>   			__func__, oldsid);
>   		rc = -EINVAL;
>   		goto out;
>   	}
>   
> -	ncontext = sidtab_search(sidtab, newsid);
> -	if (!ncontext) {
> +	nentry = sidtab_search_entry(sidtab, newsid);
> +	if (!nentry) {
>   		pr_err("SELinux: %s:  unrecognized SID %d\n",
>   			__func__, newsid);
>   		rc = -EINVAL;
>   		goto out;
>   	}
>   
> -	tcontext = sidtab_search(sidtab, tasksid);
> -	if (!tcontext) {
> +	tentry = sidtab_search_entry(sidtab, tasksid);
> +	if (!tentry) {
>   		pr_err("SELinux: %s:  unrecognized SID %d\n",
>   			__func__, tasksid);
>   		rc = -EINVAL;
> @@ -805,15 +812,16 @@ static int security_compute_validatetrans(struct selinux_state *state,
>   
>   	constraint = tclass_datum->validatetrans;
>   	while (constraint) {
> -		if (!constraint_expr_eval(policydb, ocontext, ncontext,
> -					  tcontext, constraint->expr)) {
> +		if (!constraint_expr_eval(policydb, &oentry->context,
> +					  &nentry->context, &tentry->context,
> +					  constraint->expr)) {
>   			if (user)
>   				rc = -EPERM;
>   			else
>   				rc = security_validtrans_handle_fail(state,
> -								     ocontext,
> -								     ncontext,
> -								     tcontext,
> +								     oentry,
> +								     nentry,
> +								     tentry,
>   								     tclass);
>   			goto out;
>   		}
> @@ -855,7 +863,7 @@ int security_bounded_transition(struct selinux_state *state,
>   {
>   	struct policydb *policydb;
>   	struct sidtab *sidtab;
> -	struct context *old_context, *new_context;
> +	struct sidtab_entry *old_entry, *new_entry;
>   	struct type_datum *type;
>   	int index;
>   	int rc;
> @@ -869,16 +877,16 @@ int security_bounded_transition(struct selinux_state *state,
>   	sidtab = state->ss->sidtab;
>   
>   	rc = -EINVAL;
> -	old_context = sidtab_search(sidtab, old_sid);
> -	if (!old_context) {
> +	old_entry = sidtab_search_entry(sidtab, old_sid);
> +	if (!old_entry) {
>   		pr_err("SELinux: %s: unrecognized SID %u\n",
>   		       __func__, old_sid);
>   		goto out;
>   	}
>   
>   	rc = -EINVAL;
> -	new_context = sidtab_search(sidtab, new_sid);
> -	if (!new_context) {
> +	new_entry = sidtab_search_entry(sidtab, new_sid);
> +	if (!new_entry) {
>   		pr_err("SELinux: %s: unrecognized SID %u\n",
>   		       __func__, new_sid);
>   		goto out;
> @@ -886,10 +894,10 @@ int security_bounded_transition(struct selinux_state *state,
>   
>   	rc = 0;
>   	/* type/domain unchanged */
> -	if (old_context->type == new_context->type)
> +	if (old_entry->context.type == new_entry->context.type)
>   		goto out;
>   
> -	index = new_context->type;
> +	index = new_entry->context.type;
>   	while (true) {
>   		type = policydb->type_val_to_struct[index - 1];
>   		BUG_ON(!type);
> @@ -901,7 +909,7 @@ int security_bounded_transition(struct selinux_state *state,
>   
>   		/* @newsid is bounded by @oldsid */
>   		rc = 0;
> -		if (type->bounds == old_context->type)
> +		if (type->bounds == old_entry->context.type)
>   			break;
>   
>   		index = type->bounds;
> @@ -912,10 +920,10 @@ int security_bounded_transition(struct selinux_state *state,
>   		char *new_name = NULL;
>   		u32 length;
>   
> -		if (!context_struct_to_string(policydb, old_context,
> -					      &old_name, &length) &&
> -		    !context_struct_to_string(policydb, new_context,
> -					      &new_name, &length)) {
> +		if (!sidtab_entry_to_string(policydb, sidtab, old_entry,
> +					    &old_name, &length) &&
> +		    !sidtab_entry_to_string(policydb, sidtab, new_entry,
> +					    &new_name, &length)) {
>   			audit_log(audit_context(),
>   				  GFP_ATOMIC, AUDIT_SELINUX_ERR,
>   				  "op=security_bounded_transition "
> @@ -1255,6 +1263,23 @@ static int context_struct_to_string(struct policydb *p,
>   	return 0;
>   }
>   
> +static int sidtab_entry_to_string(struct policydb *p,
> +				  struct sidtab *sidtab,
> +				  struct sidtab_entry *entry,
> +				  char **scontext, u32 *scontext_len)
> +{
> +	int rc = sidtab_sid2str_get(sidtab, entry, scontext, scontext_len);
> +
> +	if (rc != -ENOENT)
> +		return rc;
> +
> +	rc = context_struct_to_string(p, &entry->context, scontext,
> +				      scontext_len);
> +	if (!rc && scontext)
> +		sidtab_sid2str_put(sidtab, entry, *scontext, *scontext_len);
> +	return rc;
> +}
> +
>   #include "initial_sid_to_string.h"
>   
>   const char *security_get_initial_sid_context(u32 sid)
> @@ -1271,7 +1296,7 @@ static int security_sid_to_context_core(struct selinux_state *state,
>   {
>   	struct policydb *policydb;
>   	struct sidtab *sidtab;
> -	struct context *context;
> +	struct sidtab_entry *entry;
>   	int rc = 0;
>   
>   	if (scontext)
> @@ -1302,21 +1327,23 @@ static int security_sid_to_context_core(struct selinux_state *state,
>   	read_lock(&state->ss->policy_rwlock);
>   	policydb = &state->ss->policydb;
>   	sidtab = state->ss->sidtab;
> +
>   	if (force)
> -		context = sidtab_search_force(sidtab, sid);
> +		entry = sidtab_search_entry_force(sidtab, sid);
>   	else
> -		context = sidtab_search(sidtab, sid);
> -	if (!context) {
> +		entry = sidtab_search_entry(sidtab, sid);
> +	if (!entry) {
>   		pr_err("SELinux: %s:  unrecognized SID %d\n",
>   			__func__, sid);
>   		rc = -EINVAL;
>   		goto out_unlock;
>   	}
> -	if (only_invalid && !context->len)
> -		rc = 0;
> -	else
> -		rc = context_struct_to_string(policydb, context, scontext,
> -					      scontext_len);
> +	if (only_invalid && !entry->context.len)
> +		goto out_unlock;
> +
> +	rc = sidtab_entry_to_string(policydb, sidtab, entry, scontext,
> +				    scontext_len);
> +
>   out_unlock:
>   	read_unlock(&state->ss->policy_rwlock);
>   out:
> @@ -1574,19 +1601,20 @@ int security_context_to_sid_force(struct selinux_state *state,
>   
>   static int compute_sid_handle_invalid_context(
>   	struct selinux_state *state,
> -	struct context *scontext,
> -	struct context *tcontext,
> +	struct sidtab_entry *sentry,
> +	struct sidtab_entry *tentry,
>   	u16 tclass,
>   	struct context *newcontext)
>   {
>   	struct policydb *policydb = &state->ss->policydb;
> +	struct sidtab *sidtab = state->ss->sidtab;
>   	char *s = NULL, *t = NULL, *n = NULL;
>   	u32 slen, tlen, nlen;
>   	struct audit_buffer *ab;
>   
> -	if (context_struct_to_string(policydb, scontext, &s, &slen))
> +	if (sidtab_entry_to_string(policydb, sidtab, sentry, &s, &slen))
>   		goto out;
> -	if (context_struct_to_string(policydb, tcontext, &t, &tlen))
> +	if (sidtab_entry_to_string(policydb, sidtab, tentry, &t, &tlen))
>   		goto out;
>   	if (context_struct_to_string(policydb, newcontext, &n, &nlen))
>   		goto out;
> @@ -1645,7 +1673,8 @@ static int security_compute_sid(struct selinux_state *state,
>   	struct policydb *policydb;
>   	struct sidtab *sidtab;
>   	struct class_datum *cladatum = NULL;
> -	struct context *scontext = NULL, *tcontext = NULL, newcontext;
> +	struct context *scontext, *tcontext, newcontext;
> +	struct sidtab_entry *sentry, *tentry;
>   	struct role_trans *roletr = NULL;
>   	struct avtab_key avkey;
>   	struct avtab_datum *avdatum;
> @@ -1682,21 +1711,24 @@ static int security_compute_sid(struct selinux_state *state,
>   	policydb = &state->ss->policydb;
>   	sidtab = state->ss->sidtab;
>   
> -	scontext = sidtab_search(sidtab, ssid);
> -	if (!scontext) {
> +	sentry = sidtab_search_entry(sidtab, ssid);
> +	if (!sentry) {
>   		pr_err("SELinux: %s:  unrecognized SID %d\n",
>   		       __func__, ssid);
>   		rc = -EINVAL;
>   		goto out_unlock;
>   	}
> -	tcontext = sidtab_search(sidtab, tsid);
> -	if (!tcontext) {
> +	tentry = sidtab_search_entry(sidtab, tsid);
> +	if (!tentry) {
>   		pr_err("SELinux: %s:  unrecognized SID %d\n",
>   		       __func__, tsid);
>   		rc = -EINVAL;
>   		goto out_unlock;
>   	}
>   
> +	scontext = &sentry->context;
> +	tcontext = &tentry->context;
> +
>   	if (tclass && tclass <= policydb->p_classes.nprim)
>   		cladatum = policydb->class_val_to_struct[tclass - 1];
>   
> @@ -1797,10 +1829,8 @@ static int security_compute_sid(struct selinux_state *state,
>   
>   	/* Check the validity of the context. */
>   	if (!policydb_context_isvalid(policydb, &newcontext)) {
> -		rc = compute_sid_handle_invalid_context(state, scontext,
> -							tcontext,
> -							tclass,
> -							&newcontext);
> +		rc = compute_sid_handle_invalid_context(state, sentry, tentry,
> +							tclass, &newcontext);
>   		if (rc)
>   			goto out_unlock;
>   	}
> diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
> index 7d49994e8d5f..6210d7ff3e31 100644
> --- a/security/selinux/ss/sidtab.c
> +++ b/security/selinux/ss/sidtab.c
> @@ -9,6 +9,8 @@
>    */
>   #include <linux/errno.h>
>   #include <linux/kernel.h>
> +#include <linux/list.h>
> +#include <linux/rcupdate.h>
>   #include <linux/slab.h>
>   #include <linux/sched.h>
>   #include <linux/spinlock.h>
> @@ -17,6 +19,14 @@
>   #include "security.h"
>   #include "sidtab.h"
>   
> +struct sidtab_str_cache {
> +	struct rcu_head rcu_member;
> +	struct list_head lru_member;
> +	struct sidtab_entry *parent;
> +	u32 len;
> +	char str[];
> +};
> +
>   int sidtab_init(struct sidtab *s)
>   {
>   	u32 i;
> @@ -34,24 +44,33 @@ int sidtab_init(struct sidtab *s)
>   	s->convert = NULL;
>   
>   	spin_lock_init(&s->lock);
> +
> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
> +	s->cache_free_slots = CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE;
> +	INIT_LIST_HEAD(&s->cache_lru_list);
> +	spin_lock_init(&s->cache_lock);
> +#endif
>   	return 0;
>   }
>   
>   int sidtab_set_initial(struct sidtab *s, u32 sid, struct context *context)
>   {
> -	struct sidtab_isid_entry *entry;
> +	struct sidtab_isid_entry *isid;
>   	int rc;
>   
>   	if (sid == 0 || sid > SECINITSID_NUM)
>   		return -EINVAL;
>   
> -	entry = &s->isids[sid - 1];
> +	isid = &s->isids[sid - 1];
>   
> -	rc = context_cpy(&entry->context, context);
> +	rc = context_cpy(&isid->entry.context, context);
>   	if (rc)
>   		return rc;
>   
> -	entry->set = 1;
> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
> +	isid->entry.cache = NULL;
> +#endif
> +	isid->set = 1;
>   	return 0;
>   }
>   
> @@ -88,7 +107,8 @@ static int sidtab_alloc_roots(struct sidtab *s, u32 level)
>   	return 0;
>   }
>   
> -static struct context *sidtab_do_lookup(struct sidtab *s, u32 index, int alloc)
> +static struct sidtab_entry *sidtab_do_lookup(struct sidtab *s, u32 index,
> +					     int alloc)
>   {
>   	union sidtab_entry_inner *entry;
>   	u32 level, capacity_shift, leaf_index = index / SIDTAB_LEAF_ENTRIES;
> @@ -125,10 +145,16 @@ static struct context *sidtab_do_lookup(struct sidtab *s, u32 index, int alloc)
>   		if (!entry->ptr_leaf)
>   			return NULL;
>   	}
> -	return &entry->ptr_leaf->entries[index % SIDTAB_LEAF_ENTRIES].context;
> +	return &entry->ptr_leaf->entries[index % SIDTAB_LEAF_ENTRIES];
> +}
> +
> +/* use when you know that there is enough entries */
> +static struct context *sidtab_lookup_unsafe(struct sidtab *s, u32 index)
> +{
> +	return &sidtab_do_lookup(s, index, 0)->context;
>   }
>   
> -static struct context *sidtab_lookup(struct sidtab *s, u32 index)
> +static struct sidtab_entry *sidtab_lookup(struct sidtab *s, u32 index)
>   {
>   	/* read entries only after reading count */
>   	u32 count = smp_load_acquire(&s->count);
> @@ -139,33 +165,34 @@ static struct context *sidtab_lookup(struct sidtab *s, u32 index)
>   	return sidtab_do_lookup(s, index, 0);
>   }
>   
> -static struct context *sidtab_lookup_initial(struct sidtab *s, u32 sid)
> +static struct sidtab_entry *sidtab_lookup_initial(struct sidtab *s, u32 sid)
>   {
> -	return s->isids[sid - 1].set ? &s->isids[sid - 1].context : NULL;
> +	return s->isids[sid - 1].set ? &s->isids[sid - 1].entry : NULL;
>   }
>   
> -static struct context *sidtab_search_core(struct sidtab *s, u32 sid, int force)
> +static struct sidtab_entry *sidtab_search_core(struct sidtab *s, u32 sid,
> +					       int force)
>   {
> -	struct context *context;
> -
>   	if (sid != 0) {
> +		struct sidtab_entry *entry;
> +
>   		if (sid > SECINITSID_NUM)
> -			context = sidtab_lookup(s, sid - (SECINITSID_NUM + 1));
> +			entry = sidtab_lookup(s, sid - (SECINITSID_NUM + 1));
>   		else
> -			context = sidtab_lookup_initial(s, sid);
> -		if (context && (!context->len || force))
> -			return context;
> +			entry = sidtab_lookup_initial(s, sid);
> +		if (entry && (!entry->context.len || force))
> +			return entry;
>   	}
>   
>   	return sidtab_lookup_initial(s, SECINITSID_UNLABELED);
>   }
>   
> -struct context *sidtab_search(struct sidtab *s, u32 sid)
> +struct sidtab_entry *sidtab_search_entry(struct sidtab *s, u32 sid)
>   {
>   	return sidtab_search_core(s, sid, 0);
>   }
>   
> -struct context *sidtab_search_force(struct sidtab *s, u32 sid)
> +struct sidtab_entry *sidtab_search_entry_force(struct sidtab *s, u32 sid)
>   {
>   	return sidtab_search_core(s, sid, 1);
>   }
> @@ -230,7 +257,7 @@ static int sidtab_rcache_search(struct sidtab *s, struct context *context,
>   		if (v >= SIDTAB_MAX)
>   			continue;
>   
> -		if (context_cmp(sidtab_do_lookup(s, v, 0), context)) {
> +		if (context_cmp(sidtab_lookup_unsafe(s, v), context)) {
>   			sidtab_rcache_update(s, v, i);
>   			*index = v;
>   			return 0;
> @@ -245,7 +272,7 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
>   	unsigned long flags;
>   	u32 count, count_locked, level, pos;
>   	struct sidtab_convert_params *convert;
> -	struct context *dst, *dst_convert;
> +	struct sidtab_entry *dst, *dst_convert;
>   	int rc;
>   
>   	rc = sidtab_rcache_search(s, context, index);
> @@ -273,7 +300,7 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
>   
>   	/* if count has changed before we acquired the lock, then catch up */
>   	while (count < count_locked) {
> -		if (context_cmp(sidtab_do_lookup(s, count, 0), context)) {
> +		if (context_cmp(sidtab_lookup_unsafe(s, count), context)) {
>   			sidtab_rcache_push(s, count);
>   			*index = count;
>   			rc = 0;
> @@ -293,7 +320,7 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
>   	if (!dst)
>   		goto out_unlock;
>   
> -	rc = context_cpy(dst, context);
> +	rc = context_cpy(&dst->context, context);
>   	if (rc)
>   		goto out_unlock;
>   
> @@ -305,13 +332,14 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
>   		rc = -ENOMEM;
>   		dst_convert = sidtab_do_lookup(convert->target, count, 1);
>   		if (!dst_convert) {
> -			context_destroy(dst);
> +			context_destroy(&dst->context);
>   			goto out_unlock;
>   		}
>   
> -		rc = convert->func(context, dst_convert, convert->args);
> +		rc = convert->func(context, &dst_convert->context,
> +				   convert->args);
>   		if (rc) {
> -			context_destroy(dst);
> +			context_destroy(&dst->context);
>   			goto out_unlock;
>   		}
>   
> @@ -341,9 +369,9 @@ int sidtab_context_to_sid(struct sidtab *s, struct context *context, u32 *sid)
>   	u32 i;
>   
>   	for (i = 0; i < SECINITSID_NUM; i++) {
> -		struct sidtab_isid_entry *entry = &s->isids[i];
> +		struct sidtab_isid_entry *isid = &s->isids[i];
>   
> -		if (entry->set && context_cmp(context, &entry->context)) {
> +		if (isid->set && context_cmp(context, &isid->entry.context)) {
>   			*sid = i + 1;
>   			return 0;
>   		}
> @@ -453,6 +481,14 @@ int sidtab_convert(struct sidtab *s, struct sidtab_convert_params *params)
>   	return rc;
>   }
>   
> +static void sidtab_destroy_entry(struct sidtab_entry *entry)
> +{
> +	context_destroy(&entry->context);
> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
> +	kfree(entry->cache);
> +#endif
> +}
> +
>   static void sidtab_destroy_tree(union sidtab_entry_inner entry, u32 level)
>   {
>   	u32 i;
> @@ -473,7 +509,7 @@ static void sidtab_destroy_tree(union sidtab_entry_inner entry, u32 level)
>   			return;
>   
>   		for (i = 0; i < SIDTAB_LEAF_ENTRIES; i++)
> -			context_destroy(&node->entries[i].context);
> +			sidtab_destroy_entry(&node->entries[i]);
>   		kfree(node);
>   	}
>   }
> @@ -484,7 +520,7 @@ void sidtab_destroy(struct sidtab *s)
>   
>   	for (i = 0; i < SECINITSID_NUM; i++)
>   		if (s->isids[i].set)
> -			context_destroy(&s->isids[i].context);
> +			sidtab_destroy_entry(&s->isids[i].entry);
>   
>   	level = SIDTAB_MAX_LEVEL;
>   	while (level && !s->roots[level].ptr_inner)
> @@ -492,3 +528,87 @@ void sidtab_destroy(struct sidtab *s)
>   
>   	sidtab_destroy_tree(s->roots[level], level);
>   }
> +
> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
> +
> +void sidtab_sid2str_put(struct sidtab *s, struct sidtab_entry *entry,
> +			const char *str, u32 str_len)
> +{
> +	struct sidtab_str_cache *cache, *victim;
> +
> +	/* do not cache invalid contexts */
> +	if (entry->context.len)
> +		return;
> +
> +	/*
> +	 * Skip the put operation when in non-task context to avoid the need
> +	 * to disable interrupts while holding s->cache_lock.
> +	 */
> +	if (!in_task())
> +		return;
> +
> +	spin_lock(&s->cache_lock);
> +
> +	if (entry->cache) {
> +		/* entry in cache - just bump to he head of LRU list */
> +		list_move(&entry->cache->lru_member, &s->cache_lru_list);
> +		goto out_unlock;
> +	}
> +
> +	cache = kmalloc(sizeof(struct sidtab_str_cache) + str_len, GFP_ATOMIC);
> +	if (!cache)
> +		goto out_unlock;
> +
> +	if (s->cache_free_slots == 0) {
> +		/* pop a cache entry from the tail and free it */
> +		victim = container_of(s->cache_lru_list.prev,
> +				      struct sidtab_str_cache, lru_member);
> +		list_del(&victim->lru_member);
> +		kfree_rcu(victim, rcu_member);
> +		rcu_assign_pointer(victim->parent->cache, NULL);
> +	} else {
> +		s->cache_free_slots--;
> +	}
> +	cache->parent = entry;
> +	cache->len = str_len;
> +	memcpy(cache->str, str, str_len);
> +	rcu_head_init(&cache->rcu_member);
> +	list_add(&cache->lru_member, &s->cache_lru_list);
> +
> +	rcu_assign_pointer(entry->cache, cache);
> +
> +out_unlock:
> +	spin_unlock(&s->cache_lock);
> +}
> +
> +int sidtab_sid2str_get(struct sidtab *s, struct sidtab_entry *entry,
> +		       char **out, u32 *out_len)
> +{
> +	struct sidtab_str_cache *cache;
> +	int rc = 0;
> +
> +	if (entry->context.len)
> +		return -ENOENT; /* do not cache invalid contexts */
> +
> +	rcu_read_lock();
> +
> +	cache = rcu_dereference(entry->cache);
> +	if (!cache) {
> +		rc = -ENOENT;
> +	} else {
> +		*out_len = cache->len;
> +		if (out) {
> +			*out = kmemdup(cache->str, cache->len, GFP_ATOMIC);
> +			if (!*out)
> +				rc = -ENOMEM;
> +		}
> +	}
> +
> +	rcu_read_unlock();
> +
> +	if (!rc && out)
> +		sidtab_sid2str_put(s, entry, *out, *out_len);
> +	return rc;
> +}
> +
> +#endif /* CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0 */
> diff --git a/security/selinux/ss/sidtab.h b/security/selinux/ss/sidtab.h
> index 1f4763141aa1..9159a300bde3 100644
> --- a/security/selinux/ss/sidtab.h
> +++ b/security/selinux/ss/sidtab.h
> @@ -16,13 +16,13 @@
>   
>   #include "context.h"
>   
> -struct sidtab_entry_leaf {
> +struct sidtab_entry {
>   	struct context context;
> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
> +	struct sidtab_str_cache *cache;
> +#endif
>   };
>   
> -struct sidtab_node_inner;
> -struct sidtab_node_leaf;
> -
>   union sidtab_entry_inner {
>   	struct sidtab_node_inner *ptr_inner;
>   	struct sidtab_node_leaf  *ptr_leaf;
> @@ -38,7 +38,7 @@ union sidtab_entry_inner {
>   	(SIDTAB_NODE_ALLOC_SHIFT - size_to_shift(sizeof(union sidtab_entry_inner)))
>   #define SIDTAB_INNER_ENTRIES ((size_t)1 << SIDTAB_INNER_SHIFT)
>   #define SIDTAB_LEAF_ENTRIES \
> -	(SIDTAB_NODE_ALLOC_SIZE / sizeof(struct sidtab_entry_leaf))
> +	(SIDTAB_NODE_ALLOC_SIZE / sizeof(struct sidtab_entry))
>   
>   #define SIDTAB_MAX_BITS 32
>   #define SIDTAB_MAX U32_MAX
> @@ -48,7 +48,7 @@ union sidtab_entry_inner {
>   		     SIDTAB_INNER_SHIFT)
>   
>   struct sidtab_node_leaf {
> -	struct sidtab_entry_leaf entries[SIDTAB_LEAF_ENTRIES];
> +	struct sidtab_entry entries[SIDTAB_LEAF_ENTRIES];
>   };
>   
>   struct sidtab_node_inner {
> @@ -57,7 +57,7 @@ struct sidtab_node_inner {
>   
>   struct sidtab_isid_entry {
>   	int set;
> -	struct context context;
> +	struct sidtab_entry entry;
>   };
>   
>   struct sidtab_convert_params {
> @@ -83,6 +83,13 @@ struct sidtab {
>   	struct sidtab_convert_params *convert;
>   	spinlock_t lock;
>   
> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
> +	/* SID -> context string cache */
> +	u32 cache_free_slots;
> +	struct list_head cache_lru_list;
> +	spinlock_t cache_lock;
> +#endif
> +
>   	/* reverse lookup cache - access atomically via {READ|WRITE}_ONCE() */
>   	u32 rcache[SIDTAB_RCACHE_SIZE];
>   
> @@ -92,8 +99,22 @@ struct sidtab {
>   
>   int sidtab_init(struct sidtab *s);
>   int sidtab_set_initial(struct sidtab *s, u32 sid, struct context *context);
> -struct context *sidtab_search(struct sidtab *s, u32 sid);
> -struct context *sidtab_search_force(struct sidtab *s, u32 sid);
> +struct sidtab_entry *sidtab_search_entry(struct sidtab *s, u32 sid);
> +struct sidtab_entry *sidtab_search_entry_force(struct sidtab *s, u32 sid);
> +
> +static inline struct context *sidtab_search(struct sidtab *s, u32 sid)
> +{
> +	struct sidtab_entry *entry = sidtab_search_entry(s, sid);
> +
> +	return entry ? &entry->context : NULL;
> +}
> +
> +static inline struct context *sidtab_search_force(struct sidtab *s, u32 sid)
> +{
> +	struct sidtab_entry *entry = sidtab_search_entry_force(s, sid);
> +
> +	return entry ? &entry->context : NULL;
> +}
>   
>   int sidtab_convert(struct sidtab *s, struct sidtab_convert_params *params);
>   
> @@ -101,6 +122,25 @@ int sidtab_context_to_sid(struct sidtab *s, struct context *context, u32 *sid);
>   
>   void sidtab_destroy(struct sidtab *s);
>   
> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
> +void sidtab_sid2str_put(struct sidtab *s, struct sidtab_entry *entry,
> +			const char *str, u32 str_len);
> +int sidtab_sid2str_get(struct sidtab *s, struct sidtab_entry *entry,
> +		       char **out, u32 *out_len);
> +#else
> +static inline void sidtab_sid2str_put(struct sidtab *s,
> +				      struct sidtab_entry *entry,
> +				      const char *str, u32 str_len)
> +{
> +}
> +static inline int sidtab_sid2str_get(struct sidtab *s,
> +				     struct sidtab_entry *entry,
> +				     char **out, u32 *out_len)
> +{
> +	return -ENOENT;
> +}
> +#endif /* CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0 */
> +
>   #endif	/* _SS_SIDTAB_H_ */
>   
>   
>

Stephen Smalley Nov. 6, 2019, 7:22 p.m. UTC | #2

On 11/6/19 11:11 AM, Stephen Smalley wrote:
> On 11/6/19 3:26 AM, Ondrej Mosnacek wrote:
>> Translating a context struct to string can be quite slow, especially if
>> the context has a lot of category bits set. This can cause quite
>> noticeable performance impact in situations where the translation needs
>> to be done repeatedly. A common example is a UNIX datagram socket with
>> the SO_PASSSEC option enabled, which is used e.g. by systemd-journald
>> when receiving log messages via datagram socket. This scenario can be
>> reproduced with:
>>
>>      cat /dev/urandom | base64 | logger &
>>      timeout 30s perf record -p $(pidof systemd-journald) -a -g
>>      kill %1
>>      perf report -g none --pretty raw | grep security_secid_to_secctx
>>
>> Before the caching introduced by this patch, computing the context
>> string (security_secid_to_secctx() function) takes up ~65% of
>> systemd-journald's CPU time (assuming a context with 1024 categories
>> set and Fedora x86_64 release kernel configs). After this patch
>> (assuming near-perfect cache hit ratio) this overhead is reduced to just
>> ~2%.
>>
>> This patch addresses the issue by caching a certain number (compile-time
>> configurable) of recently used context strings to speed up repeated
>> translations of the same context, while using only a small amount of
>> memory.
>>
>> The cache is integrated into the existing sidtab table by adding a field
>> to each entry, which when not NULL contains an RCU-protected pointer to
>> a cache entry containing the cached string. The cache entries are kept
>> in a linked list sorted according to how recently they were used. On a
>> cache miss when the cache is full, the least recently used entry is
>> removed to make space for the new entry.
>>
>> The patch migrates security_sid_to_context_core() to use the cache (also
>> a few other functions where it was possible without too much fuss, but
>> these mostly use the translation for logging in case of error, which is
>> rare).
>>
>> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1733259
>> Cc: Michal Sekletar <msekleta@redhat.com>
>> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> 
> This looks good to me and didn't trigger any issues during testing. 
> Might want to run it by the RCU wizards, e.g. Paul McKenney, to confirm 
> that it is correct and optimal usage of RCU.  I didn't see anywhere near 
> the same degree of performance improvement in running your reproducer 
> above but I also have all the kernel debugging options enabled so 
> perhaps those are creating noise or perhaps the reproducer doesn't yield 
> stable results.

Rebuilding with the stock Fedora x86_64 kernel config was closer to your 
results albeit still different, ~35% before and ~2% after.

>  Regardless, you can add:
> 
> Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
> Tested-by: Stephen Smalley <sds@tycho.nsa.gov>
> 
>> ---
>>   security/selinux/Kconfig       |  11 ++
>>   security/selinux/ss/services.c | 138 +++++++++++++++----------
>>   security/selinux/ss/sidtab.c   | 178 +++++++++++++++++++++++++++------
>>   security/selinux/ss/sidtab.h   |  58 +++++++++--
>>   4 files changed, 293 insertions(+), 92 deletions(-)
>>
>> Changes in v2:
>>   - skip sidtab_sid2str_put() when in non-task context to prevent
>>     deadlock while avoiding the need to lock the spinlock with
>>     irqsave/-restore (which is slower)
>>
>> diff --git a/security/selinux/Kconfig b/security/selinux/Kconfig
>> index 5711689deb6a..35fe8878cf1c 100644
>> --- a/security/selinux/Kconfig
>> +++ b/security/selinux/Kconfig
>> @@ -85,3 +85,14 @@ config SECURITY_SELINUX_CHECKREQPROT_VALUE
>>         via /selinux/checkreqprot if authorized by policy.
>>         If you are unsure how to answer this question, answer 0.
>> +
>> +config SECURITY_SELINUX_SID2STR_CACHE_SIZE
>> +    int "NSA SELinux SID to context string translation cache size"
>> +    depends on SECURITY_SELINUX
>> +    default 256
>> +    help
>> +      This option defines the size of the internal SID -> context string
>> +      cache, which improves the performance of context to string
>> +      conversion.  Setting this option to 0 disables the cache 
>> completely.
>> +
>> +      If unsure, keep the default value.
>> diff --git a/security/selinux/ss/services.c 
>> b/security/selinux/ss/services.c
>> index 3a29e7c24ba9..b6dda5261166 100644
>> --- a/security/selinux/ss/services.c
>> +++ b/security/selinux/ss/services.c
>> @@ -91,6 +91,12 @@ static int context_struct_to_string(struct policydb 
>> *policydb,
>>                       char **scontext,
>>                       u32 *scontext_len);
>> +static int sidtab_entry_to_string(struct policydb *policydb,
>> +                  struct sidtab *sidtab,
>> +                  struct sidtab_entry *entry,
>> +                  char **scontext,
>> +                  u32 *scontext_len);
>> +
>>   static void context_struct_compute_av(struct policydb *policydb,
>>                         struct context *scontext,
>>                         struct context *tcontext,
>> @@ -716,20 +722,21 @@ static void context_struct_compute_av(struct 
>> policydb *policydb,
>>   }
>>   static int security_validtrans_handle_fail(struct selinux_state *state,
>> -                       struct context *ocontext,
>> -                       struct context *ncontext,
>> -                       struct context *tcontext,
>> +                       struct sidtab_entry *oentry,
>> +                       struct sidtab_entry *nentry,
>> +                       struct sidtab_entry *tentry,
>>                          u16 tclass)
>>   {
>>       struct policydb *p = &state->ss->policydb;
>> +    struct sidtab *sidtab = state->ss->sidtab;
>>       char *o = NULL, *n = NULL, *t = NULL;
>>       u32 olen, nlen, tlen;
>> -    if (context_struct_to_string(p, ocontext, &o, &olen))
>> +    if (sidtab_entry_to_string(p, sidtab, oentry, &o, &olen))
>>           goto out;
>> -    if (context_struct_to_string(p, ncontext, &n, &nlen))
>> +    if (sidtab_entry_to_string(p, sidtab, nentry, &n, &nlen))
>>           goto out;
>> -    if (context_struct_to_string(p, tcontext, &t, &tlen))
>> +    if (sidtab_entry_to_string(p, sidtab, tentry, &t, &tlen))
>>           goto out;
>>       audit_log(audit_context(), GFP_ATOMIC, AUDIT_SELINUX_ERR,
>>             "op=security_validate_transition seresult=denied"
>> @@ -751,9 +758,9 @@ static int security_compute_validatetrans(struct 
>> selinux_state *state,
>>   {
>>       struct policydb *policydb;
>>       struct sidtab *sidtab;
>> -    struct context *ocontext;
>> -    struct context *ncontext;
>> -    struct context *tcontext;
>> +    struct sidtab_entry *oentry;
>> +    struct sidtab_entry *nentry;
>> +    struct sidtab_entry *tentry;
>>       struct class_datum *tclass_datum;
>>       struct constraint_node *constraint;
>>       u16 tclass;
>> @@ -779,24 +786,24 @@ static int security_compute_validatetrans(struct 
>> selinux_state *state,
>>       }
>>       tclass_datum = policydb->class_val_to_struct[tclass - 1];
>> -    ocontext = sidtab_search(sidtab, oldsid);
>> -    if (!ocontext) {
>> +    oentry = sidtab_search_entry(sidtab, oldsid);
>> +    if (!oentry) {
>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>               __func__, oldsid);
>>           rc = -EINVAL;
>>           goto out;
>>       }
>> -    ncontext = sidtab_search(sidtab, newsid);
>> -    if (!ncontext) {
>> +    nentry = sidtab_search_entry(sidtab, newsid);
>> +    if (!nentry) {
>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>               __func__, newsid);
>>           rc = -EINVAL;
>>           goto out;
>>       }
>> -    tcontext = sidtab_search(sidtab, tasksid);
>> -    if (!tcontext) {
>> +    tentry = sidtab_search_entry(sidtab, tasksid);
>> +    if (!tentry) {
>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>               __func__, tasksid);
>>           rc = -EINVAL;
>> @@ -805,15 +812,16 @@ static int security_compute_validatetrans(struct 
>> selinux_state *state,
>>       constraint = tclass_datum->validatetrans;
>>       while (constraint) {
>> -        if (!constraint_expr_eval(policydb, ocontext, ncontext,
>> -                      tcontext, constraint->expr)) {
>> +        if (!constraint_expr_eval(policydb, &oentry->context,
>> +                      &nentry->context, &tentry->context,
>> +                      constraint->expr)) {
>>               if (user)
>>                   rc = -EPERM;
>>               else
>>                   rc = security_validtrans_handle_fail(state,
>> -                                     ocontext,
>> -                                     ncontext,
>> -                                     tcontext,
>> +                                     oentry,
>> +                                     nentry,
>> +                                     tentry,
>>                                        tclass);
>>               goto out;
>>           }
>> @@ -855,7 +863,7 @@ int security_bounded_transition(struct 
>> selinux_state *state,
>>   {
>>       struct policydb *policydb;
>>       struct sidtab *sidtab;
>> -    struct context *old_context, *new_context;
>> +    struct sidtab_entry *old_entry, *new_entry;
>>       struct type_datum *type;
>>       int index;
>>       int rc;
>> @@ -869,16 +877,16 @@ int security_bounded_transition(struct 
>> selinux_state *state,
>>       sidtab = state->ss->sidtab;
>>       rc = -EINVAL;
>> -    old_context = sidtab_search(sidtab, old_sid);
>> -    if (!old_context) {
>> +    old_entry = sidtab_search_entry(sidtab, old_sid);
>> +    if (!old_entry) {
>>           pr_err("SELinux: %s: unrecognized SID %u\n",
>>                  __func__, old_sid);
>>           goto out;
>>       }
>>       rc = -EINVAL;
>> -    new_context = sidtab_search(sidtab, new_sid);
>> -    if (!new_context) {
>> +    new_entry = sidtab_search_entry(sidtab, new_sid);
>> +    if (!new_entry) {
>>           pr_err("SELinux: %s: unrecognized SID %u\n",
>>                  __func__, new_sid);
>>           goto out;
>> @@ -886,10 +894,10 @@ int security_bounded_transition(struct 
>> selinux_state *state,
>>       rc = 0;
>>       /* type/domain unchanged */
>> -    if (old_context->type == new_context->type)
>> +    if (old_entry->context.type == new_entry->context.type)
>>           goto out;
>> -    index = new_context->type;
>> +    index = new_entry->context.type;
>>       while (true) {
>>           type = policydb->type_val_to_struct[index - 1];
>>           BUG_ON(!type);
>> @@ -901,7 +909,7 @@ int security_bounded_transition(struct 
>> selinux_state *state,
>>           /* @newsid is bounded by @oldsid */
>>           rc = 0;
>> -        if (type->bounds == old_context->type)
>> +        if (type->bounds == old_entry->context.type)
>>               break;
>>           index = type->bounds;
>> @@ -912,10 +920,10 @@ int security_bounded_transition(struct 
>> selinux_state *state,
>>           char *new_name = NULL;
>>           u32 length;
>> -        if (!context_struct_to_string(policydb, old_context,
>> -                          &old_name, &length) &&
>> -            !context_struct_to_string(policydb, new_context,
>> -                          &new_name, &length)) {
>> +        if (!sidtab_entry_to_string(policydb, sidtab, old_entry,
>> +                        &old_name, &length) &&
>> +            !sidtab_entry_to_string(policydb, sidtab, new_entry,
>> +                        &new_name, &length)) {
>>               audit_log(audit_context(),
>>                     GFP_ATOMIC, AUDIT_SELINUX_ERR,
>>                     "op=security_bounded_transition "
>> @@ -1255,6 +1263,23 @@ static int context_struct_to_string(struct 
>> policydb *p,
>>       return 0;
>>   }
>> +static int sidtab_entry_to_string(struct policydb *p,
>> +                  struct sidtab *sidtab,
>> +                  struct sidtab_entry *entry,
>> +                  char **scontext, u32 *scontext_len)
>> +{
>> +    int rc = sidtab_sid2str_get(sidtab, entry, scontext, scontext_len);
>> +
>> +    if (rc != -ENOENT)
>> +        return rc;
>> +
>> +    rc = context_struct_to_string(p, &entry->context, scontext,
>> +                      scontext_len);
>> +    if (!rc && scontext)
>> +        sidtab_sid2str_put(sidtab, entry, *scontext, *scontext_len);
>> +    return rc;
>> +}
>> +
>>   #include "initial_sid_to_string.h"
>>   const char *security_get_initial_sid_context(u32 sid)
>> @@ -1271,7 +1296,7 @@ static int security_sid_to_context_core(struct 
>> selinux_state *state,
>>   {
>>       struct policydb *policydb;
>>       struct sidtab *sidtab;
>> -    struct context *context;
>> +    struct sidtab_entry *entry;
>>       int rc = 0;
>>       if (scontext)
>> @@ -1302,21 +1327,23 @@ static int security_sid_to_context_core(struct 
>> selinux_state *state,
>>       read_lock(&state->ss->policy_rwlock);
>>       policydb = &state->ss->policydb;
>>       sidtab = state->ss->sidtab;
>> +
>>       if (force)
>> -        context = sidtab_search_force(sidtab, sid);
>> +        entry = sidtab_search_entry_force(sidtab, sid);
>>       else
>> -        context = sidtab_search(sidtab, sid);
>> -    if (!context) {
>> +        entry = sidtab_search_entry(sidtab, sid);
>> +    if (!entry) {
>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>               __func__, sid);
>>           rc = -EINVAL;
>>           goto out_unlock;
>>       }
>> -    if (only_invalid && !context->len)
>> -        rc = 0;
>> -    else
>> -        rc = context_struct_to_string(policydb, context, scontext,
>> -                          scontext_len);
>> +    if (only_invalid && !entry->context.len)
>> +        goto out_unlock;
>> +
>> +    rc = sidtab_entry_to_string(policydb, sidtab, entry, scontext,
>> +                    scontext_len);
>> +
>>   out_unlock:
>>       read_unlock(&state->ss->policy_rwlock);
>>   out:
>> @@ -1574,19 +1601,20 @@ int security_context_to_sid_force(struct 
>> selinux_state *state,
>>   static int compute_sid_handle_invalid_context(
>>       struct selinux_state *state,
>> -    struct context *scontext,
>> -    struct context *tcontext,
>> +    struct sidtab_entry *sentry,
>> +    struct sidtab_entry *tentry,
>>       u16 tclass,
>>       struct context *newcontext)
>>   {
>>       struct policydb *policydb = &state->ss->policydb;
>> +    struct sidtab *sidtab = state->ss->sidtab;
>>       char *s = NULL, *t = NULL, *n = NULL;
>>       u32 slen, tlen, nlen;
>>       struct audit_buffer *ab;
>> -    if (context_struct_to_string(policydb, scontext, &s, &slen))
>> +    if (sidtab_entry_to_string(policydb, sidtab, sentry, &s, &slen))
>>           goto out;
>> -    if (context_struct_to_string(policydb, tcontext, &t, &tlen))
>> +    if (sidtab_entry_to_string(policydb, sidtab, tentry, &t, &tlen))
>>           goto out;
>>       if (context_struct_to_string(policydb, newcontext, &n, &nlen))
>>           goto out;
>> @@ -1645,7 +1673,8 @@ static int security_compute_sid(struct 
>> selinux_state *state,
>>       struct policydb *policydb;
>>       struct sidtab *sidtab;
>>       struct class_datum *cladatum = NULL;
>> -    struct context *scontext = NULL, *tcontext = NULL, newcontext;
>> +    struct context *scontext, *tcontext, newcontext;
>> +    struct sidtab_entry *sentry, *tentry;
>>       struct role_trans *roletr = NULL;
>>       struct avtab_key avkey;
>>       struct avtab_datum *avdatum;
>> @@ -1682,21 +1711,24 @@ static int security_compute_sid(struct 
>> selinux_state *state,
>>       policydb = &state->ss->policydb;
>>       sidtab = state->ss->sidtab;
>> -    scontext = sidtab_search(sidtab, ssid);
>> -    if (!scontext) {
>> +    sentry = sidtab_search_entry(sidtab, ssid);
>> +    if (!sentry) {
>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>                  __func__, ssid);
>>           rc = -EINVAL;
>>           goto out_unlock;
>>       }
>> -    tcontext = sidtab_search(sidtab, tsid);
>> -    if (!tcontext) {
>> +    tentry = sidtab_search_entry(sidtab, tsid);
>> +    if (!tentry) {
>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>                  __func__, tsid);
>>           rc = -EINVAL;
>>           goto out_unlock;
>>       }
>> +    scontext = &sentry->context;
>> +    tcontext = &tentry->context;
>> +
>>       if (tclass && tclass <= policydb->p_classes.nprim)
>>           cladatum = policydb->class_val_to_struct[tclass - 1];
>> @@ -1797,10 +1829,8 @@ static int security_compute_sid(struct 
>> selinux_state *state,
>>       /* Check the validity of the context. */
>>       if (!policydb_context_isvalid(policydb, &newcontext)) {
>> -        rc = compute_sid_handle_invalid_context(state, scontext,
>> -                            tcontext,
>> -                            tclass,
>> -                            &newcontext);
>> +        rc = compute_sid_handle_invalid_context(state, sentry, tentry,
>> +                            tclass, &newcontext);
>>           if (rc)
>>               goto out_unlock;
>>       }
>> diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
>> index 7d49994e8d5f..6210d7ff3e31 100644
>> --- a/security/selinux/ss/sidtab.c
>> +++ b/security/selinux/ss/sidtab.c
>> @@ -9,6 +9,8 @@
>>    */
>>   #include <linux/errno.h>
>>   #include <linux/kernel.h>
>> +#include <linux/list.h>
>> +#include <linux/rcupdate.h>
>>   #include <linux/slab.h>
>>   #include <linux/sched.h>
>>   #include <linux/spinlock.h>
>> @@ -17,6 +19,14 @@
>>   #include "security.h"
>>   #include "sidtab.h"
>> +struct sidtab_str_cache {
>> +    struct rcu_head rcu_member;
>> +    struct list_head lru_member;
>> +    struct sidtab_entry *parent;
>> +    u32 len;
>> +    char str[];
>> +};
>> +
>>   int sidtab_init(struct sidtab *s)
>>   {
>>       u32 i;
>> @@ -34,24 +44,33 @@ int sidtab_init(struct sidtab *s)
>>       s->convert = NULL;
>>       spin_lock_init(&s->lock);
>> +
>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>> +    s->cache_free_slots = CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE;
>> +    INIT_LIST_HEAD(&s->cache_lru_list);
>> +    spin_lock_init(&s->cache_lock);
>> +#endif
>>       return 0;
>>   }
>>   int sidtab_set_initial(struct sidtab *s, u32 sid, struct context 
>> *context)
>>   {
>> -    struct sidtab_isid_entry *entry;
>> +    struct sidtab_isid_entry *isid;
>>       int rc;
>>       if (sid == 0 || sid > SECINITSID_NUM)
>>           return -EINVAL;
>> -    entry = &s->isids[sid - 1];
>> +    isid = &s->isids[sid - 1];
>> -    rc = context_cpy(&entry->context, context);
>> +    rc = context_cpy(&isid->entry.context, context);
>>       if (rc)
>>           return rc;
>> -    entry->set = 1;
>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>> +    isid->entry.cache = NULL;
>> +#endif
>> +    isid->set = 1;
>>       return 0;
>>   }
>> @@ -88,7 +107,8 @@ static int sidtab_alloc_roots(struct sidtab *s, u32 
>> level)
>>       return 0;
>>   }
>> -static struct context *sidtab_do_lookup(struct sidtab *s, u32 index, 
>> int alloc)
>> +static struct sidtab_entry *sidtab_do_lookup(struct sidtab *s, u32 
>> index,
>> +                         int alloc)
>>   {
>>       union sidtab_entry_inner *entry;
>>       u32 level, capacity_shift, leaf_index = index / 
>> SIDTAB_LEAF_ENTRIES;
>> @@ -125,10 +145,16 @@ static struct context *sidtab_do_lookup(struct 
>> sidtab *s, u32 index, int alloc)
>>           if (!entry->ptr_leaf)
>>               return NULL;
>>       }
>> -    return &entry->ptr_leaf->entries[index % 
>> SIDTAB_LEAF_ENTRIES].context;
>> +    return &entry->ptr_leaf->entries[index % SIDTAB_LEAF_ENTRIES];
>> +}
>> +
>> +/* use when you know that there is enough entries */
>> +static struct context *sidtab_lookup_unsafe(struct sidtab *s, u32 index)
>> +{
>> +    return &sidtab_do_lookup(s, index, 0)->context;
>>   }
>> -static struct context *sidtab_lookup(struct sidtab *s, u32 index)
>> +static struct sidtab_entry *sidtab_lookup(struct sidtab *s, u32 index)
>>   {
>>       /* read entries only after reading count */
>>       u32 count = smp_load_acquire(&s->count);
>> @@ -139,33 +165,34 @@ static struct context *sidtab_lookup(struct 
>> sidtab *s, u32 index)
>>       return sidtab_do_lookup(s, index, 0);
>>   }
>> -static struct context *sidtab_lookup_initial(struct sidtab *s, u32 sid)
>> +static struct sidtab_entry *sidtab_lookup_initial(struct sidtab *s, 
>> u32 sid)
>>   {
>> -    return s->isids[sid - 1].set ? &s->isids[sid - 1].context : NULL;
>> +    return s->isids[sid - 1].set ? &s->isids[sid - 1].entry : NULL;
>>   }
>> -static struct context *sidtab_search_core(struct sidtab *s, u32 sid, 
>> int force)
>> +static struct sidtab_entry *sidtab_search_core(struct sidtab *s, u32 
>> sid,
>> +                           int force)
>>   {
>> -    struct context *context;
>> -
>>       if (sid != 0) {
>> +        struct sidtab_entry *entry;
>> +
>>           if (sid > SECINITSID_NUM)
>> -            context = sidtab_lookup(s, sid - (SECINITSID_NUM + 1));
>> +            entry = sidtab_lookup(s, sid - (SECINITSID_NUM + 1));
>>           else
>> -            context = sidtab_lookup_initial(s, sid);
>> -        if (context && (!context->len || force))
>> -            return context;
>> +            entry = sidtab_lookup_initial(s, sid);
>> +        if (entry && (!entry->context.len || force))
>> +            return entry;
>>       }
>>       return sidtab_lookup_initial(s, SECINITSID_UNLABELED);
>>   }
>> -struct context *sidtab_search(struct sidtab *s, u32 sid)
>> +struct sidtab_entry *sidtab_search_entry(struct sidtab *s, u32 sid)
>>   {
>>       return sidtab_search_core(s, sid, 0);
>>   }
>> -struct context *sidtab_search_force(struct sidtab *s, u32 sid)
>> +struct sidtab_entry *sidtab_search_entry_force(struct sidtab *s, u32 
>> sid)
>>   {
>>       return sidtab_search_core(s, sid, 1);
>>   }
>> @@ -230,7 +257,7 @@ static int sidtab_rcache_search(struct sidtab *s, 
>> struct context *context,
>>           if (v >= SIDTAB_MAX)
>>               continue;
>> -        if (context_cmp(sidtab_do_lookup(s, v, 0), context)) {
>> +        if (context_cmp(sidtab_lookup_unsafe(s, v), context)) {
>>               sidtab_rcache_update(s, v, i);
>>               *index = v;
>>               return 0;
>> @@ -245,7 +272,7 @@ static int sidtab_reverse_lookup(struct sidtab *s, 
>> struct context *context,
>>       unsigned long flags;
>>       u32 count, count_locked, level, pos;
>>       struct sidtab_convert_params *convert;
>> -    struct context *dst, *dst_convert;
>> +    struct sidtab_entry *dst, *dst_convert;
>>       int rc;
>>       rc = sidtab_rcache_search(s, context, index);
>> @@ -273,7 +300,7 @@ static int sidtab_reverse_lookup(struct sidtab *s, 
>> struct context *context,
>>       /* if count has changed before we acquired the lock, then catch 
>> up */
>>       while (count < count_locked) {
>> -        if (context_cmp(sidtab_do_lookup(s, count, 0), context)) {
>> +        if (context_cmp(sidtab_lookup_unsafe(s, count), context)) {
>>               sidtab_rcache_push(s, count);
>>               *index = count;
>>               rc = 0;
>> @@ -293,7 +320,7 @@ static int sidtab_reverse_lookup(struct sidtab *s, 
>> struct context *context,
>>       if (!dst)
>>           goto out_unlock;
>> -    rc = context_cpy(dst, context);
>> +    rc = context_cpy(&dst->context, context);
>>       if (rc)
>>           goto out_unlock;
>> @@ -305,13 +332,14 @@ static int sidtab_reverse_lookup(struct sidtab 
>> *s, struct context *context,
>>           rc = -ENOMEM;
>>           dst_convert = sidtab_do_lookup(convert->target, count, 1);
>>           if (!dst_convert) {
>> -            context_destroy(dst);
>> +            context_destroy(&dst->context);
>>               goto out_unlock;
>>           }
>> -        rc = convert->func(context, dst_convert, convert->args);
>> +        rc = convert->func(context, &dst_convert->context,
>> +                   convert->args);
>>           if (rc) {
>> -            context_destroy(dst);
>> +            context_destroy(&dst->context);
>>               goto out_unlock;
>>           }
>> @@ -341,9 +369,9 @@ int sidtab_context_to_sid(struct sidtab *s, struct 
>> context *context, u32 *sid)
>>       u32 i;
>>       for (i = 0; i < SECINITSID_NUM; i++) {
>> -        struct sidtab_isid_entry *entry = &s->isids[i];
>> +        struct sidtab_isid_entry *isid = &s->isids[i];
>> -        if (entry->set && context_cmp(context, &entry->context)) {
>> +        if (isid->set && context_cmp(context, &isid->entry.context)) {
>>               *sid = i + 1;
>>               return 0;
>>           }
>> @@ -453,6 +481,14 @@ int sidtab_convert(struct sidtab *s, struct 
>> sidtab_convert_params *params)
>>       return rc;
>>   }
>> +static void sidtab_destroy_entry(struct sidtab_entry *entry)
>> +{
>> +    context_destroy(&entry->context);
>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>> +    kfree(entry->cache);
>> +#endif
>> +}
>> +
>>   static void sidtab_destroy_tree(union sidtab_entry_inner entry, u32 
>> level)
>>   {
>>       u32 i;
>> @@ -473,7 +509,7 @@ static void sidtab_destroy_tree(union 
>> sidtab_entry_inner entry, u32 level)
>>               return;
>>           for (i = 0; i < SIDTAB_LEAF_ENTRIES; i++)
>> -            context_destroy(&node->entries[i].context);
>> +            sidtab_destroy_entry(&node->entries[i]);
>>           kfree(node);
>>       }
>>   }
>> @@ -484,7 +520,7 @@ void sidtab_destroy(struct sidtab *s)
>>       for (i = 0; i < SECINITSID_NUM; i++)
>>           if (s->isids[i].set)
>> -            context_destroy(&s->isids[i].context);
>> +            sidtab_destroy_entry(&s->isids[i].entry);
>>       level = SIDTAB_MAX_LEVEL;
>>       while (level && !s->roots[level].ptr_inner)
>> @@ -492,3 +528,87 @@ void sidtab_destroy(struct sidtab *s)
>>       sidtab_destroy_tree(s->roots[level], level);
>>   }
>> +
>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>> +
>> +void sidtab_sid2str_put(struct sidtab *s, struct sidtab_entry *entry,
>> +            const char *str, u32 str_len)
>> +{
>> +    struct sidtab_str_cache *cache, *victim;
>> +
>> +    /* do not cache invalid contexts */
>> +    if (entry->context.len)
>> +        return;
>> +
>> +    /*
>> +     * Skip the put operation when in non-task context to avoid the need
>> +     * to disable interrupts while holding s->cache_lock.
>> +     */
>> +    if (!in_task())
>> +        return;
>> +
>> +    spin_lock(&s->cache_lock);
>> +
>> +    if (entry->cache) {
>> +        /* entry in cache - just bump to he head of LRU list */
>> +        list_move(&entry->cache->lru_member, &s->cache_lru_list);
>> +        goto out_unlock;
>> +    }
>> +
>> +    cache = kmalloc(sizeof(struct sidtab_str_cache) + str_len, 
>> GFP_ATOMIC);
>> +    if (!cache)
>> +        goto out_unlock;
>> +
>> +    if (s->cache_free_slots == 0) {
>> +        /* pop a cache entry from the tail and free it */
>> +        victim = container_of(s->cache_lru_list.prev,
>> +                      struct sidtab_str_cache, lru_member);
>> +        list_del(&victim->lru_member);
>> +        kfree_rcu(victim, rcu_member);
>> +        rcu_assign_pointer(victim->parent->cache, NULL);
>> +    } else {
>> +        s->cache_free_slots--;
>> +    }
>> +    cache->parent = entry;
>> +    cache->len = str_len;
>> +    memcpy(cache->str, str, str_len);
>> +    rcu_head_init(&cache->rcu_member);
>> +    list_add(&cache->lru_member, &s->cache_lru_list);
>> +
>> +    rcu_assign_pointer(entry->cache, cache);
>> +
>> +out_unlock:
>> +    spin_unlock(&s->cache_lock);
>> +}
>> +
>> +int sidtab_sid2str_get(struct sidtab *s, struct sidtab_entry *entry,
>> +               char **out, u32 *out_len)
>> +{
>> +    struct sidtab_str_cache *cache;
>> +    int rc = 0;
>> +
>> +    if (entry->context.len)
>> +        return -ENOENT; /* do not cache invalid contexts */
>> +
>> +    rcu_read_lock();
>> +
>> +    cache = rcu_dereference(entry->cache);
>> +    if (!cache) {
>> +        rc = -ENOENT;
>> +    } else {
>> +        *out_len = cache->len;
>> +        if (out) {
>> +            *out = kmemdup(cache->str, cache->len, GFP_ATOMIC);
>> +            if (!*out)
>> +                rc = -ENOMEM;
>> +        }
>> +    }
>> +
>> +    rcu_read_unlock();
>> +
>> +    if (!rc && out)
>> +        sidtab_sid2str_put(s, entry, *out, *out_len);
>> +    return rc;
>> +}
>> +
>> +#endif /* CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0 */
>> diff --git a/security/selinux/ss/sidtab.h b/security/selinux/ss/sidtab.h
>> index 1f4763141aa1..9159a300bde3 100644
>> --- a/security/selinux/ss/sidtab.h
>> +++ b/security/selinux/ss/sidtab.h
>> @@ -16,13 +16,13 @@
>>   #include "context.h"
>> -struct sidtab_entry_leaf {
>> +struct sidtab_entry {
>>       struct context context;
>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>> +    struct sidtab_str_cache *cache;
>> +#endif
>>   };
>> -struct sidtab_node_inner;
>> -struct sidtab_node_leaf;
>> -
>>   union sidtab_entry_inner {
>>       struct sidtab_node_inner *ptr_inner;
>>       struct sidtab_node_leaf  *ptr_leaf;
>> @@ -38,7 +38,7 @@ union sidtab_entry_inner {
>>       (SIDTAB_NODE_ALLOC_SHIFT - size_to_shift(sizeof(union 
>> sidtab_entry_inner)))
>>   #define SIDTAB_INNER_ENTRIES ((size_t)1 << SIDTAB_INNER_SHIFT)
>>   #define SIDTAB_LEAF_ENTRIES \
>> -    (SIDTAB_NODE_ALLOC_SIZE / sizeof(struct sidtab_entry_leaf))
>> +    (SIDTAB_NODE_ALLOC_SIZE / sizeof(struct sidtab_entry))
>>   #define SIDTAB_MAX_BITS 32
>>   #define SIDTAB_MAX U32_MAX
>> @@ -48,7 +48,7 @@ union sidtab_entry_inner {
>>                SIDTAB_INNER_SHIFT)
>>   struct sidtab_node_leaf {
>> -    struct sidtab_entry_leaf entries[SIDTAB_LEAF_ENTRIES];
>> +    struct sidtab_entry entries[SIDTAB_LEAF_ENTRIES];
>>   };
>>   struct sidtab_node_inner {
>> @@ -57,7 +57,7 @@ struct sidtab_node_inner {
>>   struct sidtab_isid_entry {
>>       int set;
>> -    struct context context;
>> +    struct sidtab_entry entry;
>>   };
>>   struct sidtab_convert_params {
>> @@ -83,6 +83,13 @@ struct sidtab {
>>       struct sidtab_convert_params *convert;
>>       spinlock_t lock;
>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>> +    /* SID -> context string cache */
>> +    u32 cache_free_slots;
>> +    struct list_head cache_lru_list;
>> +    spinlock_t cache_lock;
>> +#endif
>> +
>>       /* reverse lookup cache - access atomically via 
>> {READ|WRITE}_ONCE() */
>>       u32 rcache[SIDTAB_RCACHE_SIZE];
>> @@ -92,8 +99,22 @@ struct sidtab {
>>   int sidtab_init(struct sidtab *s);
>>   int sidtab_set_initial(struct sidtab *s, u32 sid, struct context 
>> *context);
>> -struct context *sidtab_search(struct sidtab *s, u32 sid);
>> -struct context *sidtab_search_force(struct sidtab *s, u32 sid);
>> +struct sidtab_entry *sidtab_search_entry(struct sidtab *s, u32 sid);
>> +struct sidtab_entry *sidtab_search_entry_force(struct sidtab *s, u32 
>> sid);
>> +
>> +static inline struct context *sidtab_search(struct sidtab *s, u32 sid)
>> +{
>> +    struct sidtab_entry *entry = sidtab_search_entry(s, sid);
>> +
>> +    return entry ? &entry->context : NULL;
>> +}
>> +
>> +static inline struct context *sidtab_search_force(struct sidtab *s, 
>> u32 sid)
>> +{
>> +    struct sidtab_entry *entry = sidtab_search_entry_force(s, sid);
>> +
>> +    return entry ? &entry->context : NULL;
>> +}
>>   int sidtab_convert(struct sidtab *s, struct sidtab_convert_params 
>> *params);
>> @@ -101,6 +122,25 @@ int sidtab_context_to_sid(struct sidtab *s, 
>> struct context *context, u32 *sid);
>>   void sidtab_destroy(struct sidtab *s);
>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>> +void sidtab_sid2str_put(struct sidtab *s, struct sidtab_entry *entry,
>> +            const char *str, u32 str_len);
>> +int sidtab_sid2str_get(struct sidtab *s, struct sidtab_entry *entry,
>> +               char **out, u32 *out_len);
>> +#else
>> +static inline void sidtab_sid2str_put(struct sidtab *s,
>> +                      struct sidtab_entry *entry,
>> +                      const char *str, u32 str_len)
>> +{
>> +}
>> +static inline int sidtab_sid2str_get(struct sidtab *s,
>> +                     struct sidtab_entry *entry,
>> +                     char **out, u32 *out_len)
>> +{
>> +    return -ENOENT;
>> +}
>> +#endif /* CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0 */
>> +
>>   #endif    /* _SS_SIDTAB_H_ */
>>
>

Stephen Smalley Nov. 6, 2019, 7:47 p.m. UTC | #3

On 11/6/19 2:22 PM, Stephen Smalley wrote:
> On 11/6/19 11:11 AM, Stephen Smalley wrote:
>> On 11/6/19 3:26 AM, Ondrej Mosnacek wrote:
>>> Translating a context struct to string can be quite slow, especially if
>>> the context has a lot of category bits set. This can cause quite
>>> noticeable performance impact in situations where the translation needs
>>> to be done repeatedly. A common example is a UNIX datagram socket with
>>> the SO_PASSSEC option enabled, which is used e.g. by systemd-journald
>>> when receiving log messages via datagram socket. This scenario can be
>>> reproduced with:
>>>
>>>      cat /dev/urandom | base64 | logger &
>>>      timeout 30s perf record -p $(pidof systemd-journald) -a -g
>>>      kill %1
>>>      perf report -g none --pretty raw | grep security_secid_to_secctx
>>>
>>> Before the caching introduced by this patch, computing the context
>>> string (security_secid_to_secctx() function) takes up ~65% of
>>> systemd-journald's CPU time (assuming a context with 1024 categories
>>> set and Fedora x86_64 release kernel configs). After this patch
>>> (assuming near-perfect cache hit ratio) this overhead is reduced to just
>>> ~2%.
>>>
>>> This patch addresses the issue by caching a certain number (compile-time
>>> configurable) of recently used context strings to speed up repeated
>>> translations of the same context, while using only a small amount of
>>> memory.
>>>
>>> The cache is integrated into the existing sidtab table by adding a field
>>> to each entry, which when not NULL contains an RCU-protected pointer to
>>> a cache entry containing the cached string. The cache entries are kept
>>> in a linked list sorted according to how recently they were used. On a
>>> cache miss when the cache is full, the least recently used entry is
>>> removed to make space for the new entry.
>>>
>>> The patch migrates security_sid_to_context_core() to use the cache (also
>>> a few other functions where it was possible without too much fuss, but
>>> these mostly use the translation for logging in case of error, which is
>>> rare).
>>>
>>> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1733259
>>> Cc: Michal Sekletar <msekleta@redhat.com>
>>> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
>>
>> This looks good to me and didn't trigger any issues during testing. 
>> Might want to run it by the RCU wizards, e.g. Paul McKenney, to 
>> confirm that it is correct and optimal usage of RCU.  I didn't see 
>> anywhere near the same degree of performance improvement in running 
>> your reproducer above but I also have all the kernel debugging options 
>> enabled so perhaps those are creating noise or perhaps the reproducer 
>> doesn't yield stable results.
> 
> Rebuilding with the stock Fedora x86_64 kernel config was closer to your 
> results albeit still different, ~35% before and ~2% after.

Ah, I can reproduce your ~65% result on the 5.3-based Fedora kernel, but 
not with mainline 5.4.0-rc1.  Only SELinux change between those two that 
seems potentially relevant is your "selinux: avoid atomic_t usage in 
sidtab" patch.

> 
>>   Regardless, you can add:
>>
>> Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
>> Tested-by: Stephen Smalley <sds@tycho.nsa.gov>
>>
>>> ---
>>>   security/selinux/Kconfig       |  11 ++
>>>   security/selinux/ss/services.c | 138 +++++++++++++++----------
>>>   security/selinux/ss/sidtab.c   | 178 +++++++++++++++++++++++++++------
>>>   security/selinux/ss/sidtab.h   |  58 +++++++++--
>>>   4 files changed, 293 insertions(+), 92 deletions(-)
>>>
>>> Changes in v2:
>>>   - skip sidtab_sid2str_put() when in non-task context to prevent
>>>     deadlock while avoiding the need to lock the spinlock with
>>>     irqsave/-restore (which is slower)
>>>
>>> diff --git a/security/selinux/Kconfig b/security/selinux/Kconfig
>>> index 5711689deb6a..35fe8878cf1c 100644
>>> --- a/security/selinux/Kconfig
>>> +++ b/security/selinux/Kconfig
>>> @@ -85,3 +85,14 @@ config SECURITY_SELINUX_CHECKREQPROT_VALUE
>>>         via /selinux/checkreqprot if authorized by policy.
>>>         If you are unsure how to answer this question, answer 0.
>>> +
>>> +config SECURITY_SELINUX_SID2STR_CACHE_SIZE
>>> +    int "NSA SELinux SID to context string translation cache size"
>>> +    depends on SECURITY_SELINUX
>>> +    default 256
>>> +    help
>>> +      This option defines the size of the internal SID -> context 
>>> string
>>> +      cache, which improves the performance of context to string
>>> +      conversion.  Setting this option to 0 disables the cache 
>>> completely.
>>> +
>>> +      If unsure, keep the default value.
>>> diff --git a/security/selinux/ss/services.c 
>>> b/security/selinux/ss/services.c
>>> index 3a29e7c24ba9..b6dda5261166 100644
>>> --- a/security/selinux/ss/services.c
>>> +++ b/security/selinux/ss/services.c
>>> @@ -91,6 +91,12 @@ static int context_struct_to_string(struct 
>>> policydb *policydb,
>>>                       char **scontext,
>>>                       u32 *scontext_len);
>>> +static int sidtab_entry_to_string(struct policydb *policydb,
>>> +                  struct sidtab *sidtab,
>>> +                  struct sidtab_entry *entry,
>>> +                  char **scontext,
>>> +                  u32 *scontext_len);
>>> +
>>>   static void context_struct_compute_av(struct policydb *policydb,
>>>                         struct context *scontext,
>>>                         struct context *tcontext,
>>> @@ -716,20 +722,21 @@ static void context_struct_compute_av(struct 
>>> policydb *policydb,
>>>   }
>>>   static int security_validtrans_handle_fail(struct selinux_state 
>>> *state,
>>> -                       struct context *ocontext,
>>> -                       struct context *ncontext,
>>> -                       struct context *tcontext,
>>> +                       struct sidtab_entry *oentry,
>>> +                       struct sidtab_entry *nentry,
>>> +                       struct sidtab_entry *tentry,
>>>                          u16 tclass)
>>>   {
>>>       struct policydb *p = &state->ss->policydb;
>>> +    struct sidtab *sidtab = state->ss->sidtab;
>>>       char *o = NULL, *n = NULL, *t = NULL;
>>>       u32 olen, nlen, tlen;
>>> -    if (context_struct_to_string(p, ocontext, &o, &olen))
>>> +    if (sidtab_entry_to_string(p, sidtab, oentry, &o, &olen))
>>>           goto out;
>>> -    if (context_struct_to_string(p, ncontext, &n, &nlen))
>>> +    if (sidtab_entry_to_string(p, sidtab, nentry, &n, &nlen))
>>>           goto out;
>>> -    if (context_struct_to_string(p, tcontext, &t, &tlen))
>>> +    if (sidtab_entry_to_string(p, sidtab, tentry, &t, &tlen))
>>>           goto out;
>>>       audit_log(audit_context(), GFP_ATOMIC, AUDIT_SELINUX_ERR,
>>>             "op=security_validate_transition seresult=denied"
>>> @@ -751,9 +758,9 @@ static int security_compute_validatetrans(struct 
>>> selinux_state *state,
>>>   {
>>>       struct policydb *policydb;
>>>       struct sidtab *sidtab;
>>> -    struct context *ocontext;
>>> -    struct context *ncontext;
>>> -    struct context *tcontext;
>>> +    struct sidtab_entry *oentry;
>>> +    struct sidtab_entry *nentry;
>>> +    struct sidtab_entry *tentry;
>>>       struct class_datum *tclass_datum;
>>>       struct constraint_node *constraint;
>>>       u16 tclass;
>>> @@ -779,24 +786,24 @@ static int 
>>> security_compute_validatetrans(struct selinux_state *state,
>>>       }
>>>       tclass_datum = policydb->class_val_to_struct[tclass - 1];
>>> -    ocontext = sidtab_search(sidtab, oldsid);
>>> -    if (!ocontext) {
>>> +    oentry = sidtab_search_entry(sidtab, oldsid);
>>> +    if (!oentry) {
>>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>>               __func__, oldsid);
>>>           rc = -EINVAL;
>>>           goto out;
>>>       }
>>> -    ncontext = sidtab_search(sidtab, newsid);
>>> -    if (!ncontext) {
>>> +    nentry = sidtab_search_entry(sidtab, newsid);
>>> +    if (!nentry) {
>>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>>               __func__, newsid);
>>>           rc = -EINVAL;
>>>           goto out;
>>>       }
>>> -    tcontext = sidtab_search(sidtab, tasksid);
>>> -    if (!tcontext) {
>>> +    tentry = sidtab_search_entry(sidtab, tasksid);
>>> +    if (!tentry) {
>>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>>               __func__, tasksid);
>>>           rc = -EINVAL;
>>> @@ -805,15 +812,16 @@ static int 
>>> security_compute_validatetrans(struct selinux_state *state,
>>>       constraint = tclass_datum->validatetrans;
>>>       while (constraint) {
>>> -        if (!constraint_expr_eval(policydb, ocontext, ncontext,
>>> -                      tcontext, constraint->expr)) {
>>> +        if (!constraint_expr_eval(policydb, &oentry->context,
>>> +                      &nentry->context, &tentry->context,
>>> +                      constraint->expr)) {
>>>               if (user)
>>>                   rc = -EPERM;
>>>               else
>>>                   rc = security_validtrans_handle_fail(state,
>>> -                                     ocontext,
>>> -                                     ncontext,
>>> -                                     tcontext,
>>> +                                     oentry,
>>> +                                     nentry,
>>> +                                     tentry,
>>>                                        tclass);
>>>               goto out;
>>>           }
>>> @@ -855,7 +863,7 @@ int security_bounded_transition(struct 
>>> selinux_state *state,
>>>   {
>>>       struct policydb *policydb;
>>>       struct sidtab *sidtab;
>>> -    struct context *old_context, *new_context;
>>> +    struct sidtab_entry *old_entry, *new_entry;
>>>       struct type_datum *type;
>>>       int index;
>>>       int rc;
>>> @@ -869,16 +877,16 @@ int security_bounded_transition(struct 
>>> selinux_state *state,
>>>       sidtab = state->ss->sidtab;
>>>       rc = -EINVAL;
>>> -    old_context = sidtab_search(sidtab, old_sid);
>>> -    if (!old_context) {
>>> +    old_entry = sidtab_search_entry(sidtab, old_sid);
>>> +    if (!old_entry) {
>>>           pr_err("SELinux: %s: unrecognized SID %u\n",
>>>                  __func__, old_sid);
>>>           goto out;
>>>       }
>>>       rc = -EINVAL;
>>> -    new_context = sidtab_search(sidtab, new_sid);
>>> -    if (!new_context) {
>>> +    new_entry = sidtab_search_entry(sidtab, new_sid);
>>> +    if (!new_entry) {
>>>           pr_err("SELinux: %s: unrecognized SID %u\n",
>>>                  __func__, new_sid);
>>>           goto out;
>>> @@ -886,10 +894,10 @@ int security_bounded_transition(struct 
>>> selinux_state *state,
>>>       rc = 0;
>>>       /* type/domain unchanged */
>>> -    if (old_context->type == new_context->type)
>>> +    if (old_entry->context.type == new_entry->context.type)
>>>           goto out;
>>> -    index = new_context->type;
>>> +    index = new_entry->context.type;
>>>       while (true) {
>>>           type = policydb->type_val_to_struct[index - 1];
>>>           BUG_ON(!type);
>>> @@ -901,7 +909,7 @@ int security_bounded_transition(struct 
>>> selinux_state *state,
>>>           /* @newsid is bounded by @oldsid */
>>>           rc = 0;
>>> -        if (type->bounds == old_context->type)
>>> +        if (type->bounds == old_entry->context.type)
>>>               break;
>>>           index = type->bounds;
>>> @@ -912,10 +920,10 @@ int security_bounded_transition(struct 
>>> selinux_state *state,
>>>           char *new_name = NULL;
>>>           u32 length;
>>> -        if (!context_struct_to_string(policydb, old_context,
>>> -                          &old_name, &length) &&
>>> -            !context_struct_to_string(policydb, new_context,
>>> -                          &new_name, &length)) {
>>> +        if (!sidtab_entry_to_string(policydb, sidtab, old_entry,
>>> +                        &old_name, &length) &&
>>> +            !sidtab_entry_to_string(policydb, sidtab, new_entry,
>>> +                        &new_name, &length)) {
>>>               audit_log(audit_context(),
>>>                     GFP_ATOMIC, AUDIT_SELINUX_ERR,
>>>                     "op=security_bounded_transition "
>>> @@ -1255,6 +1263,23 @@ static int context_struct_to_string(struct 
>>> policydb *p,
>>>       return 0;
>>>   }
>>> +static int sidtab_entry_to_string(struct policydb *p,
>>> +                  struct sidtab *sidtab,
>>> +                  struct sidtab_entry *entry,
>>> +                  char **scontext, u32 *scontext_len)
>>> +{
>>> +    int rc = sidtab_sid2str_get(sidtab, entry, scontext, scontext_len);
>>> +
>>> +    if (rc != -ENOENT)
>>> +        return rc;
>>> +
>>> +    rc = context_struct_to_string(p, &entry->context, scontext,
>>> +                      scontext_len);
>>> +    if (!rc && scontext)
>>> +        sidtab_sid2str_put(sidtab, entry, *scontext, *scontext_len);
>>> +    return rc;
>>> +}
>>> +
>>>   #include "initial_sid_to_string.h"
>>>   const char *security_get_initial_sid_context(u32 sid)
>>> @@ -1271,7 +1296,7 @@ static int security_sid_to_context_core(struct 
>>> selinux_state *state,
>>>   {
>>>       struct policydb *policydb;
>>>       struct sidtab *sidtab;
>>> -    struct context *context;
>>> +    struct sidtab_entry *entry;
>>>       int rc = 0;
>>>       if (scontext)
>>> @@ -1302,21 +1327,23 @@ static int 
>>> security_sid_to_context_core(struct selinux_state *state,
>>>       read_lock(&state->ss->policy_rwlock);
>>>       policydb = &state->ss->policydb;
>>>       sidtab = state->ss->sidtab;
>>> +
>>>       if (force)
>>> -        context = sidtab_search_force(sidtab, sid);
>>> +        entry = sidtab_search_entry_force(sidtab, sid);
>>>       else
>>> -        context = sidtab_search(sidtab, sid);
>>> -    if (!context) {
>>> +        entry = sidtab_search_entry(sidtab, sid);
>>> +    if (!entry) {
>>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>>               __func__, sid);
>>>           rc = -EINVAL;
>>>           goto out_unlock;
>>>       }
>>> -    if (only_invalid && !context->len)
>>> -        rc = 0;
>>> -    else
>>> -        rc = context_struct_to_string(policydb, context, scontext,
>>> -                          scontext_len);
>>> +    if (only_invalid && !entry->context.len)
>>> +        goto out_unlock;
>>> +
>>> +    rc = sidtab_entry_to_string(policydb, sidtab, entry, scontext,
>>> +                    scontext_len);
>>> +
>>>   out_unlock:
>>>       read_unlock(&state->ss->policy_rwlock);
>>>   out:
>>> @@ -1574,19 +1601,20 @@ int security_context_to_sid_force(struct 
>>> selinux_state *state,
>>>   static int compute_sid_handle_invalid_context(
>>>       struct selinux_state *state,
>>> -    struct context *scontext,
>>> -    struct context *tcontext,
>>> +    struct sidtab_entry *sentry,
>>> +    struct sidtab_entry *tentry,
>>>       u16 tclass,
>>>       struct context *newcontext)
>>>   {
>>>       struct policydb *policydb = &state->ss->policydb;
>>> +    struct sidtab *sidtab = state->ss->sidtab;
>>>       char *s = NULL, *t = NULL, *n = NULL;
>>>       u32 slen, tlen, nlen;
>>>       struct audit_buffer *ab;
>>> -    if (context_struct_to_string(policydb, scontext, &s, &slen))
>>> +    if (sidtab_entry_to_string(policydb, sidtab, sentry, &s, &slen))
>>>           goto out;
>>> -    if (context_struct_to_string(policydb, tcontext, &t, &tlen))
>>> +    if (sidtab_entry_to_string(policydb, sidtab, tentry, &t, &tlen))
>>>           goto out;
>>>       if (context_struct_to_string(policydb, newcontext, &n, &nlen))
>>>           goto out;
>>> @@ -1645,7 +1673,8 @@ static int security_compute_sid(struct 
>>> selinux_state *state,
>>>       struct policydb *policydb;
>>>       struct sidtab *sidtab;
>>>       struct class_datum *cladatum = NULL;
>>> -    struct context *scontext = NULL, *tcontext = NULL, newcontext;
>>> +    struct context *scontext, *tcontext, newcontext;
>>> +    struct sidtab_entry *sentry, *tentry;
>>>       struct role_trans *roletr = NULL;
>>>       struct avtab_key avkey;
>>>       struct avtab_datum *avdatum;
>>> @@ -1682,21 +1711,24 @@ static int security_compute_sid(struct 
>>> selinux_state *state,
>>>       policydb = &state->ss->policydb;
>>>       sidtab = state->ss->sidtab;
>>> -    scontext = sidtab_search(sidtab, ssid);
>>> -    if (!scontext) {
>>> +    sentry = sidtab_search_entry(sidtab, ssid);
>>> +    if (!sentry) {
>>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>>                  __func__, ssid);
>>>           rc = -EINVAL;
>>>           goto out_unlock;
>>>       }
>>> -    tcontext = sidtab_search(sidtab, tsid);
>>> -    if (!tcontext) {
>>> +    tentry = sidtab_search_entry(sidtab, tsid);
>>> +    if (!tentry) {
>>>           pr_err("SELinux: %s:  unrecognized SID %d\n",
>>>                  __func__, tsid);
>>>           rc = -EINVAL;
>>>           goto out_unlock;
>>>       }
>>> +    scontext = &sentry->context;
>>> +    tcontext = &tentry->context;
>>> +
>>>       if (tclass && tclass <= policydb->p_classes.nprim)
>>>           cladatum = policydb->class_val_to_struct[tclass - 1];
>>> @@ -1797,10 +1829,8 @@ static int security_compute_sid(struct 
>>> selinux_state *state,
>>>       /* Check the validity of the context. */
>>>       if (!policydb_context_isvalid(policydb, &newcontext)) {
>>> -        rc = compute_sid_handle_invalid_context(state, scontext,
>>> -                            tcontext,
>>> -                            tclass,
>>> -                            &newcontext);
>>> +        rc = compute_sid_handle_invalid_context(state, sentry, tentry,
>>> +                            tclass, &newcontext);
>>>           if (rc)
>>>               goto out_unlock;
>>>       }
>>> diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
>>> index 7d49994e8d5f..6210d7ff3e31 100644
>>> --- a/security/selinux/ss/sidtab.c
>>> +++ b/security/selinux/ss/sidtab.c
>>> @@ -9,6 +9,8 @@
>>>    */
>>>   #include <linux/errno.h>
>>>   #include <linux/kernel.h>
>>> +#include <linux/list.h>
>>> +#include <linux/rcupdate.h>
>>>   #include <linux/slab.h>
>>>   #include <linux/sched.h>
>>>   #include <linux/spinlock.h>
>>> @@ -17,6 +19,14 @@
>>>   #include "security.h"
>>>   #include "sidtab.h"
>>> +struct sidtab_str_cache {
>>> +    struct rcu_head rcu_member;
>>> +    struct list_head lru_member;
>>> +    struct sidtab_entry *parent;
>>> +    u32 len;
>>> +    char str[];
>>> +};
>>> +
>>>   int sidtab_init(struct sidtab *s)
>>>   {
>>>       u32 i;
>>> @@ -34,24 +44,33 @@ int sidtab_init(struct sidtab *s)
>>>       s->convert = NULL;
>>>       spin_lock_init(&s->lock);
>>> +
>>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>>> +    s->cache_free_slots = CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE;
>>> +    INIT_LIST_HEAD(&s->cache_lru_list);
>>> +    spin_lock_init(&s->cache_lock);
>>> +#endif
>>>       return 0;
>>>   }
>>>   int sidtab_set_initial(struct sidtab *s, u32 sid, struct context 
>>> *context)
>>>   {
>>> -    struct sidtab_isid_entry *entry;
>>> +    struct sidtab_isid_entry *isid;
>>>       int rc;
>>>       if (sid == 0 || sid > SECINITSID_NUM)
>>>           return -EINVAL;
>>> -    entry = &s->isids[sid - 1];
>>> +    isid = &s->isids[sid - 1];
>>> -    rc = context_cpy(&entry->context, context);
>>> +    rc = context_cpy(&isid->entry.context, context);
>>>       if (rc)
>>>           return rc;
>>> -    entry->set = 1;
>>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>>> +    isid->entry.cache = NULL;
>>> +#endif
>>> +    isid->set = 1;
>>>       return 0;
>>>   }
>>> @@ -88,7 +107,8 @@ static int sidtab_alloc_roots(struct sidtab *s, 
>>> u32 level)
>>>       return 0;
>>>   }
>>> -static struct context *sidtab_do_lookup(struct sidtab *s, u32 index, 
>>> int alloc)
>>> +static struct sidtab_entry *sidtab_do_lookup(struct sidtab *s, u32 
>>> index,
>>> +                         int alloc)
>>>   {
>>>       union sidtab_entry_inner *entry;
>>>       u32 level, capacity_shift, leaf_index = index / 
>>> SIDTAB_LEAF_ENTRIES;
>>> @@ -125,10 +145,16 @@ static struct context *sidtab_do_lookup(struct 
>>> sidtab *s, u32 index, int alloc)
>>>           if (!entry->ptr_leaf)
>>>               return NULL;
>>>       }
>>> -    return &entry->ptr_leaf->entries[index % 
>>> SIDTAB_LEAF_ENTRIES].context;
>>> +    return &entry->ptr_leaf->entries[index % SIDTAB_LEAF_ENTRIES];
>>> +}
>>> +
>>> +/* use when you know that there is enough entries */
>>> +static struct context *sidtab_lookup_unsafe(struct sidtab *s, u32 
>>> index)
>>> +{
>>> +    return &sidtab_do_lookup(s, index, 0)->context;
>>>   }
>>> -static struct context *sidtab_lookup(struct sidtab *s, u32 index)
>>> +static struct sidtab_entry *sidtab_lookup(struct sidtab *s, u32 index)
>>>   {
>>>       /* read entries only after reading count */
>>>       u32 count = smp_load_acquire(&s->count);
>>> @@ -139,33 +165,34 @@ static struct context *sidtab_lookup(struct 
>>> sidtab *s, u32 index)
>>>       return sidtab_do_lookup(s, index, 0);
>>>   }
>>> -static struct context *sidtab_lookup_initial(struct sidtab *s, u32 sid)
>>> +static struct sidtab_entry *sidtab_lookup_initial(struct sidtab *s, 
>>> u32 sid)
>>>   {
>>> -    return s->isids[sid - 1].set ? &s->isids[sid - 1].context : NULL;
>>> +    return s->isids[sid - 1].set ? &s->isids[sid - 1].entry : NULL;
>>>   }
>>> -static struct context *sidtab_search_core(struct sidtab *s, u32 sid, 
>>> int force)
>>> +static struct sidtab_entry *sidtab_search_core(struct sidtab *s, u32 
>>> sid,
>>> +                           int force)
>>>   {
>>> -    struct context *context;
>>> -
>>>       if (sid != 0) {
>>> +        struct sidtab_entry *entry;
>>> +
>>>           if (sid > SECINITSID_NUM)
>>> -            context = sidtab_lookup(s, sid - (SECINITSID_NUM + 1));
>>> +            entry = sidtab_lookup(s, sid - (SECINITSID_NUM + 1));
>>>           else
>>> -            context = sidtab_lookup_initial(s, sid);
>>> -        if (context && (!context->len || force))
>>> -            return context;
>>> +            entry = sidtab_lookup_initial(s, sid);
>>> +        if (entry && (!entry->context.len || force))
>>> +            return entry;
>>>       }
>>>       return sidtab_lookup_initial(s, SECINITSID_UNLABELED);
>>>   }
>>> -struct context *sidtab_search(struct sidtab *s, u32 sid)
>>> +struct sidtab_entry *sidtab_search_entry(struct sidtab *s, u32 sid)
>>>   {
>>>       return sidtab_search_core(s, sid, 0);
>>>   }
>>> -struct context *sidtab_search_force(struct sidtab *s, u32 sid)
>>> +struct sidtab_entry *sidtab_search_entry_force(struct sidtab *s, u32 
>>> sid)
>>>   {
>>>       return sidtab_search_core(s, sid, 1);
>>>   }
>>> @@ -230,7 +257,7 @@ static int sidtab_rcache_search(struct sidtab *s, 
>>> struct context *context,
>>>           if (v >= SIDTAB_MAX)
>>>               continue;
>>> -        if (context_cmp(sidtab_do_lookup(s, v, 0), context)) {
>>> +        if (context_cmp(sidtab_lookup_unsafe(s, v), context)) {
>>>               sidtab_rcache_update(s, v, i);
>>>               *index = v;
>>>               return 0;
>>> @@ -245,7 +272,7 @@ static int sidtab_reverse_lookup(struct sidtab 
>>> *s, struct context *context,
>>>       unsigned long flags;
>>>       u32 count, count_locked, level, pos;
>>>       struct sidtab_convert_params *convert;
>>> -    struct context *dst, *dst_convert;
>>> +    struct sidtab_entry *dst, *dst_convert;
>>>       int rc;
>>>       rc = sidtab_rcache_search(s, context, index);
>>> @@ -273,7 +300,7 @@ static int sidtab_reverse_lookup(struct sidtab 
>>> *s, struct context *context,
>>>       /* if count has changed before we acquired the lock, then catch 
>>> up */
>>>       while (count < count_locked) {
>>> -        if (context_cmp(sidtab_do_lookup(s, count, 0), context)) {
>>> +        if (context_cmp(sidtab_lookup_unsafe(s, count), context)) {
>>>               sidtab_rcache_push(s, count);
>>>               *index = count;
>>>               rc = 0;
>>> @@ -293,7 +320,7 @@ static int sidtab_reverse_lookup(struct sidtab 
>>> *s, struct context *context,
>>>       if (!dst)
>>>           goto out_unlock;
>>> -    rc = context_cpy(dst, context);
>>> +    rc = context_cpy(&dst->context, context);
>>>       if (rc)
>>>           goto out_unlock;
>>> @@ -305,13 +332,14 @@ static int sidtab_reverse_lookup(struct sidtab 
>>> *s, struct context *context,
>>>           rc = -ENOMEM;
>>>           dst_convert = sidtab_do_lookup(convert->target, count, 1);
>>>           if (!dst_convert) {
>>> -            context_destroy(dst);
>>> +            context_destroy(&dst->context);
>>>               goto out_unlock;
>>>           }
>>> -        rc = convert->func(context, dst_convert, convert->args);
>>> +        rc = convert->func(context, &dst_convert->context,
>>> +                   convert->args);
>>>           if (rc) {
>>> -            context_destroy(dst);
>>> +            context_destroy(&dst->context);
>>>               goto out_unlock;
>>>           }
>>> @@ -341,9 +369,9 @@ int sidtab_context_to_sid(struct sidtab *s, 
>>> struct context *context, u32 *sid)
>>>       u32 i;
>>>       for (i = 0; i < SECINITSID_NUM; i++) {
>>> -        struct sidtab_isid_entry *entry = &s->isids[i];
>>> +        struct sidtab_isid_entry *isid = &s->isids[i];
>>> -        if (entry->set && context_cmp(context, &entry->context)) {
>>> +        if (isid->set && context_cmp(context, &isid->entry.context)) {
>>>               *sid = i + 1;
>>>               return 0;
>>>           }
>>> @@ -453,6 +481,14 @@ int sidtab_convert(struct sidtab *s, struct 
>>> sidtab_convert_params *params)
>>>       return rc;
>>>   }
>>> +static void sidtab_destroy_entry(struct sidtab_entry *entry)
>>> +{
>>> +    context_destroy(&entry->context);
>>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>>> +    kfree(entry->cache);
>>> +#endif
>>> +}
>>> +
>>>   static void sidtab_destroy_tree(union sidtab_entry_inner entry, u32 
>>> level)
>>>   {
>>>       u32 i;
>>> @@ -473,7 +509,7 @@ static void sidtab_destroy_tree(union 
>>> sidtab_entry_inner entry, u32 level)
>>>               return;
>>>           for (i = 0; i < SIDTAB_LEAF_ENTRIES; i++)
>>> -            context_destroy(&node->entries[i].context);
>>> +            sidtab_destroy_entry(&node->entries[i]);
>>>           kfree(node);
>>>       }
>>>   }
>>> @@ -484,7 +520,7 @@ void sidtab_destroy(struct sidtab *s)
>>>       for (i = 0; i < SECINITSID_NUM; i++)
>>>           if (s->isids[i].set)
>>> -            context_destroy(&s->isids[i].context);
>>> +            sidtab_destroy_entry(&s->isids[i].entry);
>>>       level = SIDTAB_MAX_LEVEL;
>>>       while (level && !s->roots[level].ptr_inner)
>>> @@ -492,3 +528,87 @@ void sidtab_destroy(struct sidtab *s)
>>>       sidtab_destroy_tree(s->roots[level], level);
>>>   }
>>> +
>>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>>> +
>>> +void sidtab_sid2str_put(struct sidtab *s, struct sidtab_entry *entry,
>>> +            const char *str, u32 str_len)
>>> +{
>>> +    struct sidtab_str_cache *cache, *victim;
>>> +
>>> +    /* do not cache invalid contexts */
>>> +    if (entry->context.len)
>>> +        return;
>>> +
>>> +    /*
>>> +     * Skip the put operation when in non-task context to avoid the 
>>> need
>>> +     * to disable interrupts while holding s->cache_lock.
>>> +     */
>>> +    if (!in_task())
>>> +        return;
>>> +
>>> +    spin_lock(&s->cache_lock);
>>> +
>>> +    if (entry->cache) {
>>> +        /* entry in cache - just bump to he head of LRU list */
>>> +        list_move(&entry->cache->lru_member, &s->cache_lru_list);
>>> +        goto out_unlock;
>>> +    }
>>> +
>>> +    cache = kmalloc(sizeof(struct sidtab_str_cache) + str_len, 
>>> GFP_ATOMIC);
>>> +    if (!cache)
>>> +        goto out_unlock;
>>> +
>>> +    if (s->cache_free_slots == 0) {
>>> +        /* pop a cache entry from the tail and free it */
>>> +        victim = container_of(s->cache_lru_list.prev,
>>> +                      struct sidtab_str_cache, lru_member);
>>> +        list_del(&victim->lru_member);
>>> +        kfree_rcu(victim, rcu_member);
>>> +        rcu_assign_pointer(victim->parent->cache, NULL);
>>> +    } else {
>>> +        s->cache_free_slots--;
>>> +    }
>>> +    cache->parent = entry;
>>> +    cache->len = str_len;
>>> +    memcpy(cache->str, str, str_len);
>>> +    rcu_head_init(&cache->rcu_member);
>>> +    list_add(&cache->lru_member, &s->cache_lru_list);
>>> +
>>> +    rcu_assign_pointer(entry->cache, cache);
>>> +
>>> +out_unlock:
>>> +    spin_unlock(&s->cache_lock);
>>> +}
>>> +
>>> +int sidtab_sid2str_get(struct sidtab *s, struct sidtab_entry *entry,
>>> +               char **out, u32 *out_len)
>>> +{
>>> +    struct sidtab_str_cache *cache;
>>> +    int rc = 0;
>>> +
>>> +    if (entry->context.len)
>>> +        return -ENOENT; /* do not cache invalid contexts */
>>> +
>>> +    rcu_read_lock();
>>> +
>>> +    cache = rcu_dereference(entry->cache);
>>> +    if (!cache) {
>>> +        rc = -ENOENT;
>>> +    } else {
>>> +        *out_len = cache->len;
>>> +        if (out) {
>>> +            *out = kmemdup(cache->str, cache->len, GFP_ATOMIC);
>>> +            if (!*out)
>>> +                rc = -ENOMEM;
>>> +        }
>>> +    }
>>> +
>>> +    rcu_read_unlock();
>>> +
>>> +    if (!rc && out)
>>> +        sidtab_sid2str_put(s, entry, *out, *out_len);
>>> +    return rc;
>>> +}
>>> +
>>> +#endif /* CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0 */
>>> diff --git a/security/selinux/ss/sidtab.h b/security/selinux/ss/sidtab.h
>>> index 1f4763141aa1..9159a300bde3 100644
>>> --- a/security/selinux/ss/sidtab.h
>>> +++ b/security/selinux/ss/sidtab.h
>>> @@ -16,13 +16,13 @@
>>>   #include "context.h"
>>> -struct sidtab_entry_leaf {
>>> +struct sidtab_entry {
>>>       struct context context;
>>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>>> +    struct sidtab_str_cache *cache;
>>> +#endif
>>>   };
>>> -struct sidtab_node_inner;
>>> -struct sidtab_node_leaf;
>>> -
>>>   union sidtab_entry_inner {
>>>       struct sidtab_node_inner *ptr_inner;
>>>       struct sidtab_node_leaf  *ptr_leaf;
>>> @@ -38,7 +38,7 @@ union sidtab_entry_inner {
>>>       (SIDTAB_NODE_ALLOC_SHIFT - size_to_shift(sizeof(union 
>>> sidtab_entry_inner)))
>>>   #define SIDTAB_INNER_ENTRIES ((size_t)1 << SIDTAB_INNER_SHIFT)
>>>   #define SIDTAB_LEAF_ENTRIES \
>>> -    (SIDTAB_NODE_ALLOC_SIZE / sizeof(struct sidtab_entry_leaf))
>>> +    (SIDTAB_NODE_ALLOC_SIZE / sizeof(struct sidtab_entry))
>>>   #define SIDTAB_MAX_BITS 32
>>>   #define SIDTAB_MAX U32_MAX
>>> @@ -48,7 +48,7 @@ union sidtab_entry_inner {
>>>                SIDTAB_INNER_SHIFT)
>>>   struct sidtab_node_leaf {
>>> -    struct sidtab_entry_leaf entries[SIDTAB_LEAF_ENTRIES];
>>> +    struct sidtab_entry entries[SIDTAB_LEAF_ENTRIES];
>>>   };
>>>   struct sidtab_node_inner {
>>> @@ -57,7 +57,7 @@ struct sidtab_node_inner {
>>>   struct sidtab_isid_entry {
>>>       int set;
>>> -    struct context context;
>>> +    struct sidtab_entry entry;
>>>   };
>>>   struct sidtab_convert_params {
>>> @@ -83,6 +83,13 @@ struct sidtab {
>>>       struct sidtab_convert_params *convert;
>>>       spinlock_t lock;
>>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>>> +    /* SID -> context string cache */
>>> +    u32 cache_free_slots;
>>> +    struct list_head cache_lru_list;
>>> +    spinlock_t cache_lock;
>>> +#endif
>>> +
>>>       /* reverse lookup cache - access atomically via 
>>> {READ|WRITE}_ONCE() */
>>>       u32 rcache[SIDTAB_RCACHE_SIZE];
>>> @@ -92,8 +99,22 @@ struct sidtab {
>>>   int sidtab_init(struct sidtab *s);
>>>   int sidtab_set_initial(struct sidtab *s, u32 sid, struct context 
>>> *context);
>>> -struct context *sidtab_search(struct sidtab *s, u32 sid);
>>> -struct context *sidtab_search_force(struct sidtab *s, u32 sid);
>>> +struct sidtab_entry *sidtab_search_entry(struct sidtab *s, u32 sid);
>>> +struct sidtab_entry *sidtab_search_entry_force(struct sidtab *s, u32 
>>> sid);
>>> +
>>> +static inline struct context *sidtab_search(struct sidtab *s, u32 sid)
>>> +{
>>> +    struct sidtab_entry *entry = sidtab_search_entry(s, sid);
>>> +
>>> +    return entry ? &entry->context : NULL;
>>> +}
>>> +
>>> +static inline struct context *sidtab_search_force(struct sidtab *s, 
>>> u32 sid)
>>> +{
>>> +    struct sidtab_entry *entry = sidtab_search_entry_force(s, sid);
>>> +
>>> +    return entry ? &entry->context : NULL;
>>> +}
>>>   int sidtab_convert(struct sidtab *s, struct sidtab_convert_params 
>>> *params);
>>> @@ -101,6 +122,25 @@ int sidtab_context_to_sid(struct sidtab *s, 
>>> struct context *context, u32 *sid);
>>>   void sidtab_destroy(struct sidtab *s);
>>> +#if CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0
>>> +void sidtab_sid2str_put(struct sidtab *s, struct sidtab_entry *entry,
>>> +            const char *str, u32 str_len);
>>> +int sidtab_sid2str_get(struct sidtab *s, struct sidtab_entry *entry,
>>> +               char **out, u32 *out_len);
>>> +#else
>>> +static inline void sidtab_sid2str_put(struct sidtab *s,
>>> +                      struct sidtab_entry *entry,
>>> +                      const char *str, u32 str_len)
>>> +{
>>> +}
>>> +static inline int sidtab_sid2str_get(struct sidtab *s,
>>> +                     struct sidtab_entry *entry,
>>> +                     char **out, u32 *out_len)
>>> +{
>>> +    return -ENOENT;
>>> +}
>>> +#endif /* CONFIG_SECURITY_SELINUX_SID2STR_CACHE_SIZE > 0 */
>>> +
>>>   #endif    /* _SS_SIDTAB_H_ */
>>>
>>
>

Ondrej Mosnacek Nov. 7, 2019, 12:41 p.m. UTC | #4

On Wed, Nov 6, 2019 at 8:48 PM Stephen Smalley <sds@tycho.nsa.gov> wrote:
> On 11/6/19 2:22 PM, Stephen Smalley wrote:
> > On 11/6/19 11:11 AM, Stephen Smalley wrote:
> >> On 11/6/19 3:26 AM, Ondrej Mosnacek wrote:
> >>> Translating a context struct to string can be quite slow, especially if
> >>> the context has a lot of category bits set. This can cause quite
> >>> noticeable performance impact in situations where the translation needs
> >>> to be done repeatedly. A common example is a UNIX datagram socket with
> >>> the SO_PASSSEC option enabled, which is used e.g. by systemd-journald
> >>> when receiving log messages via datagram socket. This scenario can be
> >>> reproduced with:
> >>>
> >>>      cat /dev/urandom | base64 | logger &
> >>>      timeout 30s perf record -p $(pidof systemd-journald) -a -g
> >>>      kill %1
> >>>      perf report -g none --pretty raw | grep security_secid_to_secctx
> >>>
> >>> Before the caching introduced by this patch, computing the context
> >>> string (security_secid_to_secctx() function) takes up ~65% of
> >>> systemd-journald's CPU time (assuming a context with 1024 categories
> >>> set and Fedora x86_64 release kernel configs). After this patch
> >>> (assuming near-perfect cache hit ratio) this overhead is reduced to just
> >>> ~2%.
> >>>
> >>> This patch addresses the issue by caching a certain number (compile-time
> >>> configurable) of recently used context strings to speed up repeated
> >>> translations of the same context, while using only a small amount of
> >>> memory.
> >>>
> >>> The cache is integrated into the existing sidtab table by adding a field
> >>> to each entry, which when not NULL contains an RCU-protected pointer to
> >>> a cache entry containing the cached string. The cache entries are kept
> >>> in a linked list sorted according to how recently they were used. On a
> >>> cache miss when the cache is full, the least recently used entry is
> >>> removed to make space for the new entry.
> >>>
> >>> The patch migrates security_sid_to_context_core() to use the cache (also
> >>> a few other functions where it was possible without too much fuss, but
> >>> these mostly use the translation for logging in case of error, which is
> >>> rare).
> >>>
> >>> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1733259
> >>> Cc: Michal Sekletar <msekleta@redhat.com>
> >>> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> >>
> >> This looks good to me and didn't trigger any issues during testing.
> >> Might want to run it by the RCU wizards, e.g. Paul McKenney, to
> >> confirm that it is correct and optimal usage of RCU.  I didn't see
> >> anywhere near the same degree of performance improvement in running
> >> your reproducer above but I also have all the kernel debugging options
> >> enabled so perhaps those are creating noise or perhaps the reproducer
> >> doesn't yield stable results.
> >
> > Rebuilding with the stock Fedora x86_64 kernel config was closer to your
> > results albeit still different, ~35% before and ~2% after.
>
> Ah, I can reproduce your ~65% result on the 5.3-based Fedora kernel, but
> not with mainline 5.4.0-rc1.  Only SELinux change between those two that
> seems potentially relevant is your "selinux: avoid atomic_t usage in
> sidtab" patch.

Hm... did you use the stock Fedora kernel RPM as the baseline? If so,
this could be because on stable Fedora releases the kernel package is
built with release config and kernel-debug with debug config, while on
Rawhide there is only one kernel package, which is built with debug
config. Under debug Fedora config the numbers are completely different
due to the overhead of various debug checks. I don't remember the
"after" value that I got when testing the patched Rawhide kernel with
the default debug config, but on stock Rawhide I got 43%, and on
Rawhide kernel rebuild with release config I got 65% again.

--
Ondrej Mosnacek <omosnace at redhat dot com>
Software Engineer, Security Technologies
Red Hat, Inc.

Stephen Smalley Nov. 7, 2019, 5:59 p.m. UTC | #5

On 11/7/19 7:41 AM, Ondrej Mosnacek wrote:
> On Wed, Nov 6, 2019 at 8:48 PM Stephen Smalley <sds@tycho.nsa.gov> wrote:
>> On 11/6/19 2:22 PM, Stephen Smalley wrote:
>>> On 11/6/19 11:11 AM, Stephen Smalley wrote:
>>>> On 11/6/19 3:26 AM, Ondrej Mosnacek wrote:
>>>>> Translating a context struct to string can be quite slow, especially if
>>>>> the context has a lot of category bits set. This can cause quite
>>>>> noticeable performance impact in situations where the translation needs
>>>>> to be done repeatedly. A common example is a UNIX datagram socket with
>>>>> the SO_PASSSEC option enabled, which is used e.g. by systemd-journald
>>>>> when receiving log messages via datagram socket. This scenario can be
>>>>> reproduced with:
>>>>>
>>>>>       cat /dev/urandom | base64 | logger &
>>>>>       timeout 30s perf record -p $(pidof systemd-journald) -a -g
>>>>>       kill %1
>>>>>       perf report -g none --pretty raw | grep security_secid_to_secctx
>>>>>
>>>>> Before the caching introduced by this patch, computing the context
>>>>> string (security_secid_to_secctx() function) takes up ~65% of
>>>>> systemd-journald's CPU time (assuming a context with 1024 categories
>>>>> set and Fedora x86_64 release kernel configs). After this patch
>>>>> (assuming near-perfect cache hit ratio) this overhead is reduced to just
>>>>> ~2%.
>>>>>
>>>>> This patch addresses the issue by caching a certain number (compile-time
>>>>> configurable) of recently used context strings to speed up repeated
>>>>> translations of the same context, while using only a small amount of
>>>>> memory.
>>>>>
>>>>> The cache is integrated into the existing sidtab table by adding a field
>>>>> to each entry, which when not NULL contains an RCU-protected pointer to
>>>>> a cache entry containing the cached string. The cache entries are kept
>>>>> in a linked list sorted according to how recently they were used. On a
>>>>> cache miss when the cache is full, the least recently used entry is
>>>>> removed to make space for the new entry.
>>>>>
>>>>> The patch migrates security_sid_to_context_core() to use the cache (also
>>>>> a few other functions where it was possible without too much fuss, but
>>>>> these mostly use the translation for logging in case of error, which is
>>>>> rare).
>>>>>
>>>>> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1733259
>>>>> Cc: Michal Sekletar <msekleta@redhat.com>
>>>>> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
>>>>
>>>> This looks good to me and didn't trigger any issues during testing.
>>>> Might want to run it by the RCU wizards, e.g. Paul McKenney, to
>>>> confirm that it is correct and optimal usage of RCU.  I didn't see
>>>> anywhere near the same degree of performance improvement in running
>>>> your reproducer above but I also have all the kernel debugging options
>>>> enabled so perhaps those are creating noise or perhaps the reproducer
>>>> doesn't yield stable results.
>>>
>>> Rebuilding with the stock Fedora x86_64 kernel config was closer to your
>>> results albeit still different, ~35% before and ~2% after.
>>
>> Ah, I can reproduce your ~65% result on the 5.3-based Fedora kernel, but
>> not with mainline 5.4.0-rc1.  Only SELinux change between those two that
>> seems potentially relevant is your "selinux: avoid atomic_t usage in
>> sidtab" patch.
> 
> Hm... did you use the stock Fedora kernel RPM as the baseline? If so,
> this could be because on stable Fedora releases the kernel package is
> built with release config and kernel-debug with debug config, while on
> Rawhide there is only one kernel package, which is built with debug
> config. Under debug Fedora config the numbers are completely different
> due to the overhead of various debug checks. I don't remember the
> "after" value that I got when testing the patched Rawhide kernel with
> the default debug config, but on stock Rawhide I got 43%, and on
> Rawhide kernel rebuild with release config I got 65% again.

I first built selinux/next (based on 5.4-rc1) before and after your 
patch using a config with many debug options enabled (including KASAN), 
which yielded wildly different percentages both before and after - don't 
remember the exact values (but still improved by your patch).

Then I built the same sources using the stock Fedora 31 release kernel 
config and got the 35% versus 2% figures, likewise an improvement.

Then I ran your reproducer just on the stock Fedora 31 release kernel, 
which happened to be 5.3-based, and got the 65% versus 2% figures that 
matched your results.  So I'm not sure what accounts for the difference 
in the before results between the stock Fedora 31 release kernel and 
selinux/next using the same config.  Could be a 5.3 vs 5.4-rc1 change, a 
change in selinux/next on top of 5.4-rc1, or something different in the 
build toolchain/environment used for the stock Fedora kernel versus my 
build host (which was running Fedora 31).

Regardless, I do see a significant improvement in all cases from the 
patch, only the degree of improvement differs.  So I'm fine with it. 
Might want to get a 2nd opinion from Paul McKenney all the same on the 
RCU bits.

[v2] selinux: cache the SID -> context string translation

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