@@ -1134,6 +1134,7 @@ struct bpf_attach_target_info {
struct module *tgt_mod;
const char *tgt_name;
const struct btf_type *tgt_type;
+ bool is_lsm_target;
};
#define BPF_DISPATCHER_MAX 48 /* Fits in 2048B */
@@ -29,6 +29,7 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
bool bpf_lsm_is_sleepable_hook(u32 btf_id);
bool bpf_lsm_is_trusted(const struct bpf_prog *prog);
+void bpf_lsm_toggle_hook(void *addr, bool value);
static inline struct bpf_storage_blob *bpf_inode(
const struct inode *inode)
@@ -78,6 +79,10 @@ static inline void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog,
{
}
+static inline void bpf_lsm_toggle_hook(void *addr, bool value)
+{
+}
+
#endif /* CONFIG_BPF_LSM */
#endif /* _LINUX_BPF_LSM_H */
@@ -96,11 +96,14 @@ struct lsm_static_calls_table {
* @scalls: The beginning of the array of static calls assigned to this hook.
* @hook: The callback for the hook.
* @lsm: The name of the lsm that owns this hook.
+ * @default_state: The state of the LSM hook when initialized. If set to false,
+ * the static key guarding the hook will be set to disabled.
*/
struct security_hook_list {
struct lsm_static_call *scalls;
union security_list_options hook;
const char *lsm;
+ bool default_state;
} __randomize_layout;
/*
@@ -131,7 +134,15 @@ struct lsm_blob_sizes {
#define LSM_HOOK_INIT(NAME, CALLBACK) \
{ \
.scalls = static_calls_table.NAME, \
- .hook = { .NAME = CALLBACK } \
+ .hook = { .NAME = CALLBACK }, \
+ .default_state = true \
+ }
+
+#define LSM_HOOK_INIT_DISABLED(NAME, CALLBACK) \
+ { \
+ .scalls = static_calls_table.NAME, \
+ .hook = { .NAME = CALLBACK }, \
+ .default_state = false \
}
extern char *lsm_names;
@@ -13,6 +13,7 @@
#include <linux/bpf_verifier.h>
#include <linux/bpf_lsm.h>
#include <linux/delay.h>
+#include <linux/bpf_lsm.h>
/* dummy _ops. The verifier will operate on target program's ops. */
const struct bpf_verifier_ops bpf_extension_verifier_ops = {
@@ -514,7 +515,7 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_tr
{
enum bpf_tramp_prog_type kind;
struct bpf_tramp_link *link_exiting;
- int err = 0;
+ int err = 0, num_lsm_progs = 0;
int cnt = 0, i;
kind = bpf_attach_type_to_tramp(link->link.prog);
@@ -545,8 +546,14 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_tr
continue;
/* prog already linked */
return -EBUSY;
+
+ if (link_exiting->link.prog->type == BPF_PROG_TYPE_LSM)
+ num_lsm_progs++;
}
+ if (!num_lsm_progs && link->link.prog->type == BPF_PROG_TYPE_LSM)
+ bpf_lsm_toggle_hook(tr->func.addr, true);
+
hlist_add_head(&link->tramp_hlist, &tr->progs_hlist[kind]);
tr->progs_cnt[kind]++;
err = bpf_trampoline_update(tr, true /* lock_direct_mutex */);
@@ -569,8 +576,10 @@ int bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline
static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr)
{
+ struct bpf_tramp_link *link_exiting;
enum bpf_tramp_prog_type kind;
- int err;
+ bool lsm_link_found = false;
+ int err, num_lsm_progs = 0;
kind = bpf_attach_type_to_tramp(link->link.prog);
if (kind == BPF_TRAMP_REPLACE) {
@@ -580,8 +589,24 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_
tr->extension_prog = NULL;
return err;
}
+
+ if (link->link.prog->type == BPF_PROG_TYPE_LSM) {
+ hlist_for_each_entry(link_exiting, &tr->progs_hlist[kind],
+ tramp_hlist) {
+ if (link_exiting->link.prog->type == BPF_PROG_TYPE_LSM)
+ num_lsm_progs++;
+
+ if (link_exiting->link.prog == link->link.prog)
+ lsm_link_found = true;
+ }
+ }
+
hlist_del_init(&link->tramp_hlist);
tr->progs_cnt[kind]--;
+
+ if (lsm_link_found && num_lsm_progs == 1)
+ bpf_lsm_toggle_hook(tr->func.addr, false);
+
return bpf_trampoline_update(tr, true /* lock_direct_mutex */);
}
@@ -8,7 +8,7 @@
static struct security_hook_list bpf_lsm_hooks[] __ro_after_init = {
#define LSM_HOOK(RET, DEFAULT, NAME, ...) \
- LSM_HOOK_INIT(NAME, bpf_lsm_##NAME),
+ LSM_HOOK_INIT_DISABLED(NAME, bpf_lsm_##NAME),
#include <linux/lsm_hook_defs.h>
#undef LSM_HOOK
LSM_HOOK_INIT(inode_free_security, bpf_inode_storage_free),
@@ -32,3 +32,26 @@ DEFINE_LSM(bpf) = {
.init = bpf_lsm_init,
.blobs = &bpf_lsm_blob_sizes
};
+
+void bpf_lsm_toggle_hook(void *addr, bool value)
+{
+ struct lsm_static_call *scalls;
+ struct security_hook_list *h;
+ int i, j;
+
+ for (i = 0; i < ARRAY_SIZE(bpf_lsm_hooks); i++) {
+ h = &bpf_lsm_hooks[i];
+ scalls = h->scalls;
+ if (h->hook.lsm_callback == addr)
+ continue;
+
+ for (j = 0; j < MAX_LSM_COUNT; j++) {
+ if (scalls[j].hl != h)
+ continue;
+ if (value)
+ static_branch_enable(scalls[j].active);
+ else
+ static_branch_disable(scalls[j].active);
+ }
+ }
+}
@@ -374,7 +374,8 @@ static void __init lsm_static_call_init(struct security_hook_list *hl)
__static_call_update(scall->key, scall->trampoline,
hl->hook.lsm_callback);
scall->hl = hl;
- static_branch_enable(scall->active);
+ if (hl->default_state)
+ static_branch_enable(scall->active);
return;
}
scall++;
BPF LSM hooks have side-effects (even when a default value is returned), as some hooks end up behaving differently due to the very presence of the hook. The static keys guarding the BPF LSM hooks are disabled by default and enabled only when a BPF program is attached implementing the hook logic. This avoids the issue of the side-effects and also the minor overhead associated with the empty callback. security_file_ioctl: 0xffffffff818f0e30 <+0>: endbr64 0xffffffff818f0e34 <+4>: nopl 0x0(%rax,%rax,1) 0xffffffff818f0e39 <+9>: push %rbp 0xffffffff818f0e3a <+10>: push %r14 0xffffffff818f0e3c <+12>: push %rbx 0xffffffff818f0e3d <+13>: mov %rdx,%rbx 0xffffffff818f0e40 <+16>: mov %esi,%ebp 0xffffffff818f0e42 <+18>: mov %rdi,%r14 0xffffffff818f0e45 <+21>: jmp 0xffffffff818f0e57 <security_file_ioctl+39> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Static key enabled for SELinux 0xffffffff818f0e47 <+23>: xchg %ax,%ax ^^^^^^^^^^^^^^ Static key disabled for BPF. This gets patched when a BPF LSM program is attached 0xffffffff818f0e49 <+25>: xor %eax,%eax 0xffffffff818f0e4b <+27>: xchg %ax,%ax 0xffffffff818f0e4d <+29>: pop %rbx 0xffffffff818f0e4e <+30>: pop %r14 0xffffffff818f0e50 <+32>: pop %rbp 0xffffffff818f0e51 <+33>: cs jmp 0xffffffff82c00000 <__x86_return_thunk> 0xffffffff818f0e57 <+39>: endbr64 0xffffffff818f0e5b <+43>: mov %r14,%rdi 0xffffffff818f0e5e <+46>: mov %ebp,%esi 0xffffffff818f0e60 <+48>: mov %rbx,%rdx 0xffffffff818f0e63 <+51>: call 0xffffffff819033c0 <selinux_file_ioctl> 0xffffffff818f0e68 <+56>: test %eax,%eax 0xffffffff818f0e6a <+58>: jne 0xffffffff818f0e4d <security_file_ioctl+29> 0xffffffff818f0e6c <+60>: jmp 0xffffffff818f0e47 <security_file_ioctl+23> 0xffffffff818f0e6e <+62>: endbr64 0xffffffff818f0e72 <+66>: mov %r14,%rdi 0xffffffff818f0e75 <+69>: mov %ebp,%esi 0xffffffff818f0e77 <+71>: mov %rbx,%rdx 0xffffffff818f0e7a <+74>: call 0xffffffff8141e3b0 <bpf_lsm_file_ioctl> 0xffffffff818f0e7f <+79>: test %eax,%eax 0xffffffff818f0e81 <+81>: jne 0xffffffff818f0e4d <security_file_ioctl+29> 0xffffffff818f0e83 <+83>: jmp 0xffffffff818f0e49 <security_file_ioctl+25> 0xffffffff818f0e85 <+85>: endbr64 0xffffffff818f0e89 <+89>: mov %r14,%rdi 0xffffffff818f0e8c <+92>: mov %ebp,%esi 0xffffffff818f0e8e <+94>: mov %rbx,%rdx 0xffffffff818f0e91 <+97>: pop %rbx 0xffffffff818f0e92 <+98>: pop %r14 0xffffffff818f0e94 <+100>: pop %rbp 0xffffffff818f0e95 <+101>: ret Signed-off-by: KP Singh <kpsingh@kernel.org> --- include/linux/bpf.h | 1 + include/linux/bpf_lsm.h | 5 +++++ include/linux/lsm_hooks.h | 13 ++++++++++++- kernel/bpf/trampoline.c | 29 +++++++++++++++++++++++++++-- security/bpf/hooks.c | 25 ++++++++++++++++++++++++- security/security.c | 3 ++- 6 files changed, 71 insertions(+), 5 deletions(-)