diff mbox series

[v16,17/20] ipe: enable support for fs-verity as a trust provider

Message ID 1711657047-10526-18-git-send-email-wufan@linux.microsoft.com (mailing list archive)
State Superseded, archived
Delegated to: Mike Snitzer
Headers show
Series Integrity Policy Enforcement LSM (IPE) | expand

Commit Message

Fan Wu March 28, 2024, 8:17 p.m. UTC 
Enable IPE policy authors to indicate trust for a singular fsverity
file, identified by the digest information, through "fsverity_digest"
and all files using fsverity's builtin signatures via
"fsverity_signature".

This enables file-level integrity claims to be expressed in IPE,
allowing individual files to be authorized, giving some flexibility
for policy authors. Such file-level claims are important to be expressed
for enforcing the integrity of packages, as well as address some of the
scalability issues in a sole dm-verity based solution (# of loop back
devices, etc).

This solution cannot be done in userspace as the minimum threat that
IPE should mitigate is an attacker downloads malicious payload with
all required dependencies. These dependencies can lack the userspace
check, bypassing the protection entirely. A similar attack succeeds if
the userspace component is replaced with a version that does not
perform the check. As a result, this can only be done in the common
entry point - the kernel.

Signed-off-by: Deven Bowers <deven.desai@linux.microsoft.com>
Signed-off-by: Fan Wu <wufan@linux.microsoft.com>

---
v1-v6:
  + Not present

v7:
  Introduced

v8:
  * Undo squash of 08/12, 10/12 - separating drivers/md/ from security/
  * Use common-audit function for fsverity_signature.
  + Change fsverity implementation to use fsverity_get_digest
  + prevent unnecessary copy of fs-verity signature data, instead
    just check for presence of signature data.
  + Remove free_inode_security hook, as the digest is now acquired
    at runtime instead of via LSM blob.

v9:
  + Adapt to the new parser

v10:
  + Update the fsverity get digest call

v11:
  + No changes

v12:
  + Fix audit format
  + Simplify property evaluation

v13:
  + Remove the CONFIG_IPE_PROP_FS_VERITY dependency inside the parser
    to make the policy grammar independent of the kernel config.

v14:
  + No changes

v15:
  + Fix on grammar issue in Kconfig
  + Switch hook to security_inode_setintegrity()

v16:
  + Rewrite fsverity signature part in Kconfig
---
 security/ipe/Kconfig         |  14 +++++
 security/ipe/audit.c         |  17 ++++++
 security/ipe/eval.c          | 108 ++++++++++++++++++++++++++++++++++-
 security/ipe/eval.h          |  10 ++++
 security/ipe/hooks.c         |  28 +++++++++
 security/ipe/hooks.h         |   6 ++
 security/ipe/ipe.c           |  13 +++++
 security/ipe/ipe.h           |   3 +
 security/ipe/policy.h        |   3 +
 security/ipe/policy_parser.c |   6 ++
 10 files changed, 207 insertions(+), 1 deletion(-)

Comments

Eric Biggers April 3, 2024, 5:10 a.m. UTC | #1 
On Thu, Mar 28, 2024 at 01:17:24PM -0700, Fan Wu wrote:
> Enable IPE policy authors to indicate trust for a singular fsverity
> file, identified by the digest information, through "fsverity_digest"
> and all files using fsverity's builtin signatures via
> "fsverity_signature".

Again, I'm pretty sure you actually care about all files with *valid* builtin
signatures, not simply all files with builtin signatures...

> +/**
> + * ipe_inode_setintegrity - save integrity data from a inode to IPE's LSM blob.
> + * @inode: The inode to source the security blob from.
> + * @type: Supplies the integrity type.
> + * @value: The value to be stored.
> + * @size: The size of @value.
> + *
> + * Saves fsverity signature into inode security blob
> + *
> + * Return:
> + * * 0	- OK
> + * * !0	- Error
> + */
> +int ipe_inode_setintegrity(struct inode *inode, enum lsm_integrity_type type,
> +			   const void *value, size_t size)
> +{
> +	struct ipe_inode *inode_sec = ipe_inode(inode);
> +
> +	if (type == LSM_INT_FSVERITY_BUILTINSIG) {
> +		inode_sec->fs_verity_signed = size > 0 && value;
> +		return 0;
> +	}
> +
> +	return 0;

This is the actual code, and it's *still* documented incorrectly.  No, it
doesn't "Save fsverity signature into inode security blob".  All it actually
does is save a flag saying that there was a valid signature.

The flag also should be called something like fsverity_sig_valid, indicating
that there is a builtin signature *and* it's valid.

- Eric
diff mbox series

Patch

diff --git a/security/ipe/Kconfig b/security/ipe/Kconfig
index 5433ca3fc855..1b3159c0e129 100644
--- a/security/ipe/Kconfig
+++ b/security/ipe/Kconfig
@@ -30,6 +30,20 @@  config IPE_PROP_DM_VERITY
 	  that was mounted with a signed root-hash or the volume's
 	  root hash matches the supplied value in the policy.
 
+	  If unsure, answer Y.
+
+config IPE_PROP_FS_VERITY
+	bool "Enable property for fs-verity files"
+	depends on FS_VERITY && FS_VERITY_BUILTIN_SIGNATURES
+	help
+	  This option enables the usage of properties "fsverity_signature"
+	  and "fsverity_digest". These properties evaluate to TRUE when
+	  a file is fsverity enabled and has a valid builtin signature
+	  whose signing cert is in the .fs-verity keyring or its
+	  digest matches the supplied value in the policy.
+
+	  if unsure, answer Y.
+
 endmenu
 
 endif
diff --git a/security/ipe/audit.c b/security/ipe/audit.c
index 3acbfecc9f43..f508944a3ed1 100644
--- a/security/ipe/audit.c
+++ b/security/ipe/audit.c
@@ -53,6 +53,9 @@  static const char *const audit_prop_names[__IPE_PROP_MAX] = {
 	"dmverity_roothash=",
 	"dmverity_signature=FALSE",
 	"dmverity_signature=TRUE",
+	"fsverity_digest=",
+	"fsverity_signature=FALSE",
+	"fsverity_signature=TRUE",
 };
 
 /**
@@ -66,6 +69,17 @@  static void audit_dmv_roothash(struct audit_buffer *ab, const void *rh)
 	ipe_digest_audit(ab, rh);
 }
 
+/**
+ * audit_fsv_digest - audit the digest of a fsverity_digest property.
+ * @ab: Supplies a pointer to the audit_buffer to append to.
+ * @d: Supplies a pointer to the digest structure.
+ */
+static void audit_fsv_digest(struct audit_buffer *ab, const void *d)
+{
+	audit_log_format(ab, "%s", audit_prop_names[IPE_PROP_FSV_DIGEST]);
+	ipe_digest_audit(ab, d);
+}
+
 /**
  * audit_rule - audit an IPE policy rule approximation.
  * @ab: Supplies a pointer to the audit_buffer to append to.
@@ -82,6 +96,9 @@  static void audit_rule(struct audit_buffer *ab, const struct ipe_rule *r)
 		case IPE_PROP_DMV_ROOTHASH:
 			audit_dmv_roothash(ab, ptr->value);
 			break;
+		case IPE_PROP_FSV_DIGEST:
+			audit_fsv_digest(ab, ptr->value);
+			break;
 		default:
 			audit_log_format(ab, "%s", audit_prop_names[ptr->type]);
 			break;
diff --git a/security/ipe/eval.c b/security/ipe/eval.c
index 8dcf7809c9fc..8cb8c64221e0 100644
--- a/security/ipe/eval.c
+++ b/security/ipe/eval.c
@@ -10,6 +10,7 @@ 
 #include <linux/sched.h>
 #include <linux/rcupdate.h>
 #include <linux/moduleparam.h>
+#include <linux/fsverity.h>
 
 #include "ipe.h"
 #include "eval.h"
@@ -51,6 +52,23 @@  static void build_ipe_bdev_ctx(struct ipe_eval_ctx *ctx, const struct inode *con
 }
 #endif /* CONFIG_IPE_PROP_DM_VERITY */
 
+#ifdef CONFIG_IPE_PROP_FS_VERITY
+/**
+ * build_ipe_inode_ctx - Build inode fields of an evaluation context.
+ * @ctx: Supplies a pointer to the context to be populated.
+ * @ino: Supplies the inode struct of the file triggered IPE event.
+ */
+static void build_ipe_inode_ctx(struct ipe_eval_ctx *ctx, const struct inode *const ino)
+{
+	ctx->ino = ino;
+	ctx->ipe_inode = ipe_inode(ctx->ino);
+}
+#else
+static void build_ipe_inode_ctx(struct ipe_eval_ctx *ctx, const struct inode *const ino)
+{
+}
+#endif /* CONFIG_IPE_PROP_FS_VERITY */
+
 /**
  * build_eval_ctx - Build an evaluation context.
  * @ctx: Supplies a pointer to the context to be populated.
@@ -63,13 +81,17 @@  void build_eval_ctx(struct ipe_eval_ctx *ctx,
 		    enum ipe_op_type op,
 		    enum ipe_hook_type hook)
 {
+	struct inode *ino;
+
 	ctx->file = file;
 	ctx->op = op;
 	ctx->hook = hook;
 
 	if (file) {
 		build_ipe_sb_ctx(ctx, file);
-		build_ipe_bdev_ctx(ctx, d_real_inode(file->f_path.dentry));
+		ino = d_real_inode(file->f_path.dentry);
+		build_ipe_bdev_ctx(ctx, ino);
+		build_ipe_inode_ctx(ctx, ino);
 	}
 }
 
@@ -148,6 +170,84 @@  static bool evaluate_dmv_sig_true(const struct ipe_eval_ctx *const ctx)
 }
 #endif /* CONFIG_IPE_PROP_DM_VERITY */
 
+#ifdef CONFIG_IPE_PROP_FS_VERITY
+/**
+ * evaluate_fsv_digest - Analyze @ctx against a fsv digest property.
+ * @ctx: Supplies a pointer to the context being evaluated.
+ * @p: Supplies a pointer to the property being evaluated.
+ *
+ * Return:
+ * * true	- The current @ctx match the @p
+ * * false	- The current @ctx doesn't match the @p
+ */
+static bool evaluate_fsv_digest(const struct ipe_eval_ctx *const ctx,
+				struct ipe_prop *p)
+{
+	enum hash_algo alg;
+	u8 digest[FS_VERITY_MAX_DIGEST_SIZE];
+	struct digest_info info;
+
+	if (!ctx->ino)
+		return false;
+	if (!fsverity_get_digest((struct inode *)ctx->ino,
+				 digest,
+				 NULL,
+				 &alg))
+		return false;
+
+	info.alg = hash_algo_name[alg];
+	info.digest = digest;
+	info.digest_len = hash_digest_size[alg];
+
+	return ipe_digest_eval(p->value, &info);
+}
+
+/**
+ * evaluate_fsv_sig_false - Analyze @ctx against a fsv sig false property.
+ * @ctx: Supplies a pointer to the context being evaluated.
+ *
+ * Return:
+ * * true	- The current @ctx match the property
+ * * false	- The current @ctx doesn't match the property
+ */
+static bool evaluate_fsv_sig_false(const struct ipe_eval_ctx *const ctx)
+{
+	return !ctx->ino ||
+	       !IS_VERITY(ctx->ino) ||
+	       !ctx->ipe_inode ||
+	       !ctx->ipe_inode->fs_verity_signed;
+}
+
+/**
+ * evaluate_fsv_sig_true - Analyze @ctx against a fsv sig true property.
+ * @ctx: Supplies a pointer to the context being evaluated.
+ *
+ * Return:
+ * * true - The current @ctx match the property
+ * * false - The current @ctx doesn't match the property
+ */
+static bool evaluate_fsv_sig_true(const struct ipe_eval_ctx *const ctx)
+{
+	return !evaluate_fsv_sig_false(ctx);
+}
+#else
+static bool evaluate_fsv_digest(const struct ipe_eval_ctx *const ctx,
+				struct ipe_prop *p)
+{
+	return false;
+}
+
+static bool evaluate_fsv_sig_false(const struct ipe_eval_ctx *const ctx)
+{
+	return false;
+}
+
+static bool evaluate_fsv_sig_true(const struct ipe_eval_ctx *const ctx)
+{
+	return false;
+}
+#endif /* CONFIG_IPE_PROP_FS_VERITY */
+
 /**
  * evaluate_property - Analyze @ctx against a property.
  * @ctx: Supplies a pointer to the context to be evaluated.
@@ -171,6 +271,12 @@  static bool evaluate_property(const struct ipe_eval_ctx *const ctx,
 		return evaluate_dmv_sig_false(ctx);
 	case IPE_PROP_DMV_SIG_TRUE:
 		return evaluate_dmv_sig_true(ctx);
+	case IPE_PROP_FSV_DIGEST:
+		return evaluate_fsv_digest(ctx, p);
+	case IPE_PROP_FSV_SIG_FALSE:
+		return evaluate_fsv_sig_false(ctx);
+	case IPE_PROP_FSV_SIG_TRUE:
+		return evaluate_fsv_sig_true(ctx);
 	default:
 		return false;
 	}
diff --git a/security/ipe/eval.h b/security/ipe/eval.h
index 494c0754f512..73ac905dc97d 100644
--- a/security/ipe/eval.h
+++ b/security/ipe/eval.h
@@ -29,6 +29,12 @@  struct ipe_bdev {
 };
 #endif /* CONFIG_IPE_PROP_DM_VERITY */
 
+#ifdef CONFIG_IPE_PROP_FS_VERITY
+struct ipe_inode {
+	bool fs_verity_signed;
+};
+#endif /* CONFIG_IPE_PROP_FS_VERITY */
+
 struct ipe_eval_ctx {
 	enum ipe_op_type op;
 	enum ipe_hook_type hook;
@@ -38,6 +44,10 @@  struct ipe_eval_ctx {
 #ifdef CONFIG_IPE_PROP_DM_VERITY
 	const struct ipe_bdev *ipe_bdev;
 #endif /* CONFIG_IPE_PROP_DM_VERITY */
+#ifdef CONFIG_IPE_PROP_FS_VERITY
+	const struct inode *ino;
+	const struct ipe_inode *ipe_inode;
+#endif /* CONFIG_IPE_PROP_FS_VERITY */
 };
 
 enum ipe_match {
diff --git a/security/ipe/hooks.c b/security/ipe/hooks.c
index f95986a87d51..30b60f1b2283 100644
--- a/security/ipe/hooks.c
+++ b/security/ipe/hooks.c
@@ -259,3 +259,31 @@  int ipe_bdev_setintegrity(struct block_device *bdev, enum lsm_integrity_type typ
 	return 0;
 }
 #endif /* CONFIG_IPE_PROP_DM_VERITY */
+
+#ifdef CONFIG_IPE_PROP_FS_VERITY
+/**
+ * ipe_inode_setintegrity - save integrity data from a inode to IPE's LSM blob.
+ * @inode: The inode to source the security blob from.
+ * @type: Supplies the integrity type.
+ * @value: The value to be stored.
+ * @size: The size of @value.
+ *
+ * Saves fsverity signature into inode security blob
+ *
+ * Return:
+ * * 0	- OK
+ * * !0	- Error
+ */
+int ipe_inode_setintegrity(struct inode *inode, enum lsm_integrity_type type,
+			   const void *value, size_t size)
+{
+	struct ipe_inode *inode_sec = ipe_inode(inode);
+
+	if (type == LSM_INT_FSVERITY_BUILTINSIG) {
+		inode_sec->fs_verity_signed = size > 0 && value;
+		return 0;
+	}
+
+	return 0;
+}
+#endif /* CONFIG_CONFIG_IPE_PROP_FS_VERITY */
diff --git a/security/ipe/hooks.h b/security/ipe/hooks.h
index 0d8f9a4896cc..06a28204407d 100644
--- a/security/ipe/hooks.h
+++ b/security/ipe/hooks.h
@@ -9,6 +9,7 @@ 
 #include <linux/binfmts.h>
 #include <linux/security.h>
 #include <linux/blk_types.h>
+#include <linux/fsverity.h>
 
 enum ipe_hook_type {
 	IPE_HOOK_BPRM_CHECK = 0,
@@ -43,4 +44,9 @@  int ipe_bdev_setintegrity(struct block_device *bdev, enum lsm_integrity_type typ
 			  const void *value, size_t len);
 #endif /* CONFIG_IPE_PROP_DM_VERITY */
 
+#ifdef CONFIG_IPE_PROP_FS_VERITY
+int ipe_inode_setintegrity(struct inode *inode, enum lsm_integrity_type type,
+			   const void *value, size_t size);
+#endif /* CONFIG_IPE_PROP_FS_VERITY */
+
 #endif /* _IPE_HOOKS_H */
diff --git a/security/ipe/ipe.c b/security/ipe/ipe.c
index 3d63e9672f12..86b87e287b69 100644
--- a/security/ipe/ipe.c
+++ b/security/ipe/ipe.c
@@ -16,6 +16,9 @@  static struct lsm_blob_sizes ipe_blobs __ro_after_init = {
 #ifdef CONFIG_IPE_PROP_DM_VERITY
 	.lbs_bdev = sizeof(struct ipe_bdev),
 #endif /* CONFIG_IPE_PROP_DM_VERITY */
+#ifdef CONFIG_IPE_PROP_FS_VERITY
+	.lbs_inode = sizeof(struct ipe_inode),
+#endif /* CONFIG_IPE_PROP_FS_VERITY */
 };
 
 static const struct lsm_id ipe_lsmid = {
@@ -35,6 +38,13 @@  struct ipe_bdev *ipe_bdev(struct block_device *b)
 }
 #endif /* CONFIG_IPE_PROP_DM_VERITY */
 
+#ifdef CONFIG_IPE_PROP_FS_VERITY
+struct ipe_inode *ipe_inode(const struct inode *inode)
+{
+	return inode->i_security + ipe_blobs.lbs_inode;
+}
+#endif /* CONFIG_IPE_PROP_FS_VERITY */
+
 static struct security_hook_list ipe_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(bprm_check_security, ipe_bprm_check_security),
 	LSM_HOOK_INIT(mmap_file, ipe_mmap_file),
@@ -46,6 +56,9 @@  static struct security_hook_list ipe_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(bdev_free_security, ipe_bdev_free_security),
 	LSM_HOOK_INIT(bdev_setintegrity, ipe_bdev_setintegrity),
 #endif /* CONFIG_IPE_PROP_DM_VERITY */
+#ifdef CONFIG_IPE_PROP_FS_VERITY
+	LSM_HOOK_INIT(inode_setintegrity, ipe_inode_setintegrity),
+#endif /* CONFIG_IPE_PROP_FS_VERITY */
 };
 
 /**
diff --git a/security/ipe/ipe.h b/security/ipe/ipe.h
index 64626702b689..57d3fc22fe10 100644
--- a/security/ipe/ipe.h
+++ b/security/ipe/ipe.h
@@ -19,5 +19,8 @@  extern bool ipe_enabled;
 #ifdef CONFIG_IPE_PROP_DM_VERITY
 struct ipe_bdev *ipe_bdev(struct block_device *b);
 #endif /* CONFIG_IPE_PROP_DM_VERITY */
+#ifdef CONFIG_IPE_PROP_FS_VERITY
+struct ipe_inode *ipe_inode(const struct inode *inode);
+#endif /* CONFIG_IPE_PROP_FS_VERITY */
 
 #endif /* _IPE_H */
diff --git a/security/ipe/policy.h b/security/ipe/policy.h
index 35629e9699f7..ae6264874fd3 100644
--- a/security/ipe/policy.h
+++ b/security/ipe/policy.h
@@ -36,6 +36,9 @@  enum ipe_prop_type {
 	IPE_PROP_DMV_ROOTHASH,
 	IPE_PROP_DMV_SIG_FALSE,
 	IPE_PROP_DMV_SIG_TRUE,
+	IPE_PROP_FSV_DIGEST,
+	IPE_PROP_FSV_SIG_FALSE,
+	IPE_PROP_FSV_SIG_TRUE,
 	__IPE_PROP_MAX
 };
 
diff --git a/security/ipe/policy_parser.c b/security/ipe/policy_parser.c
index 802e31f14b22..48dc11739072 100644
--- a/security/ipe/policy_parser.c
+++ b/security/ipe/policy_parser.c
@@ -273,6 +273,9 @@  static const match_table_t property_tokens = {
 	{IPE_PROP_DMV_ROOTHASH,		"dmverity_roothash=%s"},
 	{IPE_PROP_DMV_SIG_FALSE,	"dmverity_signature=FALSE"},
 	{IPE_PROP_DMV_SIG_TRUE,		"dmverity_signature=TRUE"},
+	{IPE_PROP_FSV_DIGEST,		"fsverity_digest=%s"},
+	{IPE_PROP_FSV_SIG_FALSE,	"fsverity_signature=FALSE"},
+	{IPE_PROP_FSV_SIG_TRUE,		"fsverity_signature=TRUE"},
 	{IPE_PROP_INVALID,		NULL}
 };
 
@@ -302,6 +305,7 @@  static int parse_property(char *t, struct ipe_rule *r)
 
 	switch (token) {
 	case IPE_PROP_DMV_ROOTHASH:
+	case IPE_PROP_FSV_DIGEST:
 		dup = match_strdup(&args[0]);
 		if (!dup) {
 			rc = -ENOMEM;
@@ -317,6 +321,8 @@  static int parse_property(char *t, struct ipe_rule *r)
 	case IPE_PROP_BOOT_VERIFIED_TRUE:
 	case IPE_PROP_DMV_SIG_FALSE:
 	case IPE_PROP_DMV_SIG_TRUE:
+	case IPE_PROP_FSV_SIG_FALSE:
+	case IPE_PROP_FSV_SIG_TRUE:
 		p->type = token;
 		break;
 	default: