ipe: introduce 'boot_verified' as a trust provider

IPE is designed to provide system level trust guarantees, this usually
implies that trust starts from bootup with a hardware root of trust,
which validates the bootloader. After this, the bootloader verifies
the kernel and the initramfs.

As there's no currently supported integrity method for initramfs, and
it's typically already verified by the bootloader. This patch introduces
a new IPE property `boot_verified` which allows author of IPE policy to
indicate trust for files from initramfs.

The implementation of this feature utilizes the newly added
`initramfs_populated` hook. This hook marks the superblock of the rootfs
after the initramfs has been unpacked into it.

Before mounting the real rootfs on top of the initramfs, initramfs
script will recursively remove all files and directories on the
initramfs. This is typically implemented by using switch_root(8)
(https://man7.org/linux/man-pages/man8/switch_root.8.html).
Therefore the initramfs will be empty and not accessible after the real
rootfs takes over. It is advised to switch to a different policy
that doesn't rely on the `boot_verified` property after this point.
This ensures that the trust policies remain relevant and effective
throughout the system's operation.

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

security/ipe/eval.c

@@ -16,6 +16,18 @@
 
 struct ipe_policy __rcu *ipe_active_policy;
 
+#define FILE_SUPERBLOCK(f) ((f)->f_path.mnt->mnt_sb)
+
+/**
+ * build_ipe_sb_ctx() - Build initramfs field of an ipe evaluation context.
+ * @ctx: Supplies a pointer to the context to be populated.
+ * @file: Supplies the file struct of the file triggered IPE event.
+ */
+static void build_ipe_sb_ctx(struct ipe_eval_ctx *ctx, const struct file *const file)
+{
+	ctx->initramfs = ipe_sb(FILE_SUPERBLOCK(file))->initramfs;
+}
+
 /**
  * ipe_build_eval_ctx() - Build an ipe evaluation context.
  * @ctx: Supplies a pointer to the context to be populated.
@@ -28,6 +40,22 @@ void ipe_build_eval_ctx(struct ipe_eval_ctx *ctx,
 {
 	ctx->file = file;
 	ctx->op = op;
+
+	if (file)
+		build_ipe_sb_ctx(ctx, file);
+}
+
+/**
+ * evaluate_boot_verified() - Evaluate @ctx for the boot verified property.
+ * @ctx: Supplies a pointer to the context being evaluated.
+ *
+ * Return:
+ * * %true	- The current @ctx match the @p
+ * * %false	- The current @ctx doesn't match the @p
+ */
+static bool evaluate_boot_verified(const struct ipe_eval_ctx *const ctx)
+{
+	return ctx->initramfs;
 }
 
 /**
@@ -35,8 +63,8 @@ void ipe_build_eval_ctx(struct ipe_eval_ctx *ctx,
  * @ctx: Supplies a pointer to the context to be evaluated.
  * @p: Supplies a pointer to the property to be evaluated.
  *
- * This is a placeholder. The actual function will be introduced in the
- * latter commits.
+ * This function Determines whether the specified @ctx
+ * matches the conditions defined by a rule property @p.
  *
  * Return:
  * * %true	- The current @ctx match the @p
@@ -45,7 +73,14 @@ void ipe_build_eval_ctx(struct ipe_eval_ctx *ctx,
 static bool evaluate_property(const struct ipe_eval_ctx *const ctx,
 			      struct ipe_prop *p)
 {
+	switch (p->type) {
+	case IPE_PROP_BOOT_VERIFIED_FALSE:
+		return !evaluate_boot_verified(ctx);
+	case IPE_PROP_BOOT_VERIFIED_TRUE:
+		return evaluate_boot_verified(ctx);
+	default:
 		return false;
+	}
 }
 
 /**

security/ipe/eval.h

@@ -15,10 +15,15 @@
 
 extern struct ipe_policy __rcu *ipe_active_policy;
 
+struct ipe_superblock {
+	bool initramfs;
+};
+
 struct ipe_eval_ctx {
 	enum ipe_op_type op;
 
 	const struct file *file;
+	bool initramfs;
 };
 
 void ipe_build_eval_ctx(struct ipe_eval_ctx *ctx,

security/ipe/hooks.c

@@ -4,6 +4,7 @@
  */
 
 #include <linux/fs.h>
+#include <linux/fs_struct.h>
 #include <linux/types.h>
 #include <linux/binfmts.h>
 #include <linux/mman.h>
@@ -182,3 +183,11 @@ int ipe_kernel_load_data(enum kernel_load_data_id id, bool contents)
 	ipe_build_eval_ctx(&ctx, NULL, op);
 	return ipe_evaluate_event(&ctx);
 }
+
+/**
+ * ipe_unpack_initramfs() - Mark the current rootfs as initramfs.
+ */
+void ipe_unpack_initramfs(void)
+{
+	ipe_sb(current->fs->root.mnt->mnt_sb)->initramfs = true;
+}

security/ipe/hooks.h

@@ -22,4 +22,6 @@ int ipe_kernel_read_file(struct file *file, enum kernel_read_file_id id,
 
 int ipe_kernel_load_data(enum kernel_load_data_id id, bool contents);
 
+void ipe_unpack_initramfs(void);
+
 #endif /* _IPE_HOOKS_H */

security/ipe/ipe.c

@@ -5,9 +5,11 @@
 #include <uapi/linux/lsm.h>
 
 #include "ipe.h"
+#include "eval.h"
 #include "hooks.h"
 
 static struct lsm_blob_sizes ipe_blobs __ro_after_init = {
+	.lbs_superblock = sizeof(struct ipe_superblock),
 };
 
 static const struct lsm_id ipe_lsmid = {
@@ -15,12 +17,18 @@ static const struct lsm_id ipe_lsmid = {
 	.id = LSM_ID_IPE,
 };
 
+struct ipe_superblock *ipe_sb(const struct super_block *sb)
+{
+	return sb->s_security + ipe_blobs.lbs_superblock;
+}
+
 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),
 	LSM_HOOK_INIT(file_mprotect, ipe_file_mprotect),
 	LSM_HOOK_INIT(kernel_read_file, ipe_kernel_read_file),
 	LSM_HOOK_INIT(kernel_load_data, ipe_kernel_load_data),
+	LSM_HOOK_INIT(initramfs_populated, ipe_unpack_initramfs),
 };
 
 /**

security/ipe/ipe.h

@@ -12,5 +12,6 @@
 #define pr_fmt(fmt) "ipe: " fmt
 
 #include <linux/lsm_hooks.h>
+struct ipe_superblock *ipe_sb(const struct super_block *sb);
 
 #endif /* _IPE_H */

security/ipe/policy.h

@@ -30,6 +30,8 @@ enum ipe_action_type {
 #define IPE_ACTION_INVALID __IPE_ACTION_MAX
 
 enum ipe_prop_type {
+	IPE_PROP_BOOT_VERIFIED_FALSE,
+	IPE_PROP_BOOT_VERIFIED_TRUE,
 	__IPE_PROP_MAX
 };
 

security/ipe/policy_parser.c

@@ -270,13 +270,19 @@ static enum ipe_action_type parse_action(char *t)
 	return match_token(t, action_tokens, args);
 }
 
+static const match_table_t property_tokens = {
+	{IPE_PROP_BOOT_VERIFIED_FALSE,	"boot_verified=FALSE"},
+	{IPE_PROP_BOOT_VERIFIED_TRUE,	"boot_verified=TRUE"},
+	{IPE_PROP_INVALID,		NULL}
+};
+
 /**
  * parse_property() - Parse a rule property given a token string.
  * @t: Supplies the token string to be parsed.
  * @r: Supplies the ipe_rule the parsed property will be associated with.
  *
- * This is a placeholder. The actual function will be introduced in the
- * latter commits.
+ * This function parses and associates a property with an IPE rule based
+ * on a token string.
  *
  * Return:
  * * %0		- Success
@@ -285,7 +291,34 @@ static enum ipe_action_type parse_action(char *t)
  */
 static int parse_property(char *t, struct ipe_rule *r)
 {
-	return -EBADMSG;
+	substring_t args[MAX_OPT_ARGS];
+	struct ipe_prop *p = NULL;
+	int rc = 0;
+	int token;
+
+	p = kzalloc(sizeof(*p), GFP_KERNEL);
+	if (!p)
+		return -ENOMEM;
+
+	token = match_token(t, property_tokens, args);
+
+	switch (token) {
+	case IPE_PROP_BOOT_VERIFIED_FALSE:
+	case IPE_PROP_BOOT_VERIFIED_TRUE:
+		p->type = token;
+		break;
+	default:
+		rc = -EBADMSG;
+		break;
+	}
+	if (rc)
+		goto err;
+	list_add_tail(&p->next, &r->props);
+
+	return rc;
+err:
+	kfree(p);
+	return rc;
 }
 
 /**