[v3,02/13] security: Introduce the digest_cache LSM

diff --git a/MAINTAINERS b/MAINTAINERS
index d3d13fb1004b..3e3236dd0b26 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6155,6 +6155,12 @@  L:	linux-gpio@vger.kernel.org
 S:	Maintained
 F:	drivers/gpio/gpio-gpio-mm.c
 
+DIGEST_CACHE LSM
+M:	Roberto Sassu <roberto.sassu@huawei.com>
+L:	linux-security-module@vger.kernel.org
+S:	Maintained
+F:	security/digest_cache/
+
 DIGITEQ AUTOMOTIVE MGB4 V4L2 DRIVER
 M:	Martin Tuma <martin.tuma@digiteqautomotive.com>
 L:	linux-media@vger.kernel.org
diff --git a/include/linux/digest_cache.h b/include/linux/digest_cache.h
new file mode 100644
index 000000000000..e79f94a60b0f
--- /dev/null
+++ b/include/linux/digest_cache.h
@@ -0,0 +1,32 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@huawei.com>
+ *
+ * Public API of the digest_cache LSM.
+ */
+
+#ifndef _LINUX_DIGEST_CACHE_H
+#define _LINUX_DIGEST_CACHE_H
+
+#include <linux/fs.h>
+
+struct digest_cache;
+
+#ifdef CONFIG_SECURITY_DIGEST_CACHE
+struct digest_cache *digest_cache_get(struct dentry *dentry);
+void digest_cache_put(struct digest_cache *digest_cache);
+
+#else
+static inline struct digest_cache *digest_cache_get(struct dentry *dentry)
+{
+	return NULL;
+}
+
+static inline void digest_cache_put(struct digest_cache *digest_cache)
+{
+}
+
+#endif /* CONFIG_SECURITY_DIGEST_CACHE */
+#endif /* _LINUX_DIGEST_CACHE_H */
diff --git a/include/uapi/linux/lsm.h b/include/uapi/linux/lsm.h
index f8aef9ade549..205d969f20ff 100644
--- a/include/uapi/linux/lsm.h
+++ b/include/uapi/linux/lsm.h
@@ -62,6 +62,7 @@  struct lsm_ctx {
 #define LSM_ID_LOCKDOWN		108
 #define LSM_ID_BPF		109
 #define LSM_ID_LANDLOCK		110
+#define LSM_ID_DIGEST_CACHE	111
 
 /*
  * LSM_ATTR_XXX definitions identify different LSM attributes
diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h
index 9463db2dfa9d..8a58cf4bce65 100644
--- a/include/uapi/linux/xattr.h
+++ b/include/uapi/linux/xattr.h
@@ -54,6 +54,9 @@ 
 #define XATTR_IMA_SUFFIX "ima"
 #define XATTR_NAME_IMA XATTR_SECURITY_PREFIX XATTR_IMA_SUFFIX
 
+#define XATTR_DIGEST_LIST_SUFFIX "digest_list"
+#define XATTR_NAME_DIGEST_LIST XATTR_SECURITY_PREFIX XATTR_DIGEST_LIST_SUFFIX
+
 #define XATTR_SELINUX_SUFFIX "selinux"
 #define XATTR_NAME_SELINUX XATTR_SECURITY_PREFIX XATTR_SELINUX_SUFFIX
 
diff --git a/security/Kconfig b/security/Kconfig
index 52c9af08ad35..99f99cbd94cc 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -194,6 +194,7 @@  source "security/yama/Kconfig"
 source "security/safesetid/Kconfig"
 source "security/lockdown/Kconfig"
 source "security/landlock/Kconfig"
+source "security/digest_cache/Kconfig"
 
 source "security/integrity/Kconfig"
 
@@ -233,11 +234,11 @@  endchoice
 
 config LSM
 	string "Ordered list of enabled LSMs"
-	default "landlock,lockdown,yama,loadpin,safesetid,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK
-	default "landlock,lockdown,yama,loadpin,safesetid,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR
-	default "landlock,lockdown,yama,loadpin,safesetid,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO
-	default "landlock,lockdown,yama,loadpin,safesetid,bpf" if DEFAULT_SECURITY_DAC
-	default "landlock,lockdown,yama,loadpin,safesetid,selinux,smack,tomoyo,apparmor,bpf"
+	default "digest_cache,landlock,lockdown,yama,loadpin,safesetid,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK
+	default "digest_cache,landlock,lockdown,yama,loadpin,safesetid,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR
+	default "digest_cache,landlock,lockdown,yama,loadpin,safesetid,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO
+	default "digest_cache,landlock,lockdown,yama,loadpin,safesetid,bpf" if DEFAULT_SECURITY_DAC
+	default "digest_cache,landlock,lockdown,yama,loadpin,safesetid,selinux,smack,tomoyo,apparmor,bpf"
 	help
 	  A comma-separated list of LSMs, in initialization order.
 	  Any LSMs left off this list, except for those with order
diff --git a/security/Makefile b/security/Makefile
index 59f238490665..e9b43e7b715a 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -25,6 +25,7 @@  obj-$(CONFIG_SECURITY_LOCKDOWN_LSM)	+= lockdown/
 obj-$(CONFIG_CGROUPS)			+= device_cgroup.o
 obj-$(CONFIG_BPF_LSM)			+= bpf/
 obj-$(CONFIG_SECURITY_LANDLOCK)		+= landlock/
+obj-$(CONFIG_SECURITY_DIGEST_CACHE)	+= digest_cache/
 
 # Object integrity file lists
 obj-$(CONFIG_INTEGRITY)			+= integrity/
diff --git a/security/digest_cache/Kconfig b/security/digest_cache/Kconfig
new file mode 100644
index 000000000000..0c47d5151f07
--- /dev/null
+++ b/security/digest_cache/Kconfig
@@ -0,0 +1,17 @@ 
+# SPDX-License-Identifier: GPL-2.0
+config SECURITY_DIGEST_CACHE
+	bool "Digest_cache LSM"
+	default n
+	help
+	   This option enables an LSM maintaining a cache of digests
+	   (e.g. of file content or metadata).
+
+	   This LSM can support other kernel components in making access
+	   control decisions.
+
+config DIGEST_LIST_DEFAULT_PATH
+	string
+	default "/etc/digest_lists"
+	help
+	   Default directory where digest_cache LSM expects to find digest
+	   lists.
diff --git a/security/digest_cache/Makefile b/security/digest_cache/Makefile
new file mode 100644
index 000000000000..48848c41253e
--- /dev/null
+++ b/security/digest_cache/Makefile
@@ -0,0 +1,7 @@ 
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for building the digest_cache LSM.
+
+obj-$(CONFIG_SECURITY_DIGEST_CACHE) += digest_cache.o
+
+digest_cache-y := main.o
diff --git a/security/digest_cache/internal.h b/security/digest_cache/internal.h
new file mode 100644
index 000000000000..5f04844af3a5
--- /dev/null
+++ b/security/digest_cache/internal.h
@@ -0,0 +1,86 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@huawei.com>
+ *
+ * Internal header of the digest_cache LSM.
+ */
+
+#ifndef _DIGEST_CACHE_INTERNAL_H
+#define _DIGEST_CACHE_INTERNAL_H
+
+#include <linux/lsm_hooks.h>
+#include <linux/digest_cache.h>
+
+/* Digest cache bits in flags. */
+#define INIT_IN_PROGRESS	0	/* Digest cache being initialized. */
+
+/**
+ * struct digest_cache - Digest cache
+ * @ref_count: Number of references to the digest cache
+ * @path_str: Path of the digest list the digest cache was created from
+ * @flags: Control flags
+ *
+ * This structure represents a cache of digests extracted from a digest list.
+ */
+struct digest_cache {
+	atomic_t ref_count;
+	char *path_str;
+	unsigned long flags;
+};
+
+/**
+ * struct digest_cache_security - Digest cache pointers in inode security blob
+ * @dig_owner: Digest cache created from this inode
+ * @dig_owner_mutex: Protects @dig_owner
+ * @dig_user: Digest cache requested for this inode
+ * @dig_user_mutex: Protects @dig_user
+ *
+ * This structure contains references to digest caches, protected by their
+ * respective mutex.
+ */
+struct digest_cache_security {
+	struct digest_cache *dig_owner;
+	struct mutex dig_owner_mutex;
+	struct digest_cache *dig_user;
+	struct mutex dig_user_mutex;
+};
+
+extern struct lsm_blob_sizes digest_cache_blob_sizes;
+extern char *default_path_str;
+
+static inline struct digest_cache_security *
+digest_cache_get_security(const struct inode *inode)
+{
+	if (unlikely(!inode->i_security))
+		return NULL;
+
+	return inode->i_security + digest_cache_blob_sizes.lbs_inode;
+}
+
+static inline struct digest_cache *
+digest_cache_ref(struct digest_cache *digest_cache)
+{
+	atomic_inc(&digest_cache->ref_count);
+	pr_debug("Ref (+) digest cache %s (ref count: %d)\n",
+		 digest_cache->path_str, atomic_read(&digest_cache->ref_count));
+	return digest_cache;
+}
+
+static inline struct digest_cache *
+digest_cache_unref(struct digest_cache *digest_cache)
+{
+	bool ref_is_zero = atomic_dec_and_test(&digest_cache->ref_count);
+
+	pr_debug("Ref (-) digest cache %s (ref count: %d)\n",
+		 digest_cache->path_str, atomic_read(&digest_cache->ref_count));
+	return (ref_is_zero) ? digest_cache : NULL;
+}
+
+/* main.c */
+struct digest_cache *digest_cache_create(struct dentry *dentry,
+					 struct path *digest_list_path,
+					 char *path_str, char *filename);
+
+#endif /* _DIGEST_CACHE_INTERNAL_H */
diff --git a/security/digest_cache/main.c b/security/digest_cache/main.c
new file mode 100644
index 000000000000..166798e6247e
--- /dev/null
+++ b/security/digest_cache/main.c
@@ -0,0 +1,397 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@huawei.com>
+ *
+ * Implement the main code of the digest_cache LSM.
+ */
+
+#define pr_fmt(fmt) "DIGEST CACHE: "fmt
+#include <linux/namei.h>
+#include <linux/xattr.h>
+
+#include "internal.h"
+
+static int digest_cache_enabled __ro_after_init = 1;
+static struct kmem_cache *digest_cache_cache __read_mostly;
+
+char *default_path_str = CONFIG_DIGEST_LIST_DEFAULT_PATH;
+
+/**
+ * digest_cache_alloc_init - Allocate and initialize a new digest cache
+ * @path_str: Path string of the digest list
+ * @filename: Digest list file name (can be an empty string)
+ *
+ * This function allocates and initializes a new digest cache.
+ *
+ * Return: A digest_cache structure on success, NULL on error.
+ */
+static struct digest_cache *digest_cache_alloc_init(char *path_str,
+						    char *filename)
+{
+	struct digest_cache *digest_cache;
+
+	digest_cache = kmem_cache_alloc(digest_cache_cache, GFP_KERNEL);
+	if (!digest_cache)
+		return digest_cache;
+
+	digest_cache->path_str = kasprintf(GFP_KERNEL, "%s%s%s", path_str,
+					   filename[0] ? "/" : "", filename);
+	if (!digest_cache->path_str) {
+		kmem_cache_free(digest_cache_cache, digest_cache);
+		return NULL;
+	}
+
+	atomic_set(&digest_cache->ref_count, 1);
+	digest_cache->flags = 0UL;
+
+	pr_debug("New digest cache %s (ref count: %d)\n",
+		 digest_cache->path_str, atomic_read(&digest_cache->ref_count));
+
+	return digest_cache;
+}
+
+/**
+ * digest_cache_free - Free all memory occupied by the digest cache
+ * @digest_cache: Digest cache
+ *
+ * This function frees the memory occupied by the digest cache.
+ */
+static void digest_cache_free(struct digest_cache *digest_cache)
+{
+	pr_debug("Freed digest cache %s\n", digest_cache->path_str);
+	kfree(digest_cache->path_str);
+	kmem_cache_free(digest_cache_cache, digest_cache);
+}
+
+/**
+ * digest_cache_create - Create a digest cache
+ * @dentry: Dentry of the inode for which the digest cache will be used
+ * @digest_list_path: Path structure of the digest list
+ * @path_str: Path string of the digest list
+ * @filename: Digest list file name (can be an empty string)
+ *
+ * This function first locates, from the passed path, the digest list inode
+ * from which the digest cache will be created or retrieved (if it already
+ * exists).
+ *
+ * If dig_owner is NULL in the inode security blob, this function creates a
+ * new digest cache with reference count set to 1 (reference returned), sets
+ * it to dig_owner and consequently increments again the digest cache reference
+ * count.
+ *
+ * Otherwise, it simply increments the reference count of the existing
+ * dig_owner, since that reference is returned to the caller.
+ *
+ * Incrementing the reference count twice before calling path_put() ensures
+ * that the digest cache returned is valid even if the inode is evicted from
+ * memory (which decreases the reference count).
+ *
+ * Releasing the dig_owner_mutex lock does not mean that the digest cache is
+ * ready for use. digest_cache_create() callers that found a partially
+ * instantiated digest cache have to wait until the INIT_IN_PROGRESS bit is
+ * cleared by the caller that is actually creating that digest cache.
+ *
+ * Return: A new digest cache on success, NULL on error.
+ */
+struct digest_cache *digest_cache_create(struct dentry *dentry,
+					 struct path *digest_list_path,
+					 char *path_str, char *filename)
+{
+	struct path file_path;
+	struct digest_cache *digest_cache = NULL;
+	struct digest_cache_security *dig_sec;
+	struct inode *inode = d_backing_inode(digest_list_path->dentry);
+	bool dig_owner_exists = false;
+	int ret;
+
+	if (S_ISDIR(d_backing_inode(digest_list_path->dentry)->i_mode) &&
+	    filename[0]) {
+		ret = vfs_path_lookup(digest_list_path->dentry,
+				      digest_list_path->mnt, filename, 0,
+				      &file_path);
+		if (ret < 0) {
+			pr_debug("Cannot find digest list %s/%s\n", path_str,
+				 filename);
+			return NULL;
+		}
+
+		digest_list_path = &file_path;
+		inode = d_backing_inode(file_path.dentry);
+
+		/*
+		 * Cannot request a digest cache for the same inode the
+		 * digest cache is populated from.
+		 */
+		if (d_backing_inode(dentry) == inode)
+			return NULL;
+
+		/* No support for nested directories. */
+		if (!S_ISREG(inode->i_mode))
+			return NULL;
+	}
+
+	dig_sec = digest_cache_get_security(inode);
+	if (unlikely(!dig_sec))
+		goto out;
+
+	/* Serialize check and assignment of dig_owner. */
+	mutex_lock(&dig_sec->dig_owner_mutex);
+	if (dig_sec->dig_owner) {
+		/* Increment ref. count for reference returned to the caller. */
+		digest_cache = digest_cache_ref(dig_sec->dig_owner);
+		dig_owner_exists = true;
+		mutex_unlock(&dig_sec->dig_owner_mutex);
+		goto exists;
+	}
+
+	/* Ref. count is already 1 for this reference. */
+	digest_cache = digest_cache_alloc_init(path_str, filename);
+	if (!digest_cache) {
+		mutex_unlock(&dig_sec->dig_owner_mutex);
+		goto out;
+	}
+
+	/* Increment ref. count for reference set to dig_owner. */
+	dig_sec->dig_owner = digest_cache_ref(digest_cache);
+
+	/* Make the other lock contenders wait until creation complete. */
+	set_bit(INIT_IN_PROGRESS, &dig_sec->dig_owner->flags);
+	mutex_unlock(&dig_sec->dig_owner_mutex);
+
+	/* Creation complete, notify the other lock contenders. */
+	clear_and_wake_up_bit(INIT_IN_PROGRESS, &dig_sec->dig_owner->flags);
+exists:
+	if (dig_owner_exists)
+		/* Wait until creation complete. */
+		wait_on_bit(&dig_sec->dig_owner->flags, INIT_IN_PROGRESS,
+			    TASK_UNINTERRUPTIBLE);
+out:
+	if (digest_list_path == &file_path)
+		path_put(&file_path);
+
+	return digest_cache;
+}
+
+/**
+ * digest_cache_new - Retrieve digest list file name and request digest cache
+ * @dentry: Dentry of the inode for which the digest cache will be used
+ *
+ * This function locates the default path. If it is a file, it directly creates
+ * a digest cache from it. Otherwise, it reads the digest list file name from
+ * the security.digest_list xattr and requests the creation of a digest cache
+ * with that file name. If security.digest_list is not found, this function
+ * requests the creation of a digest cache on the parent directory.
+ *
+ * Return: A new digest cache on success, NULL on error.
+ */
+static struct digest_cache *digest_cache_new(struct dentry *dentry)
+{
+	char filename[NAME_MAX + 1] = { 0 };
+	struct digest_cache *digest_cache = NULL;
+	struct path default_path;
+	int ret;
+
+	ret = kern_path(default_path_str, 0, &default_path);
+	if (ret < 0) {
+		pr_debug("Cannot find path %s\n", default_path_str);
+		return NULL;
+	}
+
+	/* The default path is a file, no need to get xattr. */
+	if (S_ISREG(d_backing_inode(default_path.dentry)->i_mode)) {
+		pr_debug("Default path %s is a file, not reading %s xattr\n",
+			 default_path_str, XATTR_NAME_DIGEST_LIST);
+		goto create;
+	} else if (!S_ISDIR(d_backing_inode(default_path.dentry)->i_mode)) {
+		pr_debug("Default path %s must be either a file or a directory\n",
+			 default_path_str);
+		goto out;
+	}
+
+	ret = vfs_getxattr(&nop_mnt_idmap, dentry, XATTR_NAME_DIGEST_LIST,
+			   filename, sizeof(filename) - 1);
+	if (ret <= 0) {
+		pr_debug("Digest list path not found for file %s, using %s\n",
+			 dentry->d_name.name, default_path_str);
+		goto create;
+	}
+
+	if (strchr(filename, '/')) {
+		pr_debug("%s xattr should contain only a file name, got: %s\n",
+			 XATTR_NAME_DIGEST_LIST, filename);
+		goto out;
+	}
+
+	pr_debug("Found %s xattr in %s, default path: %s, digest list: %s\n",
+		 XATTR_NAME_DIGEST_LIST, dentry->d_name.name, default_path_str,
+		 filename);
+create:
+	digest_cache = digest_cache_create(dentry, &default_path,
+					   default_path_str, filename);
+out:
+	path_put(&default_path);
+	return digest_cache;
+}
+
+/**
+ * digest_cache_get - Get a digest cache for a given inode
+ * @dentry: Dentry of the inode for which the digest cache will be used
+ *
+ * This function tries to find a digest cache from the inode security blob of
+ * the passed dentry (dig_user field). If a digest cache was not found, it calls
+ * digest_cache_new() to create a new one. In both cases, it increments the
+ * digest cache reference count before returning the reference to the caller.
+ *
+ * The caller is responsible to call digest_cache_put() to release the digest
+ * cache reference returned.
+ *
+ * Lock dig_user_mutex to protect against concurrent requests to obtain a digest
+ * cache for the same inode, and to make other contenders wait until the first
+ * requester finishes the process.
+ *
+ * Return: A digest cache on success, NULL otherwise.
+ */
+struct digest_cache *digest_cache_get(struct dentry *dentry)
+{
+	struct digest_cache_security *dig_sec;
+	struct digest_cache *digest_cache = NULL;
+
+	if (!digest_cache_enabled)
+		return NULL;
+
+	dig_sec = digest_cache_get_security(d_backing_inode(dentry));
+	if (unlikely(!dig_sec))
+		return NULL;
+
+	/* Serialize accesses to inode for which the digest cache is used. */
+	mutex_lock(&dig_sec->dig_user_mutex);
+	if (!dig_sec->dig_user)
+		/* Consume extra reference from digest_cache_create(). */
+		dig_sec->dig_user = digest_cache_new(dentry);
+
+	if (dig_sec->dig_user)
+		/* Increment ref. count for reference returned to the caller. */
+		digest_cache = digest_cache_ref(dig_sec->dig_user);
+
+	mutex_unlock(&dig_sec->dig_user_mutex);
+	return digest_cache;
+}
+EXPORT_SYMBOL_GPL(digest_cache_get);
+
+/**
+ * digest_cache_put - Release a digest cache reference
+ * @digest_cache: Digest cache
+ *
+ * This function decrements the reference count of the digest cache passed as
+ * argument. If the reference count reaches zero, it calls digest_cache_free()
+ * to free the digest cache.
+ */
+void digest_cache_put(struct digest_cache *digest_cache)
+{
+	struct digest_cache *to_free;
+
+	to_free = digest_cache_unref(digest_cache);
+	if (!to_free)
+		return;
+
+	digest_cache_free(to_free);
+}
+EXPORT_SYMBOL_GPL(digest_cache_put);
+
+struct lsm_blob_sizes digest_cache_blob_sizes __ro_after_init = {
+	.lbs_inode = sizeof(struct digest_cache_security),
+};
+
+/**
+ * digest_cache_inode_alloc_security - Initialize inode security blob
+ * @inode: Inode for which the security blob is initialized
+ *
+ * This function initializes the digest_cache_security structure, directly
+ * stored in the inode security blob.
+ *
+ * Return: Zero.
+ */
+static int digest_cache_inode_alloc_security(struct inode *inode)
+{
+	struct digest_cache_security *dig_sec;
+
+	/* The inode security blob is always allocated here. */
+	dig_sec = digest_cache_get_security(inode);
+	mutex_init(&dig_sec->dig_owner_mutex);
+	mutex_init(&dig_sec->dig_user_mutex);
+	return 0;
+}
+
+/**
+ * digest_cache_inode_free_security - Release the digest cache references
+ * @inode: Inode for which the digest cache references are released
+ *
+ * Since the inode is being evicted, this function releases the non-needed
+ * references to the digest_caches stored in the digest_cache_security
+ * structure.
+ */
+static void digest_cache_inode_free_security(struct inode *inode)
+{
+	struct digest_cache_security *dig_sec;
+
+	dig_sec = digest_cache_get_security(inode);
+	if (!dig_sec)
+		return;
+
+	mutex_destroy(&dig_sec->dig_owner_mutex);
+	mutex_destroy(&dig_sec->dig_user_mutex);
+	if (dig_sec->dig_owner)
+		digest_cache_put(dig_sec->dig_owner);
+	if (dig_sec->dig_user)
+		digest_cache_put(dig_sec->dig_user);
+}
+
+static struct security_hook_list digest_cache_hooks[] __ro_after_init = {
+	LSM_HOOK_INIT(inode_alloc_security, digest_cache_inode_alloc_security),
+	LSM_HOOK_INIT(inode_free_security, digest_cache_inode_free_security),
+};
+
+/**
+ * digest_cache_init_once - Initialize the digest cache structure
+ * @foo: Digest cache structure to initialize
+ *
+ * This function fills the digest cache structure with zeros.
+ */
+static void digest_cache_init_once(void *foo)
+{
+	struct digest_cache *digest_cache = (struct digest_cache *)foo;
+
+	memset(digest_cache, 0, sizeof(*digest_cache));
+}
+
+static const struct lsm_id digest_cache_lsmid = {
+	.name = "digest_cache",
+	.id = LSM_ID_DIGEST_CACHE,
+};
+
+/**
+ * digest_cache_init - Initialize the digest_cache LSM
+ *
+ * Initialize the digest_cache LSM, by instantiating a cache for the
+ * digest_cache structure and by registering the digest_cache LSM hooks.
+ */
+static int __init digest_cache_init(void)
+{
+	digest_cache_cache = kmem_cache_create("digest_cache_cache",
+					       sizeof(struct digest_cache),
+					       0, SLAB_PANIC,
+					       digest_cache_init_once);
+
+	security_add_hooks(digest_cache_hooks, ARRAY_SIZE(digest_cache_hooks),
+			   &digest_cache_lsmid);
+	return 0;
+}
+
+DEFINE_LSM(digest_cache) = {
+	.name = "digest_cache",
+	.enabled = &digest_cache_enabled,
+	.init = digest_cache_init,
+	.blobs = &digest_cache_blob_sizes,
+};
diff --git a/security/security.c b/security/security.c
index da827d7cbad8..570f52d534f8 100644
--- a/security/security.c
+++ b/security/security.c
@@ -50,7 +50,8 @@ 
 	(IS_ENABLED(CONFIG_SECURITY_SAFESETID) ? 1 : 0) + \
 	(IS_ENABLED(CONFIG_SECURITY_LOCKDOWN_LSM) ? 1 : 0) + \
 	(IS_ENABLED(CONFIG_BPF_LSM) ? 1 : 0) + \
-	(IS_ENABLED(CONFIG_SECURITY_LANDLOCK) ? 1 : 0))
+	(IS_ENABLED(CONFIG_SECURITY_LANDLOCK) ? 1 : 0) + \
+	(IS_ENABLED(CONFIG_SECURITY_DIGEST_CACHE) ? 1 : 0))
 
 /*
  * These are descriptions of the reasons that can be passed to the
diff --git a/tools/testing/selftests/lsm/lsm_list_modules_test.c b/tools/testing/selftests/lsm/lsm_list_modules_test.c
index 9df29b1e3497..24fb9c038434 100644
--- a/tools/testing/selftests/lsm/lsm_list_modules_test.c
+++ b/tools/testing/selftests/lsm/lsm_list_modules_test.c
@@ -122,6 +122,9 @@  TEST(correct_lsm_list_modules)
 		case LSM_ID_LANDLOCK:
 			name = "landlock";
 			break;
+		case LSM_ID_DIGEST_CACHE:
+			name = "digest_cache";
+			break;
 		default:
 			name = "INVALID";
 			break;