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/* SPDX-License-Identifier: GPL-2.0 */
* fs-verity: read-only file-based authenticity protection
* Copyright 2019 Google LLC
#define DEBUG
#define pr_fmt(fmt) "fs-verity: " fmt
#include <crypto/sha.h>
#include <linux/fsverity.h>
#include <linux/mempool.h>
struct ahash_request;
* Implementation limit: maximum depth of the Merkle tree. For now 8 is plenty;
* it's enough for over U64_MAX bytes of data using SHA-256 and 4K blocks.
* Largest digest size among all hash algorithms supported by fs-verity.
* Currently assumed to be <= size of fsverity_descriptor::root_hash.
/* A hash algorithm supported by fs-verity */
struct fsverity_hash_alg {
struct crypto_ahash *tfm; /* hash tfm, allocated on demand */
const char *name; /* crypto API name, e.g. sha256 */
unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */
unsigned int block_size; /* block size in bytes, e.g. 64 for SHA-256 */
mempool_t req_pool; /* mempool with a preallocated hash request */
/* Merkle tree parameters: hash algorithm, initial hash state, and topology */
struct merkle_tree_params {
struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
const u8 *hashstate; /* initial hash state or NULL */
unsigned int digest_size; /* same as hash_alg->digest_size */
unsigned int block_size; /* size of data and tree blocks */
unsigned int hashes_per_block; /* number of hashes per tree block */
unsigned int log_blocksize; /* log2(block_size) */
unsigned int log_arity; /* log2(hashes_per_block) */
unsigned int num_levels; /* number of levels in Merkle tree */
u64 tree_size; /* Merkle tree size in bytes */
unsigned long level0_blocks; /* number of blocks in tree level 0 */
* Starting block index for each tree level, ordered from leaf level (0)
* to root level ('num_levels - 1')
u64 level_start[FS_VERITY_MAX_LEVELS];
* fsverity_info - cached verity metadata for an inode
* When a verity file is first opened, an instance of this struct is allocated
* and stored in ->i_verity_info; it remains until the inode is evicted. It
* caches information about the Merkle tree that's needed to efficiently verify
* data read from the file. It also caches the file measurement. The Merkle
* tree pages themselves are not cached here, but the filesystem may cache them.
struct fsverity_info {
struct merkle_tree_params tree_params;
u8 measurement[FS_VERITY_MAX_DIGEST_SIZE];
const struct inode *inode;
* Merkle tree properties. The file measurement is the hash of this structure
* excluding the signature and with the sig_size field set to 0.
struct fsverity_descriptor {
__u8 version; /* must be 1 */
__u8 hash_algorithm; /* Merkle tree hash algorithm */
__u8 log_blocksize; /* log2 of size of data and tree blocks */
__u8 salt_size; /* size of salt in bytes; 0 if none */
__le32 sig_size; /* size of signature in bytes; 0 if none */
__le64 data_size; /* size of file the Merkle tree is built over */
__u8 root_hash[64]; /* Merkle tree root hash */
__u8 salt[32]; /* salt prepended to each hashed block */
__u8 __reserved[144]; /* must be 0's */
__u8 signature[]; /* optional PKCS#7 signature */
/* Arbitrary limit to bound the kmalloc() size. Can be changed. */
sizeof(struct fsverity_descriptor))
* Format in which verity file measurements are signed. This is the same as
* 'struct fsverity_digest', except here some magic bytes are prepended to
* provide some context about what is being signed in case the same key is used
* for non-fsverity purposes, and here the fields have fixed endianness.
struct fsverity_signed_digest {
char magic[8]; /* must be "FSVerity" */
__le16 digest_algorithm;
__le16 digest_size;
__u8 digest[];
/* hash_algs.c */
extern struct fsverity_hash_alg fsverity_hash_algs[];
struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
unsigned int num);
struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,
gfp_t gfp_flags);
void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
struct ahash_request *req);
const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
const u8 *salt, size_t salt_size);
int fsverity_hash_page(const struct merkle_tree_params *params,
const struct inode *inode,
struct ahash_request *req, struct page *page, u8 *out);
int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
const void *data, size_t size, u8 *out);
void __init fsverity_check_hash_algs(void);
/* init.c */
void __printf(3, 4) __cold
fsverity_msg(const struct inode *inode, const char *level,
const char *fmt, ...);
#define fsverity_warn(inode, fmt, ...) \
fsverity_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
#define fsverity_err(inode, fmt, ...) \
fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
/* open.c */
int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
const struct inode *inode,
unsigned int hash_algorithm,
unsigned int log_blocksize,
const u8 *salt, size_t salt_size);
struct fsverity_info *fsverity_create_info(const struct inode *inode,
void *desc, size_t desc_size);
void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
void fsverity_free_info(struct fsverity_info *vi);
int __init fsverity_init_info_cache(void);
void __init fsverity_exit_info_cache(void);
/* signature.c */
int fsverity_verify_signature(const struct fsverity_info *vi,
const struct fsverity_descriptor *desc,
size_t desc_size);
int __init fsverity_init_signature(void);
static inline int
fsverity_verify_signature(const struct fsverity_info *vi,
const struct fsverity_descriptor *desc,
size_t desc_size)
return 0;
static inline int fsverity_init_signature(void)
return 0;
/* verify.c */
int __init fsverity_init_workqueue(void);
void __init fsverity_exit_workqueue(void);
#endif /* _FSVERITY_PRIVATE_H */