193 lines
6.4 KiB
C
193 lines
6.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* fs-verity: read-only file-based authenticity protection
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*
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* Copyright 2019 Google LLC
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*/
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#ifndef _FSVERITY_PRIVATE_H
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#define _FSVERITY_PRIVATE_H
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#ifdef CONFIG_FS_VERITY_DEBUG
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#define DEBUG
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#endif
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#define pr_fmt(fmt) "fs-verity: " fmt
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#include <crypto/sha.h>
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#include <linux/fsverity.h>
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#include <linux/mempool.h>
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struct ahash_request;
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/*
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* Implementation limit: maximum depth of the Merkle tree. For now 8 is plenty;
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* it's enough for over U64_MAX bytes of data using SHA-256 and 4K blocks.
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*/
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#define FS_VERITY_MAX_LEVELS 8
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/*
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* Largest digest size among all hash algorithms supported by fs-verity.
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* Currently assumed to be <= size of fsverity_descriptor::root_hash.
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*/
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#define FS_VERITY_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE
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/* A hash algorithm supported by fs-verity */
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struct fsverity_hash_alg {
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struct crypto_ahash *tfm; /* hash tfm, allocated on demand */
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const char *name; /* crypto API name, e.g. sha256 */
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unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */
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unsigned int block_size; /* block size in bytes, e.g. 64 for SHA-256 */
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mempool_t req_pool; /* mempool with a preallocated hash request */
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};
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/* Merkle tree parameters: hash algorithm, initial hash state, and topology */
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struct merkle_tree_params {
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struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
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const u8 *hashstate; /* initial hash state or NULL */
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unsigned int digest_size; /* same as hash_alg->digest_size */
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unsigned int block_size; /* size of data and tree blocks */
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unsigned int hashes_per_block; /* number of hashes per tree block */
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unsigned int log_blocksize; /* log2(block_size) */
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unsigned int log_arity; /* log2(hashes_per_block) */
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unsigned int num_levels; /* number of levels in Merkle tree */
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u64 tree_size; /* Merkle tree size in bytes */
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unsigned long level0_blocks; /* number of blocks in tree level 0 */
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/*
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* Starting block index for each tree level, ordered from leaf level (0)
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* to root level ('num_levels - 1')
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*/
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u64 level_start[FS_VERITY_MAX_LEVELS];
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};
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/**
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* fsverity_info - cached verity metadata for an inode
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*
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* When a verity file is first opened, an instance of this struct is allocated
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* and stored in ->i_verity_info; it remains until the inode is evicted. It
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* caches information about the Merkle tree that's needed to efficiently verify
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* data read from the file. It also caches the file measurement. The Merkle
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* tree pages themselves are not cached here, but the filesystem may cache them.
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*/
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struct fsverity_info {
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struct merkle_tree_params tree_params;
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u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
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u8 measurement[FS_VERITY_MAX_DIGEST_SIZE];
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const struct inode *inode;
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};
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/*
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* Merkle tree properties. The file measurement is the hash of this structure
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* excluding the signature and with the sig_size field set to 0.
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*/
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struct fsverity_descriptor {
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__u8 version; /* must be 1 */
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__u8 hash_algorithm; /* Merkle tree hash algorithm */
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__u8 log_blocksize; /* log2 of size of data and tree blocks */
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__u8 salt_size; /* size of salt in bytes; 0 if none */
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__le32 sig_size; /* size of signature in bytes; 0 if none */
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__le64 data_size; /* size of file the Merkle tree is built over */
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__u8 root_hash[64]; /* Merkle tree root hash */
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__u8 salt[32]; /* salt prepended to each hashed block */
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__u8 __reserved[144]; /* must be 0's */
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__u8 signature[]; /* optional PKCS#7 signature */
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};
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/* Arbitrary limit to bound the kmalloc() size. Can be changed. */
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#define FS_VERITY_MAX_DESCRIPTOR_SIZE 16384
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#define FS_VERITY_MAX_SIGNATURE_SIZE (FS_VERITY_MAX_DESCRIPTOR_SIZE - \
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sizeof(struct fsverity_descriptor))
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/*
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* Format in which verity file measurements are signed. This is the same as
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* 'struct fsverity_digest', except here some magic bytes are prepended to
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* provide some context about what is being signed in case the same key is used
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* for non-fsverity purposes, and here the fields have fixed endianness.
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*/
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struct fsverity_signed_digest {
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char magic[8]; /* must be "FSVerity" */
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__le16 digest_algorithm;
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__le16 digest_size;
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__u8 digest[];
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};
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/* hash_algs.c */
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extern struct fsverity_hash_alg fsverity_hash_algs[];
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struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
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unsigned int num);
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struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,
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gfp_t gfp_flags);
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void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
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struct ahash_request *req);
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const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
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const u8 *salt, size_t salt_size);
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int fsverity_hash_page(const struct merkle_tree_params *params,
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const struct inode *inode,
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struct ahash_request *req, struct page *page, u8 *out);
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int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
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const void *data, size_t size, u8 *out);
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void __init fsverity_check_hash_algs(void);
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/* init.c */
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extern void __printf(3, 4) __cold
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fsverity_msg(const struct inode *inode, const char *level,
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const char *fmt, ...);
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#define fsverity_warn(inode, fmt, ...) \
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fsverity_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
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#define fsverity_err(inode, fmt, ...) \
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fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
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/* open.c */
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int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
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const struct inode *inode,
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unsigned int hash_algorithm,
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unsigned int log_blocksize,
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const u8 *salt, size_t salt_size);
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struct fsverity_info *fsverity_create_info(const struct inode *inode,
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void *desc, size_t desc_size);
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void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
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void fsverity_free_info(struct fsverity_info *vi);
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int __init fsverity_init_info_cache(void);
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void __init fsverity_exit_info_cache(void);
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/* signature.c */
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#ifdef CONFIG_FS_VERITY_BUILTIN_SIGNATURES
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int fsverity_verify_signature(const struct fsverity_info *vi,
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const struct fsverity_descriptor *desc,
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size_t desc_size);
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int __init fsverity_init_signature(void);
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#else /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
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static inline int
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fsverity_verify_signature(const struct fsverity_info *vi,
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const struct fsverity_descriptor *desc,
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size_t desc_size)
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{
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return 0;
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}
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static inline int fsverity_init_signature(void)
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{
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return 0;
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}
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#endif /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
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/* verify.c */
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int __init fsverity_init_workqueue(void);
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void __init fsverity_exit_workqueue(void);
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#endif /* _FSVERITY_PRIVATE_H */
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