1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* 3 * fs-verity: read-only file-based authenticity protection 4 * 5 * Copyright 2019 Google LLC 6 */ 7 8 #ifndef _FSVERITY_PRIVATE_H 9 #define _FSVERITY_PRIVATE_H 10 11 #ifdef CONFIG_FS_VERITY_DEBUG 12 #define DEBUG 13 #endif 14 15 #define pr_fmt(fmt) "fs-verity: " fmt 16 17 #include <crypto/sha.h> 18 #include <linux/fsverity.h> 19 20 struct ahash_request; 21 22 /* 23 * Implementation limit: maximum depth of the Merkle tree. For now 8 is plenty; 24 * it's enough for over U64_MAX bytes of data using SHA-256 and 4K blocks. 25 */ 26 #define FS_VERITY_MAX_LEVELS 8 27 28 /* 29 * Largest digest size among all hash algorithms supported by fs-verity. 30 * Currently assumed to be <= size of fsverity_descriptor::root_hash. 31 */ 32 #define FS_VERITY_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE 33 34 /* A hash algorithm supported by fs-verity */ 35 struct fsverity_hash_alg { 36 struct crypto_ahash *tfm; /* hash tfm, allocated on demand */ 37 const char *name; /* crypto API name, e.g. sha256 */ 38 unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */ 39 unsigned int block_size; /* block size in bytes, e.g. 64 for SHA-256 */ 40 }; 41 42 /* Merkle tree parameters: hash algorithm, initial hash state, and topology */ 43 struct merkle_tree_params { 44 const struct fsverity_hash_alg *hash_alg; /* the hash algorithm */ 45 const u8 *hashstate; /* initial hash state or NULL */ 46 unsigned int digest_size; /* same as hash_alg->digest_size */ 47 unsigned int block_size; /* size of data and tree blocks */ 48 unsigned int hashes_per_block; /* number of hashes per tree block */ 49 unsigned int log_blocksize; /* log2(block_size) */ 50 unsigned int log_arity; /* log2(hashes_per_block) */ 51 unsigned int num_levels; /* number of levels in Merkle tree */ 52 u64 tree_size; /* Merkle tree size in bytes */ 53 54 /* 55 * Starting block index for each tree level, ordered from leaf level (0) 56 * to root level ('num_levels - 1') 57 */ 58 u64 level_start[FS_VERITY_MAX_LEVELS]; 59 }; 60 61 /** 62 * fsverity_info - cached verity metadata for an inode 63 * 64 * When a verity file is first opened, an instance of this struct is allocated 65 * and stored in ->i_verity_info; it remains until the inode is evicted. It 66 * caches information about the Merkle tree that's needed to efficiently verify 67 * data read from the file. It also caches the file measurement. The Merkle 68 * tree pages themselves are not cached here, but the filesystem may cache them. 69 */ 70 struct fsverity_info { 71 struct merkle_tree_params tree_params; 72 u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE]; 73 u8 measurement[FS_VERITY_MAX_DIGEST_SIZE]; 74 const struct inode *inode; 75 }; 76 77 /* 78 * Merkle tree properties. The file measurement is the hash of this structure 79 * excluding the signature and with the sig_size field set to 0. 80 */ 81 struct fsverity_descriptor { 82 __u8 version; /* must be 1 */ 83 __u8 hash_algorithm; /* Merkle tree hash algorithm */ 84 __u8 log_blocksize; /* log2 of size of data and tree blocks */ 85 __u8 salt_size; /* size of salt in bytes; 0 if none */ 86 __le32 sig_size; /* size of signature in bytes; 0 if none */ 87 __le64 data_size; /* size of file the Merkle tree is built over */ 88 __u8 root_hash[64]; /* Merkle tree root hash */ 89 __u8 salt[32]; /* salt prepended to each hashed block */ 90 __u8 __reserved[144]; /* must be 0's */ 91 __u8 signature[]; /* optional PKCS#7 signature */ 92 }; 93 94 /* Arbitrary limit to bound the kmalloc() size. Can be changed. */ 95 #define FS_VERITY_MAX_DESCRIPTOR_SIZE 16384 96 97 #define FS_VERITY_MAX_SIGNATURE_SIZE (FS_VERITY_MAX_DESCRIPTOR_SIZE - \ 98 sizeof(struct fsverity_descriptor)) 99 100 /* 101 * Format in which verity file measurements are signed. This is the same as 102 * 'struct fsverity_digest', except here some magic bytes are prepended to 103 * provide some context about what is being signed in case the same key is used 104 * for non-fsverity purposes, and here the fields have fixed endianness. 105 */ 106 struct fsverity_signed_digest { 107 char magic[8]; /* must be "FSVerity" */ 108 __le16 digest_algorithm; 109 __le16 digest_size; 110 __u8 digest[]; 111 }; 112 113 /* hash_algs.c */ 114 115 extern struct fsverity_hash_alg fsverity_hash_algs[]; 116 117 const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, 118 unsigned int num); 119 const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg, 120 const u8 *salt, size_t salt_size); 121 int fsverity_hash_page(const struct merkle_tree_params *params, 122 const struct inode *inode, 123 struct ahash_request *req, struct page *page, u8 *out); 124 int fsverity_hash_buffer(const struct fsverity_hash_alg *alg, 125 const void *data, size_t size, u8 *out); 126 void __init fsverity_check_hash_algs(void); 127 128 /* init.c */ 129 130 extern void __printf(3, 4) __cold 131 fsverity_msg(const struct inode *inode, const char *level, 132 const char *fmt, ...); 133 134 #define fsverity_warn(inode, fmt, ...) \ 135 fsverity_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__) 136 #define fsverity_err(inode, fmt, ...) \ 137 fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__) 138 139 /* open.c */ 140 141 int fsverity_init_merkle_tree_params(struct merkle_tree_params *params, 142 const struct inode *inode, 143 unsigned int hash_algorithm, 144 unsigned int log_blocksize, 145 const u8 *salt, size_t salt_size); 146 147 struct fsverity_info *fsverity_create_info(const struct inode *inode, 148 void *desc, size_t desc_size); 149 150 void fsverity_set_info(struct inode *inode, struct fsverity_info *vi); 151 152 void fsverity_free_info(struct fsverity_info *vi); 153 154 int __init fsverity_init_info_cache(void); 155 void __init fsverity_exit_info_cache(void); 156 157 /* signature.c */ 158 159 #ifdef CONFIG_FS_VERITY_BUILTIN_SIGNATURES 160 int fsverity_verify_signature(const struct fsverity_info *vi, 161 const struct fsverity_descriptor *desc, 162 size_t desc_size); 163 164 int __init fsverity_init_signature(void); 165 #else /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */ 166 static inline int 167 fsverity_verify_signature(const struct fsverity_info *vi, 168 const struct fsverity_descriptor *desc, 169 size_t desc_size) 170 { 171 return 0; 172 } 173 174 static inline int fsverity_init_signature(void) 175 { 176 return 0; 177 } 178 #endif /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */ 179 180 /* verify.c */ 181 182 int __init fsverity_init_workqueue(void); 183 void __init fsverity_exit_workqueue(void); 184 185 #endif /* _FSVERITY_PRIVATE_H */ 186