1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * fs-verity hash algorithms 4 * 5 * Copyright 2019 Google LLC 6 */ 7 8 #include "fsverity_private.h" 9 10 #include <crypto/hash.h> 11 12 /* The hash algorithms supported by fs-verity */ 13 struct fsverity_hash_alg fsverity_hash_algs[] = { 14 [FS_VERITY_HASH_ALG_SHA256] = { 15 .name = "sha256", 16 .digest_size = SHA256_DIGEST_SIZE, 17 .block_size = SHA256_BLOCK_SIZE, 18 .algo_id = HASH_ALGO_SHA256, 19 }, 20 [FS_VERITY_HASH_ALG_SHA512] = { 21 .name = "sha512", 22 .digest_size = SHA512_DIGEST_SIZE, 23 .block_size = SHA512_BLOCK_SIZE, 24 .algo_id = HASH_ALGO_SHA512, 25 }, 26 }; 27 28 static DEFINE_MUTEX(fsverity_hash_alg_init_mutex); 29 30 /** 31 * fsverity_get_hash_alg() - validate and prepare a hash algorithm 32 * @inode: optional inode for logging purposes 33 * @num: the hash algorithm number 34 * 35 * Get the struct fsverity_hash_alg for the given hash algorithm number, and 36 * ensure it has a hash transform ready to go. The hash transforms are 37 * allocated on-demand so that we don't waste resources unnecessarily, and 38 * because the crypto modules may be initialized later than fs/verity/. 39 * 40 * Return: pointer to the hash alg on success, else an ERR_PTR() 41 */ 42 const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, 43 unsigned int num) 44 { 45 struct fsverity_hash_alg *alg; 46 struct crypto_shash *tfm; 47 int err; 48 49 if (num >= ARRAY_SIZE(fsverity_hash_algs) || 50 !fsverity_hash_algs[num].name) { 51 fsverity_warn(inode, "Unknown hash algorithm number: %u", num); 52 return ERR_PTR(-EINVAL); 53 } 54 alg = &fsverity_hash_algs[num]; 55 56 /* pairs with smp_store_release() below */ 57 if (likely(smp_load_acquire(&alg->tfm) != NULL)) 58 return alg; 59 60 mutex_lock(&fsverity_hash_alg_init_mutex); 61 62 if (alg->tfm != NULL) 63 goto out_unlock; 64 65 tfm = crypto_alloc_shash(alg->name, 0, 0); 66 if (IS_ERR(tfm)) { 67 if (PTR_ERR(tfm) == -ENOENT) { 68 fsverity_warn(inode, 69 "Missing crypto API support for hash algorithm \"%s\"", 70 alg->name); 71 alg = ERR_PTR(-ENOPKG); 72 goto out_unlock; 73 } 74 fsverity_err(inode, 75 "Error allocating hash algorithm \"%s\": %ld", 76 alg->name, PTR_ERR(tfm)); 77 alg = ERR_CAST(tfm); 78 goto out_unlock; 79 } 80 81 err = -EINVAL; 82 if (WARN_ON_ONCE(alg->digest_size != crypto_shash_digestsize(tfm))) 83 goto err_free_tfm; 84 if (WARN_ON_ONCE(alg->block_size != crypto_shash_blocksize(tfm))) 85 goto err_free_tfm; 86 87 pr_info("%s using implementation \"%s\"\n", 88 alg->name, crypto_shash_driver_name(tfm)); 89 90 /* pairs with smp_load_acquire() above */ 91 smp_store_release(&alg->tfm, tfm); 92 goto out_unlock; 93 94 err_free_tfm: 95 crypto_free_shash(tfm); 96 alg = ERR_PTR(err); 97 out_unlock: 98 mutex_unlock(&fsverity_hash_alg_init_mutex); 99 return alg; 100 } 101 102 /** 103 * fsverity_prepare_hash_state() - precompute the initial hash state 104 * @alg: hash algorithm 105 * @salt: a salt which is to be prepended to all data to be hashed 106 * @salt_size: salt size in bytes, possibly 0 107 * 108 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed 109 * initial hash state on success or an ERR_PTR() on failure. 110 */ 111 const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg, 112 const u8 *salt, size_t salt_size) 113 { 114 u8 *hashstate = NULL; 115 SHASH_DESC_ON_STACK(desc, alg->tfm); 116 u8 *padded_salt = NULL; 117 size_t padded_salt_size; 118 int err; 119 120 desc->tfm = alg->tfm; 121 122 if (salt_size == 0) 123 return NULL; 124 125 hashstate = kmalloc(crypto_shash_statesize(alg->tfm), GFP_KERNEL); 126 if (!hashstate) 127 return ERR_PTR(-ENOMEM); 128 129 /* 130 * Zero-pad the salt to the next multiple of the input size of the hash 131 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128 132 * bytes for SHA-512. This ensures that the hash algorithm won't have 133 * any bytes buffered internally after processing the salt, thus making 134 * salted hashing just as fast as unsalted hashing. 135 */ 136 padded_salt_size = round_up(salt_size, alg->block_size); 137 padded_salt = kzalloc(padded_salt_size, GFP_KERNEL); 138 if (!padded_salt) { 139 err = -ENOMEM; 140 goto err_free; 141 } 142 memcpy(padded_salt, salt, salt_size); 143 err = crypto_shash_init(desc); 144 if (err) 145 goto err_free; 146 147 err = crypto_shash_update(desc, padded_salt, padded_salt_size); 148 if (err) 149 goto err_free; 150 151 err = crypto_shash_export(desc, hashstate); 152 if (err) 153 goto err_free; 154 out: 155 kfree(padded_salt); 156 return hashstate; 157 158 err_free: 159 kfree(hashstate); 160 hashstate = ERR_PTR(err); 161 goto out; 162 } 163 164 /** 165 * fsverity_hash_block() - hash a single data or hash block 166 * @params: the Merkle tree's parameters 167 * @inode: inode for which the hashing is being done 168 * @data: virtual address of a buffer containing the block to hash 169 * @out: output digest, size 'params->digest_size' bytes 170 * 171 * Hash a single data or hash block. The hash is salted if a salt is specified 172 * in the Merkle tree parameters. 173 * 174 * Return: 0 on success, -errno on failure 175 */ 176 int fsverity_hash_block(const struct merkle_tree_params *params, 177 const struct inode *inode, const void *data, u8 *out) 178 { 179 SHASH_DESC_ON_STACK(desc, params->hash_alg->tfm); 180 int err; 181 182 desc->tfm = params->hash_alg->tfm; 183 184 if (params->hashstate) { 185 err = crypto_shash_import(desc, params->hashstate); 186 if (err) { 187 fsverity_err(inode, 188 "Error %d importing hash state", err); 189 return err; 190 } 191 err = crypto_shash_finup(desc, data, params->block_size, out); 192 } else { 193 err = crypto_shash_digest(desc, data, params->block_size, out); 194 } 195 if (err) 196 fsverity_err(inode, "Error %d computing block hash", err); 197 return err; 198 } 199 200 /** 201 * fsverity_hash_buffer() - hash some data 202 * @alg: the hash algorithm to use 203 * @data: the data to hash 204 * @size: size of data to hash, in bytes 205 * @out: output digest, size 'alg->digest_size' bytes 206 * 207 * Return: 0 on success, -errno on failure 208 */ 209 int fsverity_hash_buffer(const struct fsverity_hash_alg *alg, 210 const void *data, size_t size, u8 *out) 211 { 212 return crypto_shash_tfm_digest(alg->tfm, data, size, out); 213 } 214 215 void __init fsverity_check_hash_algs(void) 216 { 217 size_t i; 218 219 /* 220 * Sanity check the hash algorithms (could be a build-time check, but 221 * they're in an array) 222 */ 223 for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) { 224 const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i]; 225 226 if (!alg->name) 227 continue; 228 229 /* 230 * 0 must never be allocated as an FS_VERITY_HASH_ALG_* value, 231 * as it is reserved for users that use 0 to mean unspecified or 232 * a default value. fs/verity/ itself doesn't care and doesn't 233 * have a default algorithm, but some users make use of this. 234 */ 235 BUG_ON(i == 0); 236 237 BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE); 238 239 /* 240 * For efficiency, the implementation currently assumes the 241 * digest and block sizes are powers of 2. This limitation can 242 * be lifted if the code is updated to handle other values. 243 */ 244 BUG_ON(!is_power_of_2(alg->digest_size)); 245 BUG_ON(!is_power_of_2(alg->block_size)); 246 247 /* Verify that there is a valid mapping to HASH_ALGO_*. */ 248 BUG_ON(alg->algo_id == 0); 249 BUG_ON(alg->digest_size != hash_digest_size[alg->algo_id]); 250 } 251 } 252