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 #include <linux/scatterlist.h> 12 13 /* The hash algorithms supported by fs-verity */ 14 struct fsverity_hash_alg fsverity_hash_algs[] = { 15 [FS_VERITY_HASH_ALG_SHA256] = { 16 .name = "sha256", 17 .digest_size = SHA256_DIGEST_SIZE, 18 .block_size = SHA256_BLOCK_SIZE, 19 .algo_id = HASH_ALGO_SHA256, 20 }, 21 [FS_VERITY_HASH_ALG_SHA512] = { 22 .name = "sha512", 23 .digest_size = SHA512_DIGEST_SIZE, 24 .block_size = SHA512_BLOCK_SIZE, 25 .algo_id = HASH_ALGO_SHA512, 26 }, 27 }; 28 29 static DEFINE_MUTEX(fsverity_hash_alg_init_mutex); 30 31 /** 32 * fsverity_get_hash_alg() - validate and prepare a hash algorithm 33 * @inode: optional inode for logging purposes 34 * @num: the hash algorithm number 35 * 36 * Get the struct fsverity_hash_alg for the given hash algorithm number, and 37 * ensure it has a hash transform ready to go. The hash transforms are 38 * allocated on-demand so that we don't waste resources unnecessarily, and 39 * because the crypto modules may be initialized later than fs/verity/. 40 * 41 * Return: pointer to the hash alg on success, else an ERR_PTR() 42 */ 43 struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, 44 unsigned int num) 45 { 46 struct fsverity_hash_alg *alg; 47 struct crypto_ahash *tfm; 48 int err; 49 50 if (num >= ARRAY_SIZE(fsverity_hash_algs) || 51 !fsverity_hash_algs[num].name) { 52 fsverity_warn(inode, "Unknown hash algorithm number: %u", num); 53 return ERR_PTR(-EINVAL); 54 } 55 alg = &fsverity_hash_algs[num]; 56 57 /* pairs with smp_store_release() below */ 58 if (likely(smp_load_acquire(&alg->tfm) != NULL)) 59 return alg; 60 61 mutex_lock(&fsverity_hash_alg_init_mutex); 62 63 if (alg->tfm != NULL) 64 goto out_unlock; 65 66 /* 67 * Using the shash API would make things a bit simpler, but the ahash 68 * API is preferable as it allows the use of crypto accelerators. 69 */ 70 tfm = crypto_alloc_ahash(alg->name, 0, 0); 71 if (IS_ERR(tfm)) { 72 if (PTR_ERR(tfm) == -ENOENT) { 73 fsverity_warn(inode, 74 "Missing crypto API support for hash algorithm \"%s\"", 75 alg->name); 76 alg = ERR_PTR(-ENOPKG); 77 goto out_unlock; 78 } 79 fsverity_err(inode, 80 "Error allocating hash algorithm \"%s\": %ld", 81 alg->name, PTR_ERR(tfm)); 82 alg = ERR_CAST(tfm); 83 goto out_unlock; 84 } 85 86 err = -EINVAL; 87 if (WARN_ON_ONCE(alg->digest_size != crypto_ahash_digestsize(tfm))) 88 goto err_free_tfm; 89 if (WARN_ON_ONCE(alg->block_size != crypto_ahash_blocksize(tfm))) 90 goto err_free_tfm; 91 92 err = mempool_init_kmalloc_pool(&alg->req_pool, 1, 93 sizeof(struct ahash_request) + 94 crypto_ahash_reqsize(tfm)); 95 if (err) 96 goto err_free_tfm; 97 98 pr_info("%s using implementation \"%s\"\n", 99 alg->name, crypto_ahash_driver_name(tfm)); 100 101 /* pairs with smp_load_acquire() above */ 102 smp_store_release(&alg->tfm, tfm); 103 goto out_unlock; 104 105 err_free_tfm: 106 crypto_free_ahash(tfm); 107 alg = ERR_PTR(err); 108 out_unlock: 109 mutex_unlock(&fsverity_hash_alg_init_mutex); 110 return alg; 111 } 112 113 /** 114 * fsverity_alloc_hash_request() - allocate a hash request object 115 * @alg: the hash algorithm for which to allocate the request 116 * @gfp_flags: memory allocation flags 117 * 118 * This is mempool-backed, so this never fails if __GFP_DIRECT_RECLAIM is set in 119 * @gfp_flags. However, in that case this might need to wait for all 120 * previously-allocated requests to be freed. So to avoid deadlocks, callers 121 * must never need multiple requests at a time to make forward progress. 122 * 123 * Return: the request object on success; NULL on failure (but see above) 124 */ 125 struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg, 126 gfp_t gfp_flags) 127 { 128 struct ahash_request *req = mempool_alloc(&alg->req_pool, gfp_flags); 129 130 if (req) 131 ahash_request_set_tfm(req, alg->tfm); 132 return req; 133 } 134 135 /** 136 * fsverity_free_hash_request() - free a hash request object 137 * @alg: the hash algorithm 138 * @req: the hash request object to free 139 */ 140 void fsverity_free_hash_request(struct fsverity_hash_alg *alg, 141 struct ahash_request *req) 142 { 143 if (req) { 144 ahash_request_zero(req); 145 mempool_free(req, &alg->req_pool); 146 } 147 } 148 149 /** 150 * fsverity_prepare_hash_state() - precompute the initial hash state 151 * @alg: hash algorithm 152 * @salt: a salt which is to be prepended to all data to be hashed 153 * @salt_size: salt size in bytes, possibly 0 154 * 155 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed 156 * initial hash state on success or an ERR_PTR() on failure. 157 */ 158 const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg, 159 const u8 *salt, size_t salt_size) 160 { 161 u8 *hashstate = NULL; 162 struct ahash_request *req = NULL; 163 u8 *padded_salt = NULL; 164 size_t padded_salt_size; 165 struct scatterlist sg; 166 DECLARE_CRYPTO_WAIT(wait); 167 int err; 168 169 if (salt_size == 0) 170 return NULL; 171 172 hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL); 173 if (!hashstate) 174 return ERR_PTR(-ENOMEM); 175 176 /* This allocation never fails, since it's mempool-backed. */ 177 req = fsverity_alloc_hash_request(alg, GFP_KERNEL); 178 179 /* 180 * Zero-pad the salt to the next multiple of the input size of the hash 181 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128 182 * bytes for SHA-512. This ensures that the hash algorithm won't have 183 * any bytes buffered internally after processing the salt, thus making 184 * salted hashing just as fast as unsalted hashing. 185 */ 186 padded_salt_size = round_up(salt_size, alg->block_size); 187 padded_salt = kzalloc(padded_salt_size, GFP_KERNEL); 188 if (!padded_salt) { 189 err = -ENOMEM; 190 goto err_free; 191 } 192 memcpy(padded_salt, salt, salt_size); 193 194 sg_init_one(&sg, padded_salt, padded_salt_size); 195 ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | 196 CRYPTO_TFM_REQ_MAY_BACKLOG, 197 crypto_req_done, &wait); 198 ahash_request_set_crypt(req, &sg, NULL, padded_salt_size); 199 200 err = crypto_wait_req(crypto_ahash_init(req), &wait); 201 if (err) 202 goto err_free; 203 204 err = crypto_wait_req(crypto_ahash_update(req), &wait); 205 if (err) 206 goto err_free; 207 208 err = crypto_ahash_export(req, hashstate); 209 if (err) 210 goto err_free; 211 out: 212 fsverity_free_hash_request(alg, req); 213 kfree(padded_salt); 214 return hashstate; 215 216 err_free: 217 kfree(hashstate); 218 hashstate = ERR_PTR(err); 219 goto out; 220 } 221 222 /** 223 * fsverity_hash_block() - hash a single data or hash block 224 * @params: the Merkle tree's parameters 225 * @inode: inode for which the hashing is being done 226 * @req: preallocated hash request 227 * @page: the page containing the block to hash 228 * @offset: the offset of the block within @page 229 * @out: output digest, size 'params->digest_size' bytes 230 * 231 * Hash a single data or hash block. The hash is salted if a salt is specified 232 * in the Merkle tree parameters. 233 * 234 * Return: 0 on success, -errno on failure 235 */ 236 int fsverity_hash_block(const struct merkle_tree_params *params, 237 const struct inode *inode, struct ahash_request *req, 238 struct page *page, unsigned int offset, u8 *out) 239 { 240 struct scatterlist sg; 241 DECLARE_CRYPTO_WAIT(wait); 242 int err; 243 244 sg_init_table(&sg, 1); 245 sg_set_page(&sg, page, params->block_size, offset); 246 ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | 247 CRYPTO_TFM_REQ_MAY_BACKLOG, 248 crypto_req_done, &wait); 249 ahash_request_set_crypt(req, &sg, out, params->block_size); 250 251 if (params->hashstate) { 252 err = crypto_ahash_import(req, params->hashstate); 253 if (err) { 254 fsverity_err(inode, 255 "Error %d importing hash state", err); 256 return err; 257 } 258 err = crypto_ahash_finup(req); 259 } else { 260 err = crypto_ahash_digest(req); 261 } 262 263 err = crypto_wait_req(err, &wait); 264 if (err) 265 fsverity_err(inode, "Error %d computing block hash", err); 266 return err; 267 } 268 269 /** 270 * fsverity_hash_buffer() - hash some data 271 * @alg: the hash algorithm to use 272 * @data: the data to hash 273 * @size: size of data to hash, in bytes 274 * @out: output digest, size 'alg->digest_size' bytes 275 * 276 * Hash some data which is located in physically contiguous memory (i.e. memory 277 * allocated by kmalloc(), not by vmalloc()). No salt is used. 278 * 279 * Return: 0 on success, -errno on failure 280 */ 281 int fsverity_hash_buffer(struct fsverity_hash_alg *alg, 282 const void *data, size_t size, u8 *out) 283 { 284 struct ahash_request *req; 285 struct scatterlist sg; 286 DECLARE_CRYPTO_WAIT(wait); 287 int err; 288 289 /* This allocation never fails, since it's mempool-backed. */ 290 req = fsverity_alloc_hash_request(alg, GFP_KERNEL); 291 292 sg_init_one(&sg, data, size); 293 ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | 294 CRYPTO_TFM_REQ_MAY_BACKLOG, 295 crypto_req_done, &wait); 296 ahash_request_set_crypt(req, &sg, out, size); 297 298 err = crypto_wait_req(crypto_ahash_digest(req), &wait); 299 300 fsverity_free_hash_request(alg, req); 301 return err; 302 } 303 304 void __init fsverity_check_hash_algs(void) 305 { 306 size_t i; 307 308 /* 309 * Sanity check the hash algorithms (could be a build-time check, but 310 * they're in an array) 311 */ 312 for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) { 313 const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i]; 314 315 if (!alg->name) 316 continue; 317 318 BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE); 319 320 /* 321 * For efficiency, the implementation currently assumes the 322 * digest and block sizes are powers of 2. This limitation can 323 * be lifted if the code is updated to handle other values. 324 */ 325 BUG_ON(!is_power_of_2(alg->digest_size)); 326 BUG_ON(!is_power_of_2(alg->block_size)); 327 328 /* Verify that there is a valid mapping to HASH_ALGO_*. */ 329 BUG_ON(alg->algo_id == 0); 330 BUG_ON(alg->digest_size != hash_digest_size[alg->algo_id]); 331 } 332 } 333