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 }, 20 [FS_VERITY_HASH_ALG_SHA512] = { 21 .name = "sha512", 22 .digest_size = SHA512_DIGEST_SIZE, 23 .block_size = SHA512_BLOCK_SIZE, 24 }, 25 }; 26 27 static DEFINE_MUTEX(fsverity_hash_alg_init_mutex); 28 29 /** 30 * fsverity_get_hash_alg() - validate and prepare a hash algorithm 31 * @inode: optional inode for logging purposes 32 * @num: the hash algorithm number 33 * 34 * Get the struct fsverity_hash_alg for the given hash algorithm number, and 35 * ensure it has a hash transform ready to go. The hash transforms are 36 * allocated on-demand so that we don't waste resources unnecessarily, and 37 * because the crypto modules may be initialized later than fs/verity/. 38 * 39 * Return: pointer to the hash alg on success, else an ERR_PTR() 40 */ 41 struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, 42 unsigned int num) 43 { 44 struct fsverity_hash_alg *alg; 45 struct crypto_ahash *tfm; 46 int err; 47 48 if (num >= ARRAY_SIZE(fsverity_hash_algs) || 49 !fsverity_hash_algs[num].name) { 50 fsverity_warn(inode, "Unknown hash algorithm number: %u", num); 51 return ERR_PTR(-EINVAL); 52 } 53 alg = &fsverity_hash_algs[num]; 54 55 /* pairs with smp_store_release() below */ 56 if (likely(smp_load_acquire(&alg->tfm) != NULL)) 57 return alg; 58 59 mutex_lock(&fsverity_hash_alg_init_mutex); 60 61 if (alg->tfm != NULL) 62 goto out_unlock; 63 64 /* 65 * Using the shash API would make things a bit simpler, but the ahash 66 * API is preferable as it allows the use of crypto accelerators. 67 */ 68 tfm = crypto_alloc_ahash(alg->name, 0, 0); 69 if (IS_ERR(tfm)) { 70 if (PTR_ERR(tfm) == -ENOENT) { 71 fsverity_warn(inode, 72 "Missing crypto API support for hash algorithm \"%s\"", 73 alg->name); 74 alg = ERR_PTR(-ENOPKG); 75 goto out_unlock; 76 } 77 fsverity_err(inode, 78 "Error allocating hash algorithm \"%s\": %ld", 79 alg->name, PTR_ERR(tfm)); 80 alg = ERR_CAST(tfm); 81 goto out_unlock; 82 } 83 84 err = -EINVAL; 85 if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm))) 86 goto err_free_tfm; 87 if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm))) 88 goto err_free_tfm; 89 90 err = mempool_init_kmalloc_pool(&alg->req_pool, 1, 91 sizeof(struct ahash_request) + 92 crypto_ahash_reqsize(tfm)); 93 if (err) 94 goto err_free_tfm; 95 96 pr_info("%s using implementation \"%s\"\n", 97 alg->name, crypto_ahash_driver_name(tfm)); 98 99 /* pairs with smp_load_acquire() above */ 100 smp_store_release(&alg->tfm, tfm); 101 goto out_unlock; 102 103 err_free_tfm: 104 crypto_free_ahash(tfm); 105 alg = ERR_PTR(err); 106 out_unlock: 107 mutex_unlock(&fsverity_hash_alg_init_mutex); 108 return alg; 109 } 110 111 /** 112 * fsverity_alloc_hash_request() - allocate a hash request object 113 * @alg: the hash algorithm for which to allocate the request 114 * @gfp_flags: memory allocation flags 115 * 116 * This is mempool-backed, so this never fails if __GFP_DIRECT_RECLAIM is set in 117 * @gfp_flags. However, in that case this might need to wait for all 118 * previously-allocated requests to be freed. So to avoid deadlocks, callers 119 * must never need multiple requests at a time to make forward progress. 120 * 121 * Return: the request object on success; NULL on failure (but see above) 122 */ 123 struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg, 124 gfp_t gfp_flags) 125 { 126 struct ahash_request *req = mempool_alloc(&alg->req_pool, gfp_flags); 127 128 if (req) 129 ahash_request_set_tfm(req, alg->tfm); 130 return req; 131 } 132 133 /** 134 * fsverity_free_hash_request() - free a hash request object 135 * @alg: the hash algorithm 136 * @req: the hash request object to free 137 */ 138 void fsverity_free_hash_request(struct fsverity_hash_alg *alg, 139 struct ahash_request *req) 140 { 141 if (req) { 142 ahash_request_zero(req); 143 mempool_free(req, &alg->req_pool); 144 } 145 } 146 147 /** 148 * fsverity_prepare_hash_state() - precompute the initial hash state 149 * @alg: hash algorithm 150 * @salt: a salt which is to be prepended to all data to be hashed 151 * @salt_size: salt size in bytes, possibly 0 152 * 153 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed 154 * initial hash state on success or an ERR_PTR() on failure. 155 */ 156 const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg, 157 const u8 *salt, size_t salt_size) 158 { 159 u8 *hashstate = NULL; 160 struct ahash_request *req = NULL; 161 u8 *padded_salt = NULL; 162 size_t padded_salt_size; 163 struct scatterlist sg; 164 DECLARE_CRYPTO_WAIT(wait); 165 int err; 166 167 if (salt_size == 0) 168 return NULL; 169 170 hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL); 171 if (!hashstate) 172 return ERR_PTR(-ENOMEM); 173 174 /* This allocation never fails, since it's mempool-backed. */ 175 req = fsverity_alloc_hash_request(alg, GFP_KERNEL); 176 177 /* 178 * Zero-pad the salt to the next multiple of the input size of the hash 179 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128 180 * bytes for SHA-512. This ensures that the hash algorithm won't have 181 * any bytes buffered internally after processing the salt, thus making 182 * salted hashing just as fast as unsalted hashing. 183 */ 184 padded_salt_size = round_up(salt_size, alg->block_size); 185 padded_salt = kzalloc(padded_salt_size, GFP_KERNEL); 186 if (!padded_salt) { 187 err = -ENOMEM; 188 goto err_free; 189 } 190 memcpy(padded_salt, salt, salt_size); 191 192 sg_init_one(&sg, padded_salt, padded_salt_size); 193 ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | 194 CRYPTO_TFM_REQ_MAY_BACKLOG, 195 crypto_req_done, &wait); 196 ahash_request_set_crypt(req, &sg, NULL, padded_salt_size); 197 198 err = crypto_wait_req(crypto_ahash_init(req), &wait); 199 if (err) 200 goto err_free; 201 202 err = crypto_wait_req(crypto_ahash_update(req), &wait); 203 if (err) 204 goto err_free; 205 206 err = crypto_ahash_export(req, hashstate); 207 if (err) 208 goto err_free; 209 out: 210 fsverity_free_hash_request(alg, req); 211 kfree(padded_salt); 212 return hashstate; 213 214 err_free: 215 kfree(hashstate); 216 hashstate = ERR_PTR(err); 217 goto out; 218 } 219 220 /** 221 * fsverity_hash_page() - hash a single data or hash page 222 * @params: the Merkle tree's parameters 223 * @inode: inode for which the hashing is being done 224 * @req: preallocated hash request 225 * @page: the page to hash 226 * @out: output digest, size 'params->digest_size' bytes 227 * 228 * Hash a single data or hash block, assuming block_size == PAGE_SIZE. 229 * The hash is salted if a salt is specified in the Merkle tree parameters. 230 * 231 * Return: 0 on success, -errno on failure 232 */ 233 int fsverity_hash_page(const struct merkle_tree_params *params, 234 const struct inode *inode, 235 struct ahash_request *req, struct page *page, u8 *out) 236 { 237 struct scatterlist sg; 238 DECLARE_CRYPTO_WAIT(wait); 239 int err; 240 241 if (WARN_ON(params->block_size != PAGE_SIZE)) 242 return -EINVAL; 243 244 sg_init_table(&sg, 1); 245 sg_set_page(&sg, page, PAGE_SIZE, 0); 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, PAGE_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 page 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 } 329