1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * fs/verity/hash_algs.c: 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 /** 28 * fsverity_get_hash_alg() - validate and prepare a hash algorithm 29 * @inode: optional inode for logging purposes 30 * @num: the hash algorithm number 31 * 32 * Get the struct fsverity_hash_alg for the given hash algorithm number, and 33 * ensure it has a hash transform ready to go. The hash transforms are 34 * allocated on-demand so that we don't waste resources unnecessarily, and 35 * because the crypto modules may be initialized later than fs/verity/. 36 * 37 * Return: pointer to the hash alg on success, else an ERR_PTR() 38 */ 39 const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, 40 unsigned int num) 41 { 42 struct fsverity_hash_alg *alg; 43 struct crypto_ahash *tfm; 44 int err; 45 46 if (num >= ARRAY_SIZE(fsverity_hash_algs) || 47 !fsverity_hash_algs[num].name) { 48 fsverity_warn(inode, "Unknown hash algorithm number: %u", num); 49 return ERR_PTR(-EINVAL); 50 } 51 alg = &fsverity_hash_algs[num]; 52 53 /* pairs with cmpxchg() below */ 54 tfm = READ_ONCE(alg->tfm); 55 if (likely(tfm != NULL)) 56 return alg; 57 /* 58 * Using the shash API would make things a bit simpler, but the ahash 59 * API is preferable as it allows the use of crypto accelerators. 60 */ 61 tfm = crypto_alloc_ahash(alg->name, 0, 0); 62 if (IS_ERR(tfm)) { 63 if (PTR_ERR(tfm) == -ENOENT) { 64 fsverity_warn(inode, 65 "Missing crypto API support for hash algorithm \"%s\"", 66 alg->name); 67 return ERR_PTR(-ENOPKG); 68 } 69 fsverity_err(inode, 70 "Error allocating hash algorithm \"%s\": %ld", 71 alg->name, PTR_ERR(tfm)); 72 return ERR_CAST(tfm); 73 } 74 75 err = -EINVAL; 76 if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm))) 77 goto err_free_tfm; 78 if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm))) 79 goto err_free_tfm; 80 81 pr_info("%s using implementation \"%s\"\n", 82 alg->name, crypto_ahash_driver_name(tfm)); 83 84 /* pairs with READ_ONCE() above */ 85 if (cmpxchg(&alg->tfm, NULL, tfm) != NULL) 86 crypto_free_ahash(tfm); 87 88 return alg; 89 90 err_free_tfm: 91 crypto_free_ahash(tfm); 92 return ERR_PTR(err); 93 } 94 95 /** 96 * fsverity_prepare_hash_state() - precompute the initial hash state 97 * @alg: hash algorithm 98 * @salt: a salt which is to be prepended to all data to be hashed 99 * @salt_size: salt size in bytes, possibly 0 100 * 101 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed 102 * initial hash state on success or an ERR_PTR() on failure. 103 */ 104 const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg, 105 const u8 *salt, size_t salt_size) 106 { 107 u8 *hashstate = NULL; 108 struct ahash_request *req = NULL; 109 u8 *padded_salt = NULL; 110 size_t padded_salt_size; 111 struct scatterlist sg; 112 DECLARE_CRYPTO_WAIT(wait); 113 int err; 114 115 if (salt_size == 0) 116 return NULL; 117 118 hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL); 119 if (!hashstate) 120 return ERR_PTR(-ENOMEM); 121 122 req = ahash_request_alloc(alg->tfm, GFP_KERNEL); 123 if (!req) { 124 err = -ENOMEM; 125 goto err_free; 126 } 127 128 /* 129 * Zero-pad the salt to the next multiple of the input size of the hash 130 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128 131 * bytes for SHA-512. This ensures that the hash algorithm won't have 132 * any bytes buffered internally after processing the salt, thus making 133 * salted hashing just as fast as unsalted hashing. 134 */ 135 padded_salt_size = round_up(salt_size, alg->block_size); 136 padded_salt = kzalloc(padded_salt_size, GFP_KERNEL); 137 if (!padded_salt) { 138 err = -ENOMEM; 139 goto err_free; 140 } 141 memcpy(padded_salt, salt, salt_size); 142 143 sg_init_one(&sg, padded_salt, padded_salt_size); 144 ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | 145 CRYPTO_TFM_REQ_MAY_BACKLOG, 146 crypto_req_done, &wait); 147 ahash_request_set_crypt(req, &sg, NULL, padded_salt_size); 148 149 err = crypto_wait_req(crypto_ahash_init(req), &wait); 150 if (err) 151 goto err_free; 152 153 err = crypto_wait_req(crypto_ahash_update(req), &wait); 154 if (err) 155 goto err_free; 156 157 err = crypto_ahash_export(req, hashstate); 158 if (err) 159 goto err_free; 160 out: 161 ahash_request_free(req); 162 kfree(padded_salt); 163 return hashstate; 164 165 err_free: 166 kfree(hashstate); 167 hashstate = ERR_PTR(err); 168 goto out; 169 } 170 171 /** 172 * fsverity_hash_page() - hash a single data or hash page 173 * @params: the Merkle tree's parameters 174 * @inode: inode for which the hashing is being done 175 * @req: preallocated hash request 176 * @page: the page to hash 177 * @out: output digest, size 'params->digest_size' bytes 178 * 179 * Hash a single data or hash block, assuming block_size == PAGE_SIZE. 180 * The hash is salted if a salt is specified in the Merkle tree parameters. 181 * 182 * Return: 0 on success, -errno on failure 183 */ 184 int fsverity_hash_page(const struct merkle_tree_params *params, 185 const struct inode *inode, 186 struct ahash_request *req, struct page *page, u8 *out) 187 { 188 struct scatterlist sg; 189 DECLARE_CRYPTO_WAIT(wait); 190 int err; 191 192 if (WARN_ON(params->block_size != PAGE_SIZE)) 193 return -EINVAL; 194 195 sg_init_table(&sg, 1); 196 sg_set_page(&sg, page, PAGE_SIZE, 0); 197 ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | 198 CRYPTO_TFM_REQ_MAY_BACKLOG, 199 crypto_req_done, &wait); 200 ahash_request_set_crypt(req, &sg, out, PAGE_SIZE); 201 202 if (params->hashstate) { 203 err = crypto_ahash_import(req, params->hashstate); 204 if (err) { 205 fsverity_err(inode, 206 "Error %d importing hash state", err); 207 return err; 208 } 209 err = crypto_ahash_finup(req); 210 } else { 211 err = crypto_ahash_digest(req); 212 } 213 214 err = crypto_wait_req(err, &wait); 215 if (err) 216 fsverity_err(inode, "Error %d computing page hash", err); 217 return err; 218 } 219 220 /** 221 * fsverity_hash_buffer() - hash some data 222 * @alg: the hash algorithm to use 223 * @data: the data to hash 224 * @size: size of data to hash, in bytes 225 * @out: output digest, size 'alg->digest_size' bytes 226 * 227 * Hash some data which is located in physically contiguous memory (i.e. memory 228 * allocated by kmalloc(), not by vmalloc()). No salt is used. 229 * 230 * Return: 0 on success, -errno on failure 231 */ 232 int fsverity_hash_buffer(const struct fsverity_hash_alg *alg, 233 const void *data, size_t size, u8 *out) 234 { 235 struct ahash_request *req; 236 struct scatterlist sg; 237 DECLARE_CRYPTO_WAIT(wait); 238 int err; 239 240 req = ahash_request_alloc(alg->tfm, GFP_KERNEL); 241 if (!req) 242 return -ENOMEM; 243 244 sg_init_one(&sg, data, size); 245 ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | 246 CRYPTO_TFM_REQ_MAY_BACKLOG, 247 crypto_req_done, &wait); 248 ahash_request_set_crypt(req, &sg, out, size); 249 250 err = crypto_wait_req(crypto_ahash_digest(req), &wait); 251 252 ahash_request_free(req); 253 return err; 254 } 255 256 void __init fsverity_check_hash_algs(void) 257 { 258 size_t i; 259 260 /* 261 * Sanity check the hash algorithms (could be a build-time check, but 262 * they're in an array) 263 */ 264 for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) { 265 const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i]; 266 267 if (!alg->name) 268 continue; 269 270 BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE); 271 272 /* 273 * For efficiency, the implementation currently assumes the 274 * digest and block sizes are powers of 2. This limitation can 275 * be lifted if the code is updated to handle other values. 276 */ 277 BUG_ON(!is_power_of_2(alg->digest_size)); 278 BUG_ON(!is_power_of_2(alg->block_size)); 279 } 280 } 281