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 */ 13struct 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 28int g_fsverity_hash_algs_num = ARRAY_SIZE(fsverity_hash_algs); 29 30static DEFINE_MUTEX(fsverity_hash_alg_init_mutex); 31 32/** 33 * fsverity_get_hash_alg() - validate and prepare a hash algorithm 34 * @inode: optional inode for logging purposes 35 * @num: the hash algorithm number 36 * 37 * Get the struct fsverity_hash_alg for the given hash algorithm number, and 38 * ensure it has a hash transform ready to go. The hash transforms are 39 * allocated on-demand so that we don't waste resources unnecessarily, and 40 * because the crypto modules may be initialized later than fs/verity/. 41 * 42 * Return: pointer to the hash alg on success, else an ERR_PTR() 43 */ 44const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, 45 unsigned int num) 46{ 47 struct fsverity_hash_alg *alg; 48 struct crypto_shash *tfm; 49 int err; 50 51 if (num >= ARRAY_SIZE(fsverity_hash_algs) || 52 !fsverity_hash_algs[num].name) { 53 fsverity_warn(inode, "Unknown hash algorithm number: %u", num); 54 return ERR_PTR(-EINVAL); 55 } 56 alg = &fsverity_hash_algs[num]; 57 58 /* pairs with smp_store_release() below */ 59 if (likely(smp_load_acquire(&alg->tfm) != NULL)) 60 return alg; 61 62 mutex_lock(&fsverity_hash_alg_init_mutex); 63 64 if (alg->tfm != NULL) 65 goto out_unlock; 66 67 tfm = crypto_alloc_shash(alg->name, 0, 0); 68 if (IS_ERR(tfm)) { 69 if (PTR_ERR(tfm) == -ENOENT) { 70 fsverity_warn(inode, 71 "Missing crypto API support for hash algorithm \"%s\"", 72 alg->name); 73 alg = ERR_PTR(-ENOPKG); 74 goto out_unlock; 75 } 76 fsverity_err(inode, 77 "Error allocating hash algorithm \"%s\": %ld", 78 alg->name, PTR_ERR(tfm)); 79 alg = ERR_CAST(tfm); 80 goto out_unlock; 81 } 82 83 err = -EINVAL; 84 if (WARN_ON_ONCE(alg->digest_size != crypto_shash_digestsize(tfm))) 85 goto err_free_tfm; 86 if (WARN_ON_ONCE(alg->block_size != crypto_shash_blocksize(tfm))) 87 goto err_free_tfm; 88 89 pr_info("%s using implementation \"%s\"\n", 90 alg->name, crypto_shash_driver_name(tfm)); 91 92 /* pairs with smp_load_acquire() above */ 93 smp_store_release(&alg->tfm, tfm); 94 goto out_unlock; 95 96err_free_tfm: 97 crypto_free_shash(tfm); 98 alg = ERR_PTR(err); 99out_unlock: 100 mutex_unlock(&fsverity_hash_alg_init_mutex); 101 return alg; 102} 103 104/** 105 * fsverity_prepare_hash_state() - precompute the initial hash state 106 * @alg: hash algorithm 107 * @salt: a salt which is to be prepended to all data to be hashed 108 * @salt_size: salt size in bytes, possibly 0 109 * 110 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed 111 * initial hash state on success or an ERR_PTR() on failure. 112 */ 113const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg, 114 const u8 *salt, size_t salt_size) 115{ 116 u8 *hashstate = NULL; 117 SHASH_DESC_ON_STACK(desc, alg->tfm); 118 u8 *padded_salt = NULL; 119 size_t padded_salt_size; 120 int err; 121 122 desc->tfm = alg->tfm; 123 124 if (salt_size == 0) 125 return NULL; 126 127 hashstate = kmalloc(crypto_shash_statesize(alg->tfm), GFP_KERNEL); 128 if (!hashstate) 129 return ERR_PTR(-ENOMEM); 130 131 /* 132 * Zero-pad the salt to the next multiple of the input size of the hash 133 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128 134 * bytes for SHA-512. This ensures that the hash algorithm won't have 135 * any bytes buffered internally after processing the salt, thus making 136 * salted hashing just as fast as unsalted hashing. 137 */ 138 padded_salt_size = round_up(salt_size, alg->block_size); 139 padded_salt = kzalloc(padded_salt_size, GFP_KERNEL); 140 if (!padded_salt) { 141 err = -ENOMEM; 142 goto err_free; 143 } 144 memcpy(padded_salt, salt, salt_size); 145 err = crypto_shash_init(desc); 146 if (err) 147 goto err_free; 148 149 err = crypto_shash_update(desc, padded_salt, padded_salt_size); 150 if (err) 151 goto err_free; 152 153 err = crypto_shash_export(desc, hashstate); 154 if (err) 155 goto err_free; 156out: 157 kfree(padded_salt); 158 return hashstate; 159 160err_free: 161 kfree(hashstate); 162 hashstate = ERR_PTR(err); 163 goto out; 164} 165 166/** 167 * fsverity_hash_block() - hash a single data or hash block 168 * @params: the Merkle tree's parameters 169 * @inode: inode for which the hashing is being done 170 * @data: virtual address of a buffer containing the block to hash 171 * @out: output digest, size 'params->digest_size' bytes 172 * 173 * Hash a single data or hash block. The hash is salted if a salt is specified 174 * in the Merkle tree parameters. 175 * 176 * Return: 0 on success, -errno on failure 177 */ 178int fsverity_hash_block(const struct merkle_tree_params *params, 179 const struct inode *inode, const void *data, u8 *out) 180{ 181 SHASH_DESC_ON_STACK(desc, params->hash_alg->tfm); 182 int err; 183 184 desc->tfm = params->hash_alg->tfm; 185 186 if (params->hashstate) { 187 err = crypto_shash_import(desc, params->hashstate); 188 if (err) { 189 fsverity_err(inode, 190 "Error %d importing hash state", err); 191 return err; 192 } 193 err = crypto_shash_finup(desc, data, params->block_size, out); 194 } else { 195 err = crypto_shash_digest(desc, data, params->block_size, out); 196 } 197 if (err) 198 fsverity_err(inode, "Error %d computing block hash", err); 199 return err; 200} 201 202/** 203 * fsverity_hash_buffer() - hash some data 204 * @alg: the hash algorithm to use 205 * @data: the data to hash 206 * @size: size of data to hash, in bytes 207 * @out: output digest, size 'alg->digest_size' bytes 208 * 209 * Return: 0 on success, -errno on failure 210 */ 211int fsverity_hash_buffer(const struct fsverity_hash_alg *alg, 212 const void *data, size_t size, u8 *out) 213{ 214 return crypto_shash_tfm_digest(alg->tfm, data, size, out); 215} 216 217void __init fsverity_check_hash_algs(void) 218{ 219 size_t i; 220 221 /* 222 * Sanity check the hash algorithms (could be a build-time check, but 223 * they're in an array) 224 */ 225 for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) { 226 const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i]; 227 228 if (!alg->name) 229 continue; 230 231 /* 232 * 0 must never be allocated as an FS_VERITY_HASH_ALG_* value, 233 * as it is reserved for users that use 0 to mean unspecified or 234 * a default value. fs/verity/ itself doesn't care and doesn't 235 * have a default algorithm, but some users make use of this. 236 */ 237 BUG_ON(i == 0); 238 239 BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE); 240 241 /* 242 * For efficiency, the implementation currently assumes the 243 * digest and block sizes are powers of 2. This limitation can 244 * be lifted if the code is updated to handle other values. 245 */ 246 BUG_ON(!is_power_of_2(alg->digest_size)); 247 BUG_ON(!is_power_of_2(alg->block_size)); 248 249 /* Verify that there is a valid mapping to HASH_ALGO_*. */ 250 BUG_ON(alg->algo_id == 0); 251 BUG_ON(alg->digest_size != hash_digest_size[alg->algo_id]); 252 } 253} 254