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1// SPDX-License-Identifier: GPL-2.02/*3 * fs-verity hash algorithms4 *5 * Copyright 2019 Google LLC6 */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 28static DEFINE_MUTEX(fsverity_hash_alg_init_mutex);29 30/**31 * fsverity_get_hash_alg() - validate and prepare a hash algorithm32 * @inode: optional inode for logging purposes33 * @num: the hash algorithm number34 *35 * Get the struct fsverity_hash_alg for the given hash algorithm number, and36 * ensure it has a hash transform ready to go. The hash transforms are37 * allocated on-demand so that we don't waste resources unnecessarily, and38 * 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 */42const 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 94err_free_tfm:95 crypto_free_shash(tfm);96 alg = ERR_PTR(err);97out_unlock:98 mutex_unlock(&fsverity_hash_alg_init_mutex);99 return alg;100}101 102/**103 * fsverity_prepare_hash_state() - precompute the initial hash state104 * @alg: hash algorithm105 * @salt: a salt which is to be prepended to all data to be hashed106 * @salt_size: salt size in bytes, possibly 0107 *108 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed109 * initial hash state on success or an ERR_PTR() on failure.110 */111const 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 hash131 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128132 * bytes for SHA-512. This ensures that the hash algorithm won't have133 * any bytes buffered internally after processing the salt, thus making134 * 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;154out:155 kfree(padded_salt);156 return hashstate;157 158err_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 block166 * @params: the Merkle tree's parameters167 * @inode: inode for which the hashing is being done168 * @data: virtual address of a buffer containing the block to hash169 * @out: output digest, size 'params->digest_size' bytes170 *171 * Hash a single data or hash block. The hash is salted if a salt is specified172 * in the Merkle tree parameters.173 *174 * Return: 0 on success, -errno on failure175 */176int 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 data202 * @alg: the hash algorithm to use203 * @data: the data to hash204 * @size: size of data to hash, in bytes205 * @out: output digest, size 'alg->digest_size' bytes206 *207 * Return: 0 on success, -errno on failure208 */209int 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 215void __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, but221 * 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 or232 * a default value. fs/verity/ itself doesn't care and doesn't233 * 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 the241 * digest and block sizes are powers of 2. This limitation can242 * 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