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 */
13 struct 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
28 static DEFINE_MUTEX(fsverity_hash_alg_init_mutex);
29
30 /**
31 * fsverity_get_hash_alg() - validate and prepare a hash algorithm
32 * @inode: optional inode for logging purposes
33 * @num: the hash algorithm number
34 *
35 * Get the struct fsverity_hash_alg for the given hash algorithm number, and
36 * ensure it has a hash transform ready to go. The hash transforms are
37 * allocated on-demand so that we don't waste resources unnecessarily, and
38 * 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 */
fsverity_get_hash_alg(const struct inode * inode,unsigned int num)42 const 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 alg->mb_max_msgs = min(crypto_shash_mb_max_msgs(tfm),
88 FS_VERITY_MAX_PENDING_DATA_BLOCKS);
89
90 pr_info("%s using implementation \"%s\"%s\n",
91 alg->name, crypto_shash_driver_name(tfm),
92 alg->mb_max_msgs > 1 ? " (multibuffer)" : "");
93
94 /* pairs with smp_load_acquire() above */
95 smp_store_release(&alg->tfm, tfm);
96 goto out_unlock;
97
98 err_free_tfm:
99 crypto_free_shash(tfm);
100 alg = ERR_PTR(err);
101 out_unlock:
102 mutex_unlock(&fsverity_hash_alg_init_mutex);
103 return alg;
104 }
105
106 /**
107 * fsverity_prepare_hash_state() - precompute the initial hash state
108 * @alg: hash algorithm
109 * @salt: a salt which is to be prepended to all data to be hashed
110 * @salt_size: salt size in bytes, possibly 0
111 *
112 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed
113 * initial hash state on success or an ERR_PTR() on failure.
114 */
fsverity_prepare_hash_state(const struct fsverity_hash_alg * alg,const u8 * salt,size_t salt_size)115 const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
116 const u8 *salt, size_t salt_size)
117 {
118 u8 *hashstate = NULL;
119 SHASH_DESC_ON_STACK(desc, alg->tfm);
120 u8 *padded_salt = NULL;
121 size_t padded_salt_size;
122 int err;
123
124 desc->tfm = alg->tfm;
125
126 if (salt_size == 0)
127 return NULL;
128
129 hashstate = kmalloc(crypto_shash_statesize(alg->tfm), GFP_KERNEL);
130 if (!hashstate)
131 return ERR_PTR(-ENOMEM);
132
133 /*
134 * Zero-pad the salt to the next multiple of the input size of the hash
135 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128
136 * bytes for SHA-512. This ensures that the hash algorithm won't have
137 * any bytes buffered internally after processing the salt, thus making
138 * salted hashing just as fast as unsalted hashing.
139 */
140 padded_salt_size = round_up(salt_size, alg->block_size);
141 padded_salt = kzalloc(padded_salt_size, GFP_KERNEL);
142 if (!padded_salt) {
143 err = -ENOMEM;
144 goto err_free;
145 }
146 memcpy(padded_salt, salt, salt_size);
147 err = crypto_shash_init(desc);
148 if (err)
149 goto err_free;
150
151 err = crypto_shash_update(desc, padded_salt, padded_salt_size);
152 if (err)
153 goto err_free;
154
155 err = crypto_shash_export(desc, hashstate);
156 if (err)
157 goto err_free;
158 out:
159 kfree(padded_salt);
160 return hashstate;
161
162 err_free:
163 kfree(hashstate);
164 hashstate = ERR_PTR(err);
165 goto out;
166 }
167
168 /**
169 * fsverity_hash_block() - hash a single data or hash block
170 * @params: the Merkle tree's parameters
171 * @inode: inode for which the hashing is being done
172 * @data: virtual address of a buffer containing the block to hash
173 * @out: output digest, size 'params->digest_size' bytes
174 *
175 * Hash a single data or hash block. The hash is salted if a salt is specified
176 * in the Merkle tree parameters.
177 *
178 * Return: 0 on success, -errno on failure
179 */
fsverity_hash_block(const struct merkle_tree_params * params,const struct inode * inode,const void * data,u8 * out)180 int fsverity_hash_block(const struct merkle_tree_params *params,
181 const struct inode *inode, const void *data, u8 *out)
182 {
183 SHASH_DESC_ON_STACK(desc, params->hash_alg->tfm);
184 int err;
185
186 desc->tfm = params->hash_alg->tfm;
187
188 if (params->hashstate) {
189 err = crypto_shash_import(desc, params->hashstate);
190 if (err) {
191 fsverity_err(inode,
192 "Error %d importing hash state", err);
193 return err;
194 }
195 err = crypto_shash_finup(desc, data, params->block_size, out);
196 } else {
197 err = crypto_shash_digest(desc, data, params->block_size, out);
198 }
199 if (err)
200 fsverity_err(inode, "Error %d computing block hash", err);
201 return err;
202 }
203
204 /**
205 * fsverity_hash_buffer() - hash some data
206 * @alg: the hash algorithm to use
207 * @data: the data to hash
208 * @size: size of data to hash, in bytes
209 * @out: output digest, size 'alg->digest_size' bytes
210 *
211 * Return: 0 on success, -errno on failure
212 */
fsverity_hash_buffer(const struct fsverity_hash_alg * alg,const void * data,size_t size,u8 * out)213 int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
214 const void *data, size_t size, u8 *out)
215 {
216 return crypto_shash_tfm_digest(alg->tfm, data, size, out);
217 }
218
fsverity_check_hash_algs(void)219 void __init fsverity_check_hash_algs(void)
220 {
221 size_t i;
222
223 /*
224 * Sanity check the hash algorithms (could be a build-time check, but
225 * they're in an array)
226 */
227 for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) {
228 const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i];
229
230 if (!alg->name)
231 continue;
232
233 /*
234 * 0 must never be allocated as an FS_VERITY_HASH_ALG_* value,
235 * as it is reserved for users that use 0 to mean unspecified or
236 * a default value. fs/verity/ itself doesn't care and doesn't
237 * have a default algorithm, but some users make use of this.
238 */
239 BUG_ON(i == 0);
240
241 BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE);
242
243 /*
244 * For efficiency, the implementation currently assumes the
245 * digest and block sizes are powers of 2. This limitation can
246 * be lifted if the code is updated to handle other values.
247 */
248 BUG_ON(!is_power_of_2(alg->digest_size));
249 BUG_ON(!is_power_of_2(alg->block_size));
250
251 /* Verify that there is a valid mapping to HASH_ALGO_*. */
252 BUG_ON(alg->algo_id == 0);
253 BUG_ON(alg->digest_size != hash_digest_size[alg->algo_id]);
254 }
255 }
256