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671e67b4 EB |
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 | }, | |
add890c9 EB |
20 | [FS_VERITY_HASH_ALG_SHA512] = { |
21 | .name = "sha512", | |
22 | .digest_size = SHA512_DIGEST_SIZE, | |
23 | .block_size = SHA512_BLOCK_SIZE, | |
24 | }, | |
671e67b4 EB |
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 | } |