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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 | ||
439bea10 EB |
27 | static DEFINE_MUTEX(fsverity_hash_alg_init_mutex); |
28 | ||
671e67b4 EB |
29 | /** |
30 | * fsverity_get_hash_alg() - validate and prepare a hash algorithm | |
31 | * @inode: optional inode for logging purposes | |
32 | * @num: the hash algorithm number | |
33 | * | |
34 | * Get the struct fsverity_hash_alg for the given hash algorithm number, and | |
35 | * ensure it has a hash transform ready to go. The hash transforms are | |
36 | * allocated on-demand so that we don't waste resources unnecessarily, and | |
37 | * because the crypto modules may be initialized later than fs/verity/. | |
38 | * | |
39 | * Return: pointer to the hash alg on success, else an ERR_PTR() | |
40 | */ | |
439bea10 EB |
41 | struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, |
42 | unsigned int num) | |
671e67b4 EB |
43 | { |
44 | struct fsverity_hash_alg *alg; | |
45 | struct crypto_ahash *tfm; | |
46 | int err; | |
47 | ||
48 | if (num >= ARRAY_SIZE(fsverity_hash_algs) || | |
49 | !fsverity_hash_algs[num].name) { | |
50 | fsverity_warn(inode, "Unknown hash algorithm number: %u", num); | |
51 | return ERR_PTR(-EINVAL); | |
52 | } | |
53 | alg = &fsverity_hash_algs[num]; | |
54 | ||
439bea10 EB |
55 | /* pairs with smp_store_release() below */ |
56 | if (likely(smp_load_acquire(&alg->tfm) != NULL)) | |
671e67b4 | 57 | return alg; |
439bea10 EB |
58 | |
59 | mutex_lock(&fsverity_hash_alg_init_mutex); | |
60 | ||
61 | if (alg->tfm != NULL) | |
62 | goto out_unlock; | |
63 | ||
671e67b4 EB |
64 | /* |
65 | * Using the shash API would make things a bit simpler, but the ahash | |
66 | * API is preferable as it allows the use of crypto accelerators. | |
67 | */ | |
68 | tfm = crypto_alloc_ahash(alg->name, 0, 0); | |
69 | if (IS_ERR(tfm)) { | |
70 | if (PTR_ERR(tfm) == -ENOENT) { | |
71 | fsverity_warn(inode, | |
72 | "Missing crypto API support for hash algorithm \"%s\"", | |
73 | alg->name); | |
439bea10 EB |
74 | alg = ERR_PTR(-ENOPKG); |
75 | goto out_unlock; | |
671e67b4 EB |
76 | } |
77 | fsverity_err(inode, | |
78 | "Error allocating hash algorithm \"%s\": %ld", | |
79 | alg->name, PTR_ERR(tfm)); | |
439bea10 EB |
80 | alg = ERR_CAST(tfm); |
81 | goto out_unlock; | |
671e67b4 EB |
82 | } |
83 | ||
84 | err = -EINVAL; | |
85 | if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm))) | |
86 | goto err_free_tfm; | |
87 | if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm))) | |
88 | goto err_free_tfm; | |
89 | ||
439bea10 EB |
90 | err = mempool_init_kmalloc_pool(&alg->req_pool, 1, |
91 | sizeof(struct ahash_request) + | |
92 | crypto_ahash_reqsize(tfm)); | |
93 | if (err) | |
94 | goto err_free_tfm; | |
95 | ||
671e67b4 EB |
96 | pr_info("%s using implementation \"%s\"\n", |
97 | alg->name, crypto_ahash_driver_name(tfm)); | |
98 | ||
439bea10 EB |
99 | /* pairs with smp_load_acquire() above */ |
100 | smp_store_release(&alg->tfm, tfm); | |
101 | goto out_unlock; | |
671e67b4 EB |
102 | |
103 | err_free_tfm: | |
104 | crypto_free_ahash(tfm); | |
439bea10 EB |
105 | alg = ERR_PTR(err); |
106 | out_unlock: | |
107 | mutex_unlock(&fsverity_hash_alg_init_mutex); | |
108 | return alg; | |
109 | } | |
110 | ||
111 | /** | |
112 | * fsverity_alloc_hash_request() - allocate a hash request object | |
113 | * @alg: the hash algorithm for which to allocate the request | |
114 | * @gfp_flags: memory allocation flags | |
115 | * | |
116 | * This is mempool-backed, so this never fails if __GFP_DIRECT_RECLAIM is set in | |
117 | * @gfp_flags. However, in that case this might need to wait for all | |
118 | * previously-allocated requests to be freed. So to avoid deadlocks, callers | |
119 | * must never need multiple requests at a time to make forward progress. | |
120 | * | |
121 | * Return: the request object on success; NULL on failure (but see above) | |
122 | */ | |
123 | struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg, | |
124 | gfp_t gfp_flags) | |
125 | { | |
126 | struct ahash_request *req = mempool_alloc(&alg->req_pool, gfp_flags); | |
127 | ||
128 | if (req) | |
129 | ahash_request_set_tfm(req, alg->tfm); | |
130 | return req; | |
131 | } | |
132 | ||
133 | /** | |
134 | * fsverity_free_hash_request() - free a hash request object | |
135 | * @alg: the hash algorithm | |
136 | * @req: the hash request object to free | |
137 | */ | |
138 | void fsverity_free_hash_request(struct fsverity_hash_alg *alg, | |
139 | struct ahash_request *req) | |
140 | { | |
141 | if (req) { | |
142 | ahash_request_zero(req); | |
143 | mempool_free(req, &alg->req_pool); | |
144 | } | |
671e67b4 EB |
145 | } |
146 | ||
147 | /** | |
148 | * fsverity_prepare_hash_state() - precompute the initial hash state | |
149 | * @alg: hash algorithm | |
150 | * @salt: a salt which is to be prepended to all data to be hashed | |
151 | * @salt_size: salt size in bytes, possibly 0 | |
152 | * | |
153 | * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed | |
154 | * initial hash state on success or an ERR_PTR() on failure. | |
155 | */ | |
439bea10 | 156 | const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg, |
671e67b4 EB |
157 | const u8 *salt, size_t salt_size) |
158 | { | |
159 | u8 *hashstate = NULL; | |
160 | struct ahash_request *req = NULL; | |
161 | u8 *padded_salt = NULL; | |
162 | size_t padded_salt_size; | |
163 | struct scatterlist sg; | |
164 | DECLARE_CRYPTO_WAIT(wait); | |
165 | int err; | |
166 | ||
167 | if (salt_size == 0) | |
168 | return NULL; | |
169 | ||
170 | hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL); | |
171 | if (!hashstate) | |
172 | return ERR_PTR(-ENOMEM); | |
173 | ||
439bea10 EB |
174 | /* This allocation never fails, since it's mempool-backed. */ |
175 | req = fsverity_alloc_hash_request(alg, GFP_KERNEL); | |
671e67b4 EB |
176 | |
177 | /* | |
178 | * Zero-pad the salt to the next multiple of the input size of the hash | |
179 | * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128 | |
180 | * bytes for SHA-512. This ensures that the hash algorithm won't have | |
181 | * any bytes buffered internally after processing the salt, thus making | |
182 | * salted hashing just as fast as unsalted hashing. | |
183 | */ | |
184 | padded_salt_size = round_up(salt_size, alg->block_size); | |
185 | padded_salt = kzalloc(padded_salt_size, GFP_KERNEL); | |
186 | if (!padded_salt) { | |
187 | err = -ENOMEM; | |
188 | goto err_free; | |
189 | } | |
190 | memcpy(padded_salt, salt, salt_size); | |
191 | ||
192 | sg_init_one(&sg, padded_salt, padded_salt_size); | |
193 | ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | | |
194 | CRYPTO_TFM_REQ_MAY_BACKLOG, | |
195 | crypto_req_done, &wait); | |
196 | ahash_request_set_crypt(req, &sg, NULL, padded_salt_size); | |
197 | ||
198 | err = crypto_wait_req(crypto_ahash_init(req), &wait); | |
199 | if (err) | |
200 | goto err_free; | |
201 | ||
202 | err = crypto_wait_req(crypto_ahash_update(req), &wait); | |
203 | if (err) | |
204 | goto err_free; | |
205 | ||
206 | err = crypto_ahash_export(req, hashstate); | |
207 | if (err) | |
208 | goto err_free; | |
209 | out: | |
439bea10 | 210 | fsverity_free_hash_request(alg, req); |
671e67b4 EB |
211 | kfree(padded_salt); |
212 | return hashstate; | |
213 | ||
214 | err_free: | |
215 | kfree(hashstate); | |
216 | hashstate = ERR_PTR(err); | |
217 | goto out; | |
218 | } | |
219 | ||
220 | /** | |
221 | * fsverity_hash_page() - hash a single data or hash page | |
222 | * @params: the Merkle tree's parameters | |
223 | * @inode: inode for which the hashing is being done | |
224 | * @req: preallocated hash request | |
225 | * @page: the page to hash | |
226 | * @out: output digest, size 'params->digest_size' bytes | |
227 | * | |
228 | * Hash a single data or hash block, assuming block_size == PAGE_SIZE. | |
229 | * The hash is salted if a salt is specified in the Merkle tree parameters. | |
230 | * | |
231 | * Return: 0 on success, -errno on failure | |
232 | */ | |
233 | int fsverity_hash_page(const struct merkle_tree_params *params, | |
234 | const struct inode *inode, | |
235 | struct ahash_request *req, struct page *page, u8 *out) | |
236 | { | |
237 | struct scatterlist sg; | |
238 | DECLARE_CRYPTO_WAIT(wait); | |
239 | int err; | |
240 | ||
241 | if (WARN_ON(params->block_size != PAGE_SIZE)) | |
242 | return -EINVAL; | |
243 | ||
244 | sg_init_table(&sg, 1); | |
245 | sg_set_page(&sg, page, PAGE_SIZE, 0); | |
246 | ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | | |
247 | CRYPTO_TFM_REQ_MAY_BACKLOG, | |
248 | crypto_req_done, &wait); | |
249 | ahash_request_set_crypt(req, &sg, out, PAGE_SIZE); | |
250 | ||
251 | if (params->hashstate) { | |
252 | err = crypto_ahash_import(req, params->hashstate); | |
253 | if (err) { | |
254 | fsverity_err(inode, | |
255 | "Error %d importing hash state", err); | |
256 | return err; | |
257 | } | |
258 | err = crypto_ahash_finup(req); | |
259 | } else { | |
260 | err = crypto_ahash_digest(req); | |
261 | } | |
262 | ||
263 | err = crypto_wait_req(err, &wait); | |
264 | if (err) | |
265 | fsverity_err(inode, "Error %d computing page hash", err); | |
266 | return err; | |
267 | } | |
268 | ||
269 | /** | |
270 | * fsverity_hash_buffer() - hash some data | |
271 | * @alg: the hash algorithm to use | |
272 | * @data: the data to hash | |
273 | * @size: size of data to hash, in bytes | |
274 | * @out: output digest, size 'alg->digest_size' bytes | |
275 | * | |
276 | * Hash some data which is located in physically contiguous memory (i.e. memory | |
277 | * allocated by kmalloc(), not by vmalloc()). No salt is used. | |
278 | * | |
279 | * Return: 0 on success, -errno on failure | |
280 | */ | |
439bea10 | 281 | int fsverity_hash_buffer(struct fsverity_hash_alg *alg, |
671e67b4 EB |
282 | const void *data, size_t size, u8 *out) |
283 | { | |
284 | struct ahash_request *req; | |
285 | struct scatterlist sg; | |
286 | DECLARE_CRYPTO_WAIT(wait); | |
287 | int err; | |
288 | ||
439bea10 EB |
289 | /* This allocation never fails, since it's mempool-backed. */ |
290 | req = fsverity_alloc_hash_request(alg, GFP_KERNEL); | |
671e67b4 EB |
291 | |
292 | sg_init_one(&sg, data, size); | |
293 | ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | | |
294 | CRYPTO_TFM_REQ_MAY_BACKLOG, | |
295 | crypto_req_done, &wait); | |
296 | ahash_request_set_crypt(req, &sg, out, size); | |
297 | ||
298 | err = crypto_wait_req(crypto_ahash_digest(req), &wait); | |
299 | ||
439bea10 | 300 | fsverity_free_hash_request(alg, req); |
671e67b4 EB |
301 | return err; |
302 | } | |
303 | ||
304 | void __init fsverity_check_hash_algs(void) | |
305 | { | |
306 | size_t i; | |
307 | ||
308 | /* | |
309 | * Sanity check the hash algorithms (could be a build-time check, but | |
310 | * they're in an array) | |
311 | */ | |
312 | for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) { | |
313 | const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i]; | |
314 | ||
315 | if (!alg->name) | |
316 | continue; | |
317 | ||
318 | BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE); | |
319 | ||
320 | /* | |
321 | * For efficiency, the implementation currently assumes the | |
322 | * digest and block sizes are powers of 2. This limitation can | |
323 | * be lifted if the code is updated to handle other values. | |
324 | */ | |
325 | BUG_ON(!is_power_of_2(alg->digest_size)); | |
326 | BUG_ON(!is_power_of_2(alg->block_size)); | |
327 | } | |
328 | } |