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 #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 .algo_id = HASH_ALGO_SHA256,
20 },
21 [FS_VERITY_HASH_ALG_SHA512] = {
22 .name = "sha512",
23 .digest_size = SHA512_DIGEST_SIZE,
24 .block_size = SHA512_BLOCK_SIZE,
25 .algo_id = HASH_ALGO_SHA512,
26 },
27 };
28
29 static DEFINE_MUTEX(fsverity_hash_alg_init_mutex);
30
31 /**
32 * fsverity_get_hash_alg() - validate and prepare a hash algorithm
33 * @inode: optional inode for logging purposes
34 * @num: the hash algorithm number
35 *
36 * Get the struct fsverity_hash_alg for the given hash algorithm number, and
37 * ensure it has a hash transform ready to go. The hash transforms are
38 * allocated on-demand so that we don't waste resources unnecessarily, and
39 * because the crypto modules may be initialized later than fs/verity/.
40 *
41 * Return: pointer to the hash alg on success, else an ERR_PTR()
42 */
fsverity_get_hash_alg(const struct inode * inode,unsigned int num)43 struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
44 unsigned int num)
45 {
46 struct fsverity_hash_alg *alg;
47 struct crypto_ahash *tfm;
48 int err;
49
50 if (num >= ARRAY_SIZE(fsverity_hash_algs) ||
51 !fsverity_hash_algs[num].name) {
52 fsverity_warn(inode, "Unknown hash algorithm number: %u", num);
53 return ERR_PTR(-EINVAL);
54 }
55 alg = &fsverity_hash_algs[num];
56
57 /* pairs with smp_store_release() below */
58 if (likely(smp_load_acquire(&alg->tfm) != NULL))
59 return alg;
60
61 mutex_lock(&fsverity_hash_alg_init_mutex);
62
63 if (alg->tfm != NULL)
64 goto out_unlock;
65
66 /*
67 * Using the shash API would make things a bit simpler, but the ahash
68 * API is preferable as it allows the use of crypto accelerators.
69 */
70 tfm = crypto_alloc_ahash(alg->name, 0, 0);
71 if (IS_ERR(tfm)) {
72 if (PTR_ERR(tfm) == -ENOENT) {
73 fsverity_warn(inode,
74 "Missing crypto API support for hash algorithm \"%s\"",
75 alg->name);
76 alg = ERR_PTR(-ENOPKG);
77 goto out_unlock;
78 }
79 fsverity_err(inode,
80 "Error allocating hash algorithm \"%s\": %ld",
81 alg->name, PTR_ERR(tfm));
82 alg = ERR_CAST(tfm);
83 goto out_unlock;
84 }
85
86 err = -EINVAL;
87 if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm)))
88 goto err_free_tfm;
89 if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm)))
90 goto err_free_tfm;
91
92 err = mempool_init_kmalloc_pool(&alg->req_pool, 1,
93 sizeof(struct ahash_request) +
94 crypto_ahash_reqsize(tfm));
95 if (err)
96 goto err_free_tfm;
97
98 pr_info("%s using implementation \"%s\"\n",
99 alg->name, crypto_ahash_driver_name(tfm));
100
101 /* pairs with smp_load_acquire() above */
102 smp_store_release(&alg->tfm, tfm);
103 goto out_unlock;
104
105 err_free_tfm:
106 crypto_free_ahash(tfm);
107 alg = ERR_PTR(err);
108 out_unlock:
109 mutex_unlock(&fsverity_hash_alg_init_mutex);
110 return alg;
111 }
112
113 /**
114 * fsverity_alloc_hash_request() - allocate a hash request object
115 * @alg: the hash algorithm for which to allocate the request
116 * @gfp_flags: memory allocation flags
117 *
118 * This is mempool-backed, so this never fails if __GFP_DIRECT_RECLAIM is set in
119 * @gfp_flags. However, in that case this might need to wait for all
120 * previously-allocated requests to be freed. So to avoid deadlocks, callers
121 * must never need multiple requests at a time to make forward progress.
122 *
123 * Return: the request object on success; NULL on failure (but see above)
124 */
fsverity_alloc_hash_request(struct fsverity_hash_alg * alg,gfp_t gfp_flags)125 struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,
126 gfp_t gfp_flags)
127 {
128 struct ahash_request *req = mempool_alloc(&alg->req_pool, gfp_flags);
129
130 if (req)
131 ahash_request_set_tfm(req, alg->tfm);
132 return req;
133 }
134
135 /**
136 * fsverity_free_hash_request() - free a hash request object
137 * @alg: the hash algorithm
138 * @req: the hash request object to free
139 */
fsverity_free_hash_request(struct fsverity_hash_alg * alg,struct ahash_request * req)140 void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
141 struct ahash_request *req)
142 {
143 if (req) {
144 ahash_request_zero(req);
145 mempool_free(req, &alg->req_pool);
146 }
147 }
148
149 /**
150 * fsverity_prepare_hash_state() - precompute the initial hash state
151 * @alg: hash algorithm
152 * @salt: a salt which is to be prepended to all data to be hashed
153 * @salt_size: salt size in bytes, possibly 0
154 *
155 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed
156 * initial hash state on success or an ERR_PTR() on failure.
157 */
fsverity_prepare_hash_state(struct fsverity_hash_alg * alg,const u8 * salt,size_t salt_size)158 const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
159 const u8 *salt, size_t salt_size)
160 {
161 u8 *hashstate = NULL;
162 struct ahash_request *req = NULL;
163 u8 *padded_salt = NULL;
164 size_t padded_salt_size;
165 struct scatterlist sg;
166 DECLARE_CRYPTO_WAIT(wait);
167 int err;
168
169 if (salt_size == 0)
170 return NULL;
171
172 hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL);
173 if (!hashstate)
174 return ERR_PTR(-ENOMEM);
175
176 /* This allocation never fails, since it's mempool-backed. */
177 req = fsverity_alloc_hash_request(alg, GFP_KERNEL);
178
179 /*
180 * Zero-pad the salt to the next multiple of the input size of the hash
181 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128
182 * bytes for SHA-512. This ensures that the hash algorithm won't have
183 * any bytes buffered internally after processing the salt, thus making
184 * salted hashing just as fast as unsalted hashing.
185 */
186 padded_salt_size = round_up(salt_size, alg->block_size);
187 padded_salt = kzalloc(padded_salt_size, GFP_KERNEL);
188 if (!padded_salt) {
189 err = -ENOMEM;
190 goto err_free;
191 }
192 memcpy(padded_salt, salt, salt_size);
193
194 sg_init_one(&sg, padded_salt, padded_salt_size);
195 ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
196 CRYPTO_TFM_REQ_MAY_BACKLOG,
197 crypto_req_done, &wait);
198 ahash_request_set_crypt(req, &sg, NULL, padded_salt_size);
199
200 err = crypto_wait_req(crypto_ahash_init(req), &wait);
201 if (err)
202 goto err_free;
203
204 err = crypto_wait_req(crypto_ahash_update(req), &wait);
205 if (err)
206 goto err_free;
207
208 err = crypto_ahash_export(req, hashstate);
209 if (err)
210 goto err_free;
211 out:
212 fsverity_free_hash_request(alg, req);
213 kfree(padded_salt);
214 return hashstate;
215
216 err_free:
217 kfree(hashstate);
218 hashstate = ERR_PTR(err);
219 goto out;
220 }
221
222 /**
223 * fsverity_hash_block() - hash a single data or hash block
224 * @params: the Merkle tree's parameters
225 * @inode: inode for which the hashing is being done
226 * @req: preallocated hash request
227 * @page: the page containing the block to hash
228 * @offset: the offset of the block within @page
229 * @out: output digest, size 'params->digest_size' bytes
230 *
231 * Hash a single data or hash block. The hash is salted if a salt is specified
232 * in the Merkle tree parameters.
233 *
234 * Return: 0 on success, -errno on failure
235 */
fsverity_hash_block(const struct merkle_tree_params * params,const struct inode * inode,struct ahash_request * req,struct page * page,unsigned int offset,u8 * out)236 int fsverity_hash_block(const struct merkle_tree_params *params,
237 const struct inode *inode, struct ahash_request *req,
238 struct page *page, unsigned int offset, u8 *out)
239 {
240 struct scatterlist sg;
241 DECLARE_CRYPTO_WAIT(wait);
242 int err;
243
244 sg_init_table(&sg, 1);
245 sg_set_page(&sg, page, params->block_size, offset);
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, params->block_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 block 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 */
fsverity_hash_buffer(struct fsverity_hash_alg * alg,const void * data,size_t size,u8 * out)281 int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
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
289 /* This allocation never fails, since it's mempool-backed. */
290 req = fsverity_alloc_hash_request(alg, GFP_KERNEL);
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
300 fsverity_free_hash_request(alg, req);
301 return err;
302 }
303
fsverity_check_hash_algs(void)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 /* Verify that there is a valid mapping to HASH_ALGO_*. */
329 BUG_ON(alg->algo_id == 0);
330 BUG_ON(alg->digest_size != hash_digest_size[alg->algo_id]);
331 }
332 }
333