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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Opening fs-verity files
4 *
5 * Copyright 2019 Google LLC
6 */
7
8#include "fsverity_private.h"
9
10#include <linux/export.h>
11#include <linux/mm.h>
12#include <linux/slab.h>
13
14static struct kmem_cache *fsverity_info_cachep;
15static struct rhashtable fsverity_info_hash;
16
17static const struct rhashtable_params fsverity_info_hash_params = {
18 .key_len = sizeof_field(struct fsverity_info, inode),
19 .key_offset = offsetof(struct fsverity_info, inode),
20 .head_offset = offsetof(struct fsverity_info, rhash_head),
21 .automatic_shrinking = true,
22};
23
24/**
25 * fsverity_init_merkle_tree_params() - initialize Merkle tree parameters
26 * @params: the parameters struct to initialize
27 * @inode: the inode for which the Merkle tree is being built
28 * @hash_algorithm: number of hash algorithm to use
29 * @log_blocksize: log base 2 of block size to use
30 * @salt: pointer to salt (optional)
31 * @salt_size: size of salt, possibly 0
32 *
33 * Validate the hash algorithm and block size, then compute the tree topology
34 * (num levels, num blocks in each level, etc.) and initialize @params.
35 *
36 * Return: 0 on success, -errno on failure
37 */
38int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
39 const struct inode *inode,
40 unsigned int hash_algorithm,
41 unsigned int log_blocksize,
42 const u8 *salt, size_t salt_size)
43{
44 const struct fsverity_hash_alg *hash_alg;
45 int err;
46 u64 blocks;
47 u64 blocks_in_level[FS_VERITY_MAX_LEVELS];
48 u64 offset;
49 int level;
50
51 memset(params, 0, sizeof(*params));
52
53 hash_alg = fsverity_get_hash_alg(inode, hash_algorithm);
54 if (!hash_alg)
55 return -EINVAL;
56 params->hash_alg = hash_alg;
57 params->digest_size = hash_alg->digest_size;
58
59 if (salt_size) {
60 params->hashstate =
61 fsverity_prepare_hash_state(hash_alg, salt, salt_size);
62 if (!params->hashstate) {
63 err = -ENOMEM;
64 goto out_err;
65 }
66 }
67
68 /*
69 * fs/verity/ directly assumes that the Merkle tree block size is a
70 * power of 2 less than or equal to PAGE_SIZE. Another restriction
71 * arises from the interaction between fs/verity/ and the filesystems
72 * themselves: filesystems expect to be able to verify a single
73 * filesystem block of data at a time. Therefore, the Merkle tree block
74 * size must also be less than or equal to the filesystem block size.
75 *
76 * The above are the only hard limitations, so in theory the Merkle tree
77 * block size could be as small as twice the digest size. However,
78 * that's not useful, and it would result in some unusually deep and
79 * large Merkle trees. So we currently require that the Merkle tree
80 * block size be at least 1024 bytes. That's small enough to test the
81 * sub-page block case on systems with 4K pages, but not too small.
82 */
83 if (log_blocksize < 10 || log_blocksize > PAGE_SHIFT ||
84 log_blocksize > inode->i_blkbits) {
85 fsverity_warn(inode, "Unsupported log_blocksize: %u",
86 log_blocksize);
87 err = -EINVAL;
88 goto out_err;
89 }
90 params->log_blocksize = log_blocksize;
91 params->block_size = 1 << log_blocksize;
92 params->log_blocks_per_page = PAGE_SHIFT - log_blocksize;
93 params->blocks_per_page = 1 << params->log_blocks_per_page;
94
95 if (WARN_ON_ONCE(!is_power_of_2(params->digest_size))) {
96 err = -EINVAL;
97 goto out_err;
98 }
99 if (params->block_size < 2 * params->digest_size) {
100 fsverity_warn(inode,
101 "Merkle tree block size (%u) too small for hash algorithm \"%s\"",
102 params->block_size, hash_alg->name);
103 err = -EINVAL;
104 goto out_err;
105 }
106 params->log_digestsize = ilog2(params->digest_size);
107 params->log_arity = log_blocksize - params->log_digestsize;
108 params->hashes_per_block = 1 << params->log_arity;
109
110 /*
111 * Compute the number of levels in the Merkle tree and create a map from
112 * level to the starting block of that level. Level 'num_levels - 1' is
113 * the root and is stored first. Level 0 is the level directly "above"
114 * the data blocks and is stored last.
115 */
116
117 /* Compute number of levels and the number of blocks in each level */
118 blocks = ((u64)inode->i_size + params->block_size - 1) >> log_blocksize;
119 while (blocks > 1) {
120 if (params->num_levels >= FS_VERITY_MAX_LEVELS) {
121 fsverity_err(inode, "Too many levels in Merkle tree");
122 err = -EFBIG;
123 goto out_err;
124 }
125 blocks = (blocks + params->hashes_per_block - 1) >>
126 params->log_arity;
127 blocks_in_level[params->num_levels++] = blocks;
128 }
129
130 /* Compute the starting block of each level */
131 offset = 0;
132 for (level = (int)params->num_levels - 1; level >= 0; level--) {
133 params->level_start[level] = offset;
134 offset += blocks_in_level[level];
135 }
136
137 /*
138 * With block_size != PAGE_SIZE, an in-memory bitmap will need to be
139 * allocated to track the "verified" status of hash blocks. Don't allow
140 * this bitmap to get too large. For now, limit it to 1 MiB, which
141 * limits the file size to about 4.4 TB with SHA-256 and 4K blocks.
142 *
143 * Together with the fact that the data, and thus also the Merkle tree,
144 * cannot have more than ULONG_MAX pages, this implies that hash block
145 * indices can always fit in an 'unsigned long'. But to be safe, we
146 * explicitly check for that too. Note, this is only for hash block
147 * indices; data block indices might not fit in an 'unsigned long'.
148 */
149 if ((params->block_size != PAGE_SIZE && offset > 1 << 23) ||
150 offset > ULONG_MAX) {
151 fsverity_err(inode, "Too many blocks in Merkle tree");
152 err = -EFBIG;
153 goto out_err;
154 }
155
156 fsverity_hash_block(params, page_address(ZERO_PAGE(0)),
157 params->zero_digest);
158
159 params->tree_size = offset << log_blocksize;
160 params->tree_pages = PAGE_ALIGN(params->tree_size) >> PAGE_SHIFT;
161 return 0;
162
163out_err:
164 kfree(params->hashstate);
165 memset(params, 0, sizeof(*params));
166 return err;
167}
168
169/*
170 * Compute the file digest by hashing the fsverity_descriptor excluding the
171 * builtin signature and with the sig_size field set to 0.
172 */
173static void compute_file_digest(const struct fsverity_hash_alg *hash_alg,
174 struct fsverity_descriptor *desc,
175 u8 *file_digest)
176{
177 __le32 sig_size = desc->sig_size;
178
179 desc->sig_size = 0;
180 fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), file_digest);
181 desc->sig_size = sig_size;
182}
183
184/*
185 * Create a new fsverity_info from the given fsverity_descriptor (with optional
186 * appended builtin signature), and check the signature if present. The
187 * fsverity_descriptor must have already undergone basic validation.
188 */
189struct fsverity_info *fsverity_create_info(struct inode *inode,
190 struct fsverity_descriptor *desc)
191{
192 struct fsverity_info *vi;
193 int err;
194
195 vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL);
196 if (!vi)
197 return ERR_PTR(-ENOMEM);
198 vi->inode = inode;
199
200 err = fsverity_init_merkle_tree_params(&vi->tree_params, inode,
201 desc->hash_algorithm,
202 desc->log_blocksize,
203 desc->salt, desc->salt_size);
204 if (err) {
205 fsverity_err(inode,
206 "Error %d initializing Merkle tree parameters",
207 err);
208 goto fail;
209 }
210
211 memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
212
213 compute_file_digest(vi->tree_params.hash_alg, desc, vi->file_digest);
214
215 err = fsverity_verify_signature(vi, desc->signature,
216 le32_to_cpu(desc->sig_size));
217 if (err)
218 goto fail;
219
220 if (vi->tree_params.block_size != PAGE_SIZE) {
221 /*
222 * When the Merkle tree block size and page size differ, we use
223 * a bitmap to keep track of which hash blocks have been
224 * verified. This bitmap must contain one bit per hash block,
225 * including alignment to a page boundary at the end.
226 *
227 * Eventually, to support extremely large files in an efficient
228 * way, it might be necessary to make pages of this bitmap
229 * reclaimable. But for now, simply allocating the whole bitmap
230 * is a simple solution that works well on the files on which
231 * fsverity is realistically used. E.g., with SHA-256 and 4K
232 * blocks, a 100MB file only needs a 24-byte bitmap, and the
233 * bitmap for any file under 17GB fits in a 4K page.
234 */
235 unsigned long num_bits =
236 vi->tree_params.tree_pages <<
237 vi->tree_params.log_blocks_per_page;
238
239 vi->hash_block_verified = kvcalloc(BITS_TO_LONGS(num_bits),
240 sizeof(unsigned long),
241 GFP_KERNEL);
242 if (!vi->hash_block_verified) {
243 err = -ENOMEM;
244 goto fail;
245 }
246 }
247
248 return vi;
249
250fail:
251 fsverity_free_info(vi);
252 return ERR_PTR(err);
253}
254
255int fsverity_set_info(struct fsverity_info *vi)
256{
257 return rhashtable_lookup_insert_fast(&fsverity_info_hash,
258 &vi->rhash_head,
259 fsverity_info_hash_params);
260}
261
262struct fsverity_info *__fsverity_get_info(const struct inode *inode)
263{
264 return rhashtable_lookup_fast(&fsverity_info_hash, &inode,
265 fsverity_info_hash_params);
266}
267EXPORT_SYMBOL_GPL(__fsverity_get_info);
268
269static bool validate_fsverity_descriptor(struct inode *inode,
270 const struct fsverity_descriptor *desc,
271 size_t desc_size)
272{
273 if (desc_size < sizeof(*desc)) {
274 fsverity_err(inode, "Unrecognized descriptor size: %zu bytes",
275 desc_size);
276 return false;
277 }
278
279 if (desc->version != 1) {
280 fsverity_err(inode, "Unrecognized descriptor version: %u",
281 desc->version);
282 return false;
283 }
284
285 if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
286 fsverity_err(inode, "Reserved bits set in descriptor");
287 return false;
288 }
289
290 if (desc->salt_size > sizeof(desc->salt)) {
291 fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
292 return false;
293 }
294
295 if (le64_to_cpu(desc->data_size) != inode->i_size) {
296 fsverity_err(inode,
297 "Wrong data_size: %llu (desc) != %lld (inode)",
298 le64_to_cpu(desc->data_size), inode->i_size);
299 return false;
300 }
301
302 if (le32_to_cpu(desc->sig_size) > desc_size - sizeof(*desc)) {
303 fsverity_err(inode, "Signature overflows verity descriptor");
304 return false;
305 }
306
307 return true;
308}
309
310/*
311 * Read the inode's fsverity_descriptor (with optional appended builtin
312 * signature) from the filesystem, and do basic validation of it.
313 */
314int fsverity_get_descriptor(struct inode *inode,
315 struct fsverity_descriptor **desc_ret)
316{
317 int res;
318 struct fsverity_descriptor *desc;
319
320 res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0);
321 if (res < 0) {
322 fsverity_err(inode,
323 "Error %d getting verity descriptor size", res);
324 return res;
325 }
326 if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
327 fsverity_err(inode, "Verity descriptor is too large (%d bytes)",
328 res);
329 return -EMSGSIZE;
330 }
331 desc = kmalloc(res, GFP_KERNEL);
332 if (!desc)
333 return -ENOMEM;
334 res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res);
335 if (res < 0) {
336 fsverity_err(inode, "Error %d reading verity descriptor", res);
337 kfree(desc);
338 return res;
339 }
340
341 if (!validate_fsverity_descriptor(inode, desc, res)) {
342 kfree(desc);
343 return -EINVAL;
344 }
345
346 *desc_ret = desc;
347 return 0;
348}
349
350/**
351 * fsverity_ensure_verity_info() - cache verity info if it's not already cached
352 * @inode: the inode for which verity info should be cached
353 *
354 * Ensure this inode has verity info attached to it, it's assumed the inode
355 * already has fsverity enabled. Read fsverity descriptor and creates verity
356 * based on that.
357 *
358 * This needs to be called at least once before any of the inode's data
359 * can be verified (and thus read at all) or the inode's fsverity digest
360 * retrieved. fsverity_file_open() calls this already, which handles
361 * normal file accesses. If a filesystem does any internal (i.e. not
362 * associated with a file descriptor) reads of the file's data or
363 * fsverity digest, it must call this explicitly before doing so.
364 *
365 * In case filesystem supports both fscrypt and fsverity, this should be called
366 * after fscrypt's encryption key is set up. Otherwise, the fsverity metadata is
367 * still encrypted. See fscrypt_file_open().
368 *
369 * Return: 0 on success, -errno on failure
370 */
371int fsverity_ensure_verity_info(struct inode *inode)
372{
373 struct fsverity_info *vi = fsverity_get_info(inode), *found;
374 struct fsverity_descriptor *desc;
375 int err;
376
377 if (vi)
378 return 0;
379
380 err = fsverity_get_descriptor(inode, &desc);
381 if (err)
382 return err;
383
384 vi = fsverity_create_info(inode, desc);
385 if (IS_ERR(vi)) {
386 err = PTR_ERR(vi);
387 goto out_free_desc;
388 }
389
390 /*
391 * Multiple tasks may race to set the inode's verity info, in which case
392 * we might find an existing fsverity_info in the hash table.
393 */
394 found = rhashtable_lookup_get_insert_fast(&fsverity_info_hash,
395 &vi->rhash_head,
396 fsverity_info_hash_params);
397 if (found) {
398 fsverity_free_info(vi);
399 if (IS_ERR(found))
400 err = PTR_ERR(found);
401 }
402
403out_free_desc:
404 kfree(desc);
405 return err;
406}
407EXPORT_SYMBOL_GPL(fsverity_ensure_verity_info);
408
409int __fsverity_file_open(struct inode *inode, struct file *filp)
410{
411 if (filp->f_mode & FMODE_WRITE)
412 return -EPERM;
413 return fsverity_ensure_verity_info(inode);
414}
415EXPORT_SYMBOL_GPL(__fsverity_file_open);
416
417void fsverity_free_info(struct fsverity_info *vi)
418{
419 kfree(vi->tree_params.hashstate);
420 kvfree(vi->hash_block_verified);
421 kmem_cache_free(fsverity_info_cachep, vi);
422}
423
424static void fsverity_free_info_rcu(struct rcu_head *head)
425{
426 fsverity_free_info(container_of(head, struct fsverity_info, rcu_head));
427}
428
429void fsverity_remove_info(struct fsverity_info *vi)
430{
431 rhashtable_remove_fast(&fsverity_info_hash, &vi->rhash_head,
432 fsverity_info_hash_params);
433 /*
434 * The freeing must be RCU-delayed because __fsverity_get_info() for a
435 * *different* inode's fsverity_info in the same rhashtable hash chain
436 * can still be accessing *this* fsverity_info's rhash_head and inode
437 * fields as part of the RCU-protected hash chain search.
438 */
439 call_rcu(&vi->rcu_head, fsverity_free_info_rcu);
440}
441
442void fsverity_cleanup_inode(struct inode *inode)
443{
444 struct fsverity_info *vi = fsverity_get_info(inode);
445
446 if (vi)
447 fsverity_remove_info(vi);
448}
449
450void __init fsverity_init_info_cache(void)
451{
452 if (rhashtable_init(&fsverity_info_hash, &fsverity_info_hash_params))
453 panic("failed to initialize fsverity hash\n");
454 fsverity_info_cachep = KMEM_CACHE_USERCOPY(
455 fsverity_info,
456 SLAB_RECLAIM_ACCOUNT | SLAB_PANIC,
457 file_digest);
458}