1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Data verification functions, i.e. hooks for ->readpages()
4 *
5 * Copyright 2019 Google LLC
6 */
7
8 #include "fsverity_private.h"
9
10 #include <crypto/hash.h>
11 #include <linux/bio.h>
12 #include <linux/ratelimit.h>
13
14 static struct workqueue_struct *fsverity_read_workqueue;
15
16 /**
17 * hash_at_level() - compute the location of the block's hash at the given level
18 *
19 * @params: (in) the Merkle tree parameters
20 * @dindex: (in) the index of the data block being verified
21 * @level: (in) the level of hash we want (0 is leaf level)
22 * @hindex: (out) the index of the hash block containing the wanted hash
23 * @hoffset: (out) the byte offset to the wanted hash within the hash block
24 */
hash_at_level(const struct merkle_tree_params * params,pgoff_t dindex,unsigned int level,pgoff_t * hindex,unsigned int * hoffset)25 static void hash_at_level(const struct merkle_tree_params *params,
26 pgoff_t dindex, unsigned int level, pgoff_t *hindex,
27 unsigned int *hoffset)
28 {
29 pgoff_t position;
30
31 /* Offset of the hash within the level's region, in hashes */
32 position = dindex >> (level * params->log_arity);
33
34 /* Index of the hash block in the tree overall */
35 *hindex = params->level_start[level] + (position >> params->log_arity);
36
37 /* Offset of the wanted hash (in bytes) within the hash block */
38 *hoffset = (position & ((1 << params->log_arity) - 1)) <<
39 (params->log_blocksize - params->log_arity);
40 }
41
42 /* Extract a hash from a hash page */
extract_hash(struct page * hpage,unsigned int hoffset,unsigned int hsize,u8 * out)43 static void extract_hash(struct page *hpage, unsigned int hoffset,
44 unsigned int hsize, u8 *out)
45 {
46 void *virt = kmap_atomic(hpage);
47
48 memcpy(out, virt + hoffset, hsize);
49 kunmap_atomic(virt);
50 }
51
cmp_hashes(const struct fsverity_info * vi,const u8 * want_hash,const u8 * real_hash,pgoff_t index,int level)52 static inline int cmp_hashes(const struct fsverity_info *vi,
53 const u8 *want_hash, const u8 *real_hash,
54 pgoff_t index, int level)
55 {
56 const unsigned int hsize = vi->tree_params.digest_size;
57
58 if (memcmp(want_hash, real_hash, hsize) == 0)
59 return 0;
60
61 fsverity_err(vi->inode,
62 "FILE CORRUPTED! index=%lu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN",
63 index, level,
64 vi->tree_params.hash_alg->name, hsize, want_hash,
65 vi->tree_params.hash_alg->name, hsize, real_hash);
66 return -EBADMSG;
67 }
68
69 /*
70 * Verify a single data page against the file's Merkle tree.
71 *
72 * In principle, we need to verify the entire path to the root node. However,
73 * for efficiency the filesystem may cache the hash pages. Therefore we need
74 * only ascend the tree until an already-verified page is seen, as indicated by
75 * the PageChecked bit being set; then verify the path to that page.
76 *
77 * This code currently only supports the case where the verity block size is
78 * equal to PAGE_SIZE. Doing otherwise would be possible but tricky, since we
79 * wouldn't be able to use the PageChecked bit.
80 *
81 * Note that multiple processes may race to verify a hash page and mark it
82 * Checked, but it doesn't matter; the result will be the same either way.
83 *
84 * Return: true if the page is valid, else false.
85 */
verify_page(struct inode * inode,const struct fsverity_info * vi,struct ahash_request * req,struct page * data_page,unsigned long level0_ra_pages)86 static bool verify_page(struct inode *inode, const struct fsverity_info *vi,
87 struct ahash_request *req, struct page *data_page,
88 unsigned long level0_ra_pages)
89 {
90 const struct merkle_tree_params *params = &vi->tree_params;
91 const unsigned int hsize = params->digest_size;
92 const pgoff_t index = data_page->index;
93 int level;
94 u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE];
95 const u8 *want_hash;
96 u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE];
97 struct page *hpages[FS_VERITY_MAX_LEVELS];
98 unsigned int hoffsets[FS_VERITY_MAX_LEVELS];
99 int err;
100
101 if (WARN_ON_ONCE(!PageLocked(data_page) || PageUptodate(data_page)))
102 return false;
103
104 pr_debug_ratelimited("Verifying data page %lu...\n", index);
105
106 /*
107 * Starting at the leaf level, ascend the tree saving hash pages along
108 * the way until we find a verified hash page, indicated by PageChecked;
109 * or until we reach the root.
110 */
111 for (level = 0; level < params->num_levels; level++) {
112 pgoff_t hindex;
113 unsigned int hoffset;
114 struct page *hpage;
115
116 hash_at_level(params, index, level, &hindex, &hoffset);
117
118 pr_debug_ratelimited("Level %d: hindex=%lu, hoffset=%u\n",
119 level, hindex, hoffset);
120
121 hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode, hindex,
122 level == 0 ? level0_ra_pages : 0);
123 if (IS_ERR(hpage)) {
124 err = PTR_ERR(hpage);
125 fsverity_err(inode,
126 "Error %d reading Merkle tree page %lu",
127 err, hindex);
128 goto out;
129 }
130
131 if (PageChecked(hpage)) {
132 extract_hash(hpage, hoffset, hsize, _want_hash);
133 want_hash = _want_hash;
134 put_page(hpage);
135 pr_debug_ratelimited("Hash page already checked, want %s:%*phN\n",
136 params->hash_alg->name,
137 hsize, want_hash);
138 goto descend;
139 }
140 pr_debug_ratelimited("Hash page not yet checked\n");
141 hpages[level] = hpage;
142 hoffsets[level] = hoffset;
143 }
144
145 want_hash = vi->root_hash;
146 pr_debug("Want root hash: %s:%*phN\n",
147 params->hash_alg->name, hsize, want_hash);
148 descend:
149 /* Descend the tree verifying hash pages */
150 for (; level > 0; level--) {
151 struct page *hpage = hpages[level - 1];
152 unsigned int hoffset = hoffsets[level - 1];
153
154 err = fsverity_hash_page(params, inode, req, hpage, real_hash);
155 if (err)
156 goto out;
157 err = cmp_hashes(vi, want_hash, real_hash, index, level - 1);
158 if (err)
159 goto out;
160 SetPageChecked(hpage);
161 extract_hash(hpage, hoffset, hsize, _want_hash);
162 want_hash = _want_hash;
163 put_page(hpage);
164 pr_debug("Verified hash page at level %d, now want %s:%*phN\n",
165 level - 1, params->hash_alg->name, hsize, want_hash);
166 }
167
168 /* Finally, verify the data page */
169 err = fsverity_hash_page(params, inode, req, data_page, real_hash);
170 if (err)
171 goto out;
172 err = cmp_hashes(vi, want_hash, real_hash, index, -1);
173 out:
174 for (; level > 0; level--)
175 put_page(hpages[level - 1]);
176
177 return err == 0;
178 }
179
180 /**
181 * fsverity_verify_page() - verify a data page
182 * @page: the page to verity
183 *
184 * Verify a page that has just been read from a verity file. The page must be a
185 * pagecache page that is still locked and not yet uptodate.
186 *
187 * Return: true if the page is valid, else false.
188 */
fsverity_verify_page(struct page * page)189 bool fsverity_verify_page(struct page *page)
190 {
191 struct inode *inode = page->mapping->host;
192 const struct fsverity_info *vi = inode->i_verity_info;
193 struct ahash_request *req;
194 bool valid;
195
196 /* This allocation never fails, since it's mempool-backed. */
197 req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS);
198
199 valid = verify_page(inode, vi, req, page, 0);
200
201 fsverity_free_hash_request(vi->tree_params.hash_alg, req);
202
203 return valid;
204 }
205 EXPORT_SYMBOL_GPL(fsverity_verify_page);
206
207 #ifdef CONFIG_BLOCK
208 /**
209 * fsverity_verify_bio() - verify a 'read' bio that has just completed
210 * @bio: the bio to verify
211 *
212 * Verify a set of pages that have just been read from a verity file. The pages
213 * must be pagecache pages that are still locked and not yet uptodate. Pages
214 * that fail verification are set to the Error state. Verification is skipped
215 * for pages already in the Error state, e.g. due to fscrypt decryption failure.
216 *
217 * This is a helper function for use by the ->readpages() method of filesystems
218 * that issue bios to read data directly into the page cache. Filesystems that
219 * populate the page cache without issuing bios (e.g. non block-based
220 * filesystems) must instead call fsverity_verify_page() directly on each page.
221 * All filesystems must also call fsverity_verify_page() on holes.
222 */
fsverity_verify_bio(struct bio * bio)223 void fsverity_verify_bio(struct bio *bio)
224 {
225 struct inode *inode = bio_first_page_all(bio)->mapping->host;
226 const struct fsverity_info *vi = inode->i_verity_info;
227 const struct merkle_tree_params *params = &vi->tree_params;
228 struct ahash_request *req;
229 struct bio_vec *bv;
230 struct bvec_iter_all iter_all;
231 unsigned long max_ra_pages = 0;
232
233 /* This allocation never fails, since it's mempool-backed. */
234 req = fsverity_alloc_hash_request(params->hash_alg, GFP_NOFS);
235
236 if (bio->bi_opf & REQ_RAHEAD) {
237 /*
238 * If this bio is for data readahead, then we also do readahead
239 * of the first (largest) level of the Merkle tree. Namely,
240 * when a Merkle tree page is read, we also try to piggy-back on
241 * some additional pages -- up to 1/4 the number of data pages.
242 *
243 * This improves sequential read performance, as it greatly
244 * reduces the number of I/O requests made to the Merkle tree.
245 */
246 bio_for_each_segment_all(bv, bio, iter_all)
247 max_ra_pages++;
248 max_ra_pages /= 4;
249 }
250
251 bio_for_each_segment_all(bv, bio, iter_all) {
252 struct page *page = bv->bv_page;
253 unsigned long level0_index = page->index >> params->log_arity;
254 unsigned long level0_ra_pages =
255 min(max_ra_pages, params->level0_blocks - level0_index);
256
257 if (!PageError(page) &&
258 !verify_page(inode, vi, req, page, level0_ra_pages))
259 SetPageError(page);
260 }
261
262 fsverity_free_hash_request(params->hash_alg, req);
263 }
264 EXPORT_SYMBOL_GPL(fsverity_verify_bio);
265 #endif /* CONFIG_BLOCK */
266
267 /**
268 * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue
269 * @work: the work to enqueue
270 *
271 * Enqueue verification work for asynchronous processing.
272 */
fsverity_enqueue_verify_work(struct work_struct * work)273 void fsverity_enqueue_verify_work(struct work_struct *work)
274 {
275 queue_work(fsverity_read_workqueue, work);
276 }
277 EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work);
278
fsverity_init_workqueue(void)279 int __init fsverity_init_workqueue(void)
280 {
281 /*
282 * Use a high-priority workqueue to prioritize verification work, which
283 * blocks reads from completing, over regular application tasks.
284 *
285 * For performance reasons, don't use an unbound workqueue. Using an
286 * unbound workqueue for crypto operations causes excessive scheduler
287 * latency on ARM64.
288 */
289 fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue",
290 WQ_HIGHPRI,
291 num_online_cpus());
292 if (!fsverity_read_workqueue)
293 return -ENOMEM;
294 return 0;
295 }
296
fsverity_exit_workqueue(void)297 void __init fsverity_exit_workqueue(void)
298 {
299 destroy_workqueue(fsverity_read_workqueue);
300 fsverity_read_workqueue = NULL;
301 }
302