Loading...
Note: File does not exist in v4.17.
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Data verification functions, i.e. hooks for ->readahead()
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
14static 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 */
25static 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
42static inline int cmp_hashes(const struct fsverity_info *vi,
43 const u8 *want_hash, const u8 *real_hash,
44 pgoff_t index, int level)
45{
46 const unsigned int hsize = vi->tree_params.digest_size;
47
48 if (memcmp(want_hash, real_hash, hsize) == 0)
49 return 0;
50
51 fsverity_err(vi->inode,
52 "FILE CORRUPTED! index=%lu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN",
53 index, level,
54 vi->tree_params.hash_alg->name, hsize, want_hash,
55 vi->tree_params.hash_alg->name, hsize, real_hash);
56 return -EBADMSG;
57}
58
59/*
60 * Verify a single data page against the file's Merkle tree.
61 *
62 * In principle, we need to verify the entire path to the root node. However,
63 * for efficiency the filesystem may cache the hash pages. Therefore we need
64 * only ascend the tree until an already-verified page is seen, as indicated by
65 * the PageChecked bit being set; then verify the path to that page.
66 *
67 * This code currently only supports the case where the verity block size is
68 * equal to PAGE_SIZE. Doing otherwise would be possible but tricky, since we
69 * wouldn't be able to use the PageChecked bit.
70 *
71 * Note that multiple processes may race to verify a hash page and mark it
72 * Checked, but it doesn't matter; the result will be the same either way.
73 *
74 * Return: true if the page is valid, else false.
75 */
76static bool verify_page(struct inode *inode, const struct fsverity_info *vi,
77 struct ahash_request *req, struct page *data_page,
78 unsigned long level0_ra_pages)
79{
80 const struct merkle_tree_params *params = &vi->tree_params;
81 const unsigned int hsize = params->digest_size;
82 const pgoff_t index = data_page->index;
83 int level;
84 u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE];
85 const u8 *want_hash;
86 u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE];
87 struct page *hpages[FS_VERITY_MAX_LEVELS];
88 unsigned int hoffsets[FS_VERITY_MAX_LEVELS];
89 int err;
90
91 if (WARN_ON_ONCE(!PageLocked(data_page) || PageUptodate(data_page)))
92 return false;
93
94 pr_debug_ratelimited("Verifying data page %lu...\n", index);
95
96 /*
97 * Starting at the leaf level, ascend the tree saving hash pages along
98 * the way until we find a verified hash page, indicated by PageChecked;
99 * or until we reach the root.
100 */
101 for (level = 0; level < params->num_levels; level++) {
102 pgoff_t hindex;
103 unsigned int hoffset;
104 struct page *hpage;
105
106 hash_at_level(params, index, level, &hindex, &hoffset);
107
108 pr_debug_ratelimited("Level %d: hindex=%lu, hoffset=%u\n",
109 level, hindex, hoffset);
110
111 hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode, hindex,
112 level == 0 ? level0_ra_pages : 0);
113 if (IS_ERR(hpage)) {
114 err = PTR_ERR(hpage);
115 fsverity_err(inode,
116 "Error %d reading Merkle tree page %lu",
117 err, hindex);
118 goto out;
119 }
120
121 if (PageChecked(hpage)) {
122 memcpy_from_page(_want_hash, hpage, hoffset, hsize);
123 want_hash = _want_hash;
124 put_page(hpage);
125 pr_debug_ratelimited("Hash page already checked, want %s:%*phN\n",
126 params->hash_alg->name,
127 hsize, want_hash);
128 goto descend;
129 }
130 pr_debug_ratelimited("Hash page not yet checked\n");
131 hpages[level] = hpage;
132 hoffsets[level] = hoffset;
133 }
134
135 want_hash = vi->root_hash;
136 pr_debug("Want root hash: %s:%*phN\n",
137 params->hash_alg->name, hsize, want_hash);
138descend:
139 /* Descend the tree verifying hash pages */
140 for (; level > 0; level--) {
141 struct page *hpage = hpages[level - 1];
142 unsigned int hoffset = hoffsets[level - 1];
143
144 err = fsverity_hash_page(params, inode, req, hpage, real_hash);
145 if (err)
146 goto out;
147 err = cmp_hashes(vi, want_hash, real_hash, index, level - 1);
148 if (err)
149 goto out;
150 SetPageChecked(hpage);
151 memcpy_from_page(_want_hash, hpage, hoffset, hsize);
152 want_hash = _want_hash;
153 put_page(hpage);
154 pr_debug("Verified hash page at level %d, now want %s:%*phN\n",
155 level - 1, params->hash_alg->name, hsize, want_hash);
156 }
157
158 /* Finally, verify the data page */
159 err = fsverity_hash_page(params, inode, req, data_page, real_hash);
160 if (err)
161 goto out;
162 err = cmp_hashes(vi, want_hash, real_hash, index, -1);
163out:
164 for (; level > 0; level--)
165 put_page(hpages[level - 1]);
166
167 return err == 0;
168}
169
170/**
171 * fsverity_verify_page() - verify a data page
172 * @page: the page to verity
173 *
174 * Verify a page that has just been read from a verity file. The page must be a
175 * pagecache page that is still locked and not yet uptodate.
176 *
177 * Return: true if the page is valid, else false.
178 */
179bool fsverity_verify_page(struct page *page)
180{
181 struct inode *inode = page->mapping->host;
182 const struct fsverity_info *vi = inode->i_verity_info;
183 struct ahash_request *req;
184 bool valid;
185
186 /* This allocation never fails, since it's mempool-backed. */
187 req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS);
188
189 valid = verify_page(inode, vi, req, page, 0);
190
191 fsverity_free_hash_request(vi->tree_params.hash_alg, req);
192
193 return valid;
194}
195EXPORT_SYMBOL_GPL(fsverity_verify_page);
196
197#ifdef CONFIG_BLOCK
198/**
199 * fsverity_verify_bio() - verify a 'read' bio that has just completed
200 * @bio: the bio to verify
201 *
202 * Verify a set of pages that have just been read from a verity file. The pages
203 * must be pagecache pages that are still locked and not yet uptodate. If a
204 * page fails verification, then bio->bi_status is set to an error status.
205 *
206 * This is a helper function for use by the ->readahead() method of filesystems
207 * that issue bios to read data directly into the page cache. Filesystems that
208 * populate the page cache without issuing bios (e.g. non block-based
209 * filesystems) must instead call fsverity_verify_page() directly on each page.
210 * All filesystems must also call fsverity_verify_page() on holes.
211 */
212void fsverity_verify_bio(struct bio *bio)
213{
214 struct inode *inode = bio_first_page_all(bio)->mapping->host;
215 const struct fsverity_info *vi = inode->i_verity_info;
216 const struct merkle_tree_params *params = &vi->tree_params;
217 struct ahash_request *req;
218 struct bio_vec *bv;
219 struct bvec_iter_all iter_all;
220 unsigned long max_ra_pages = 0;
221
222 /* This allocation never fails, since it's mempool-backed. */
223 req = fsverity_alloc_hash_request(params->hash_alg, GFP_NOFS);
224
225 if (bio->bi_opf & REQ_RAHEAD) {
226 /*
227 * If this bio is for data readahead, then we also do readahead
228 * of the first (largest) level of the Merkle tree. Namely,
229 * when a Merkle tree page is read, we also try to piggy-back on
230 * some additional pages -- up to 1/4 the number of data pages.
231 *
232 * This improves sequential read performance, as it greatly
233 * reduces the number of I/O requests made to the Merkle tree.
234 */
235 bio_for_each_segment_all(bv, bio, iter_all)
236 max_ra_pages++;
237 max_ra_pages /= 4;
238 }
239
240 bio_for_each_segment_all(bv, bio, iter_all) {
241 struct page *page = bv->bv_page;
242 unsigned long level0_index = page->index >> params->log_arity;
243 unsigned long level0_ra_pages =
244 min(max_ra_pages, params->level0_blocks - level0_index);
245
246 if (!verify_page(inode, vi, req, page, level0_ra_pages)) {
247 bio->bi_status = BLK_STS_IOERR;
248 break;
249 }
250 }
251
252 fsverity_free_hash_request(params->hash_alg, req);
253}
254EXPORT_SYMBOL_GPL(fsverity_verify_bio);
255#endif /* CONFIG_BLOCK */
256
257/**
258 * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue
259 * @work: the work to enqueue
260 *
261 * Enqueue verification work for asynchronous processing.
262 */
263void fsverity_enqueue_verify_work(struct work_struct *work)
264{
265 queue_work(fsverity_read_workqueue, work);
266}
267EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work);
268
269int __init fsverity_init_workqueue(void)
270{
271 /*
272 * Use an unbound workqueue to allow bios to be verified in parallel
273 * even when they happen to complete on the same CPU. This sacrifices
274 * locality, but it's worthwhile since hashing is CPU-intensive.
275 *
276 * Also use a high-priority workqueue to prioritize verification work,
277 * which blocks reads from completing, over regular application tasks.
278 */
279 fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue",
280 WQ_UNBOUND | WQ_HIGHPRI,
281 num_online_cpus());
282 if (!fsverity_read_workqueue)
283 return -ENOMEM;
284 return 0;
285}
286
287void __init fsverity_exit_workqueue(void)
288{
289 destroy_workqueue(fsverity_read_workqueue);
290 fsverity_read_workqueue = NULL;
291}