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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
13static struct workqueue_struct *fsverity_read_workqueue;
14
15/*
16 * Returns true if the hash block with index @hblock_idx in the tree, located in
17 * @hpage, has already been verified.
18 */
19static bool is_hash_block_verified(struct fsverity_info *vi, struct page *hpage,
20 unsigned long hblock_idx)
21{
22 bool verified;
23 unsigned int blocks_per_page;
24 unsigned int i;
25
26 /*
27 * When the Merkle tree block size and page size are the same, then the
28 * ->hash_block_verified bitmap isn't allocated, and we use PG_checked
29 * to directly indicate whether the page's block has been verified.
30 *
31 * Using PG_checked also guarantees that we re-verify hash pages that
32 * get evicted and re-instantiated from the backing storage, as new
33 * pages always start out with PG_checked cleared.
34 */
35 if (!vi->hash_block_verified)
36 return PageChecked(hpage);
37
38 /*
39 * When the Merkle tree block size and page size differ, we use a bitmap
40 * to indicate whether each hash block has been verified.
41 *
42 * However, we still need to ensure that hash pages that get evicted and
43 * re-instantiated from the backing storage are re-verified. To do
44 * this, we use PG_checked again, but now it doesn't really mean
45 * "checked". Instead, now it just serves as an indicator for whether
46 * the hash page is newly instantiated or not.
47 *
48 * The first thread that sees PG_checked=0 must clear the corresponding
49 * bitmap bits, then set PG_checked=1. This requires a spinlock. To
50 * avoid having to take this spinlock in the common case of
51 * PG_checked=1, we start with an opportunistic lockless read.
52 */
53 if (PageChecked(hpage)) {
54 /*
55 * A read memory barrier is needed here to give ACQUIRE
56 * semantics to the above PageChecked() test.
57 */
58 smp_rmb();
59 return test_bit(hblock_idx, vi->hash_block_verified);
60 }
61 spin_lock(&vi->hash_page_init_lock);
62 if (PageChecked(hpage)) {
63 verified = test_bit(hblock_idx, vi->hash_block_verified);
64 } else {
65 blocks_per_page = vi->tree_params.blocks_per_page;
66 hblock_idx = round_down(hblock_idx, blocks_per_page);
67 for (i = 0; i < blocks_per_page; i++)
68 clear_bit(hblock_idx + i, vi->hash_block_verified);
69 /*
70 * A write memory barrier is needed here to give RELEASE
71 * semantics to the below SetPageChecked() operation.
72 */
73 smp_wmb();
74 SetPageChecked(hpage);
75 verified = false;
76 }
77 spin_unlock(&vi->hash_page_init_lock);
78 return verified;
79}
80
81/*
82 * Verify a single data block against the file's Merkle tree.
83 *
84 * In principle, we need to verify the entire path to the root node. However,
85 * for efficiency the filesystem may cache the hash blocks. Therefore we need
86 * only ascend the tree until an already-verified hash block is seen, and then
87 * verify the path to that block.
88 *
89 * Return: %true if the data block is valid, else %false.
90 */
91static bool
92verify_data_block(struct inode *inode, struct fsverity_info *vi,
93 const void *data, u64 data_pos, unsigned long max_ra_pages)
94{
95 const struct merkle_tree_params *params = &vi->tree_params;
96 const unsigned int hsize = params->digest_size;
97 int level;
98 u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE];
99 const u8 *want_hash;
100 u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE];
101 /* The hash blocks that are traversed, indexed by level */
102 struct {
103 /* Page containing the hash block */
104 struct page *page;
105 /* Mapped address of the hash block (will be within @page) */
106 const void *addr;
107 /* Index of the hash block in the tree overall */
108 unsigned long index;
109 /* Byte offset of the wanted hash relative to @addr */
110 unsigned int hoffset;
111 } hblocks[FS_VERITY_MAX_LEVELS];
112 /*
113 * The index of the previous level's block within that level; also the
114 * index of that block's hash within the current level.
115 */
116 u64 hidx = data_pos >> params->log_blocksize;
117
118 /* Up to 1 + FS_VERITY_MAX_LEVELS pages may be mapped at once */
119 BUILD_BUG_ON(1 + FS_VERITY_MAX_LEVELS > KM_MAX_IDX);
120
121 if (unlikely(data_pos >= inode->i_size)) {
122 /*
123 * This can happen in the data page spanning EOF when the Merkle
124 * tree block size is less than the page size. The Merkle tree
125 * doesn't cover data blocks fully past EOF. But the entire
126 * page spanning EOF can be visible to userspace via a mmap, and
127 * any part past EOF should be all zeroes. Therefore, we need
128 * to verify that any data blocks fully past EOF are all zeroes.
129 */
130 if (memchr_inv(data, 0, params->block_size)) {
131 fsverity_err(inode,
132 "FILE CORRUPTED! Data past EOF is not zeroed");
133 return false;
134 }
135 return true;
136 }
137
138 /*
139 * Starting at the leaf level, ascend the tree saving hash blocks along
140 * the way until we find a hash block that has already been verified, or
141 * until we reach the root.
142 */
143 for (level = 0; level < params->num_levels; level++) {
144 unsigned long next_hidx;
145 unsigned long hblock_idx;
146 pgoff_t hpage_idx;
147 unsigned int hblock_offset_in_page;
148 unsigned int hoffset;
149 struct page *hpage;
150 const void *haddr;
151
152 /*
153 * The index of the block in the current level; also the index
154 * of that block's hash within the next level.
155 */
156 next_hidx = hidx >> params->log_arity;
157
158 /* Index of the hash block in the tree overall */
159 hblock_idx = params->level_start[level] + next_hidx;
160
161 /* Index of the hash page in the tree overall */
162 hpage_idx = hblock_idx >> params->log_blocks_per_page;
163
164 /* Byte offset of the hash block within the page */
165 hblock_offset_in_page =
166 (hblock_idx << params->log_blocksize) & ~PAGE_MASK;
167
168 /* Byte offset of the hash within the block */
169 hoffset = (hidx << params->log_digestsize) &
170 (params->block_size - 1);
171
172 hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode,
173 hpage_idx, level == 0 ? min(max_ra_pages,
174 params->tree_pages - hpage_idx) : 0);
175 if (IS_ERR(hpage)) {
176 fsverity_err(inode,
177 "Error %ld reading Merkle tree page %lu",
178 PTR_ERR(hpage), hpage_idx);
179 goto error;
180 }
181 haddr = kmap_local_page(hpage) + hblock_offset_in_page;
182 if (is_hash_block_verified(vi, hpage, hblock_idx)) {
183 memcpy(_want_hash, haddr + hoffset, hsize);
184 want_hash = _want_hash;
185 kunmap_local(haddr);
186 put_page(hpage);
187 goto descend;
188 }
189 hblocks[level].page = hpage;
190 hblocks[level].addr = haddr;
191 hblocks[level].index = hblock_idx;
192 hblocks[level].hoffset = hoffset;
193 hidx = next_hidx;
194 }
195
196 want_hash = vi->root_hash;
197descend:
198 /* Descend the tree verifying hash blocks. */
199 for (; level > 0; level--) {
200 struct page *hpage = hblocks[level - 1].page;
201 const void *haddr = hblocks[level - 1].addr;
202 unsigned long hblock_idx = hblocks[level - 1].index;
203 unsigned int hoffset = hblocks[level - 1].hoffset;
204
205 if (fsverity_hash_block(params, inode, haddr, real_hash) != 0)
206 goto error;
207 if (memcmp(want_hash, real_hash, hsize) != 0)
208 goto corrupted;
209 /*
210 * Mark the hash block as verified. This must be atomic and
211 * idempotent, as the same hash block might be verified by
212 * multiple threads concurrently.
213 */
214 if (vi->hash_block_verified)
215 set_bit(hblock_idx, vi->hash_block_verified);
216 else
217 SetPageChecked(hpage);
218 memcpy(_want_hash, haddr + hoffset, hsize);
219 want_hash = _want_hash;
220 kunmap_local(haddr);
221 put_page(hpage);
222 }
223
224 /* Finally, verify the data block. */
225 if (fsverity_hash_block(params, inode, data, real_hash) != 0)
226 goto error;
227 if (memcmp(want_hash, real_hash, hsize) != 0)
228 goto corrupted;
229 return true;
230
231corrupted:
232 fsverity_err(inode,
233 "FILE CORRUPTED! pos=%llu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN",
234 data_pos, level - 1,
235 params->hash_alg->name, hsize, want_hash,
236 params->hash_alg->name, hsize, real_hash);
237error:
238 for (; level > 0; level--) {
239 kunmap_local(hblocks[level - 1].addr);
240 put_page(hblocks[level - 1].page);
241 }
242 return false;
243}
244
245static bool
246verify_data_blocks(struct folio *data_folio, size_t len, size_t offset,
247 unsigned long max_ra_pages)
248{
249 struct inode *inode = data_folio->mapping->host;
250 struct fsverity_info *vi = inode->i_verity_info;
251 const unsigned int block_size = vi->tree_params.block_size;
252 u64 pos = (u64)data_folio->index << PAGE_SHIFT;
253
254 if (WARN_ON_ONCE(len <= 0 || !IS_ALIGNED(len | offset, block_size)))
255 return false;
256 if (WARN_ON_ONCE(!folio_test_locked(data_folio) ||
257 folio_test_uptodate(data_folio)))
258 return false;
259 do {
260 void *data;
261 bool valid;
262
263 data = kmap_local_folio(data_folio, offset);
264 valid = verify_data_block(inode, vi, data, pos + offset,
265 max_ra_pages);
266 kunmap_local(data);
267 if (!valid)
268 return false;
269 offset += block_size;
270 len -= block_size;
271 } while (len);
272 return true;
273}
274
275/**
276 * fsverity_verify_blocks() - verify data in a folio
277 * @folio: the folio containing the data to verify
278 * @len: the length of the data to verify in the folio
279 * @offset: the offset of the data to verify in the folio
280 *
281 * Verify data that has just been read from a verity file. The data must be
282 * located in a pagecache folio that is still locked and not yet uptodate. The
283 * length and offset of the data must be Merkle tree block size aligned.
284 *
285 * Return: %true if the data is valid, else %false.
286 */
287bool fsverity_verify_blocks(struct folio *folio, size_t len, size_t offset)
288{
289 return verify_data_blocks(folio, len, offset, 0);
290}
291EXPORT_SYMBOL_GPL(fsverity_verify_blocks);
292
293#ifdef CONFIG_BLOCK
294/**
295 * fsverity_verify_bio() - verify a 'read' bio that has just completed
296 * @bio: the bio to verify
297 *
298 * Verify the bio's data against the file's Merkle tree. All bio data segments
299 * must be aligned to the file's Merkle tree block size. If any data fails
300 * verification, then bio->bi_status is set to an error status.
301 *
302 * This is a helper function for use by the ->readahead() method of filesystems
303 * that issue bios to read data directly into the page cache. Filesystems that
304 * populate the page cache without issuing bios (e.g. non block-based
305 * filesystems) must instead call fsverity_verify_page() directly on each page.
306 * All filesystems must also call fsverity_verify_page() on holes.
307 */
308void fsverity_verify_bio(struct bio *bio)
309{
310 struct folio_iter fi;
311 unsigned long max_ra_pages = 0;
312
313 if (bio->bi_opf & REQ_RAHEAD) {
314 /*
315 * If this bio is for data readahead, then we also do readahead
316 * of the first (largest) level of the Merkle tree. Namely,
317 * when a Merkle tree page is read, we also try to piggy-back on
318 * some additional pages -- up to 1/4 the number of data pages.
319 *
320 * This improves sequential read performance, as it greatly
321 * reduces the number of I/O requests made to the Merkle tree.
322 */
323 max_ra_pages = bio->bi_iter.bi_size >> (PAGE_SHIFT + 2);
324 }
325
326 bio_for_each_folio_all(fi, bio) {
327 if (!verify_data_blocks(fi.folio, fi.length, fi.offset,
328 max_ra_pages)) {
329 bio->bi_status = BLK_STS_IOERR;
330 break;
331 }
332 }
333}
334EXPORT_SYMBOL_GPL(fsverity_verify_bio);
335#endif /* CONFIG_BLOCK */
336
337/**
338 * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue
339 * @work: the work to enqueue
340 *
341 * Enqueue verification work for asynchronous processing.
342 */
343void fsverity_enqueue_verify_work(struct work_struct *work)
344{
345 queue_work(fsverity_read_workqueue, work);
346}
347EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work);
348
349void __init fsverity_init_workqueue(void)
350{
351 /*
352 * Use a high-priority workqueue to prioritize verification work, which
353 * blocks reads from completing, over regular application tasks.
354 *
355 * For performance reasons, don't use an unbound workqueue. Using an
356 * unbound workqueue for crypto operations causes excessive scheduler
357 * latency on ARM64.
358 */
359 fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue",
360 WQ_HIGHPRI,
361 num_online_cpus());
362 if (!fsverity_read_workqueue)
363 panic("failed to allocate fsverity_read_queue");
364}
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}