1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* |
3 | * fs/ext4/verity.c: fs-verity support for ext4 |
4 | * |
5 | * Copyright 2019 Google LLC |
6 | */ |
7 | |
8 | /* |
9 | * Implementation of fsverity_operations for ext4. |
10 | * |
11 | * ext4 stores the verity metadata (Merkle tree and fsverity_descriptor) past |
12 | * the end of the file, starting at the first 64K boundary beyond i_size. This |
13 | * approach works because (a) verity files are readonly, and (b) pages fully |
14 | * beyond i_size aren't visible to userspace but can be read/written internally |
15 | * by ext4 with only some relatively small changes to ext4. This approach |
16 | * avoids having to depend on the EA_INODE feature and on rearchitecturing |
17 | * ext4's xattr support to support paging multi-gigabyte xattrs into memory, and |
18 | * to support encrypting xattrs. Note that the verity metadata *must* be |
19 | * encrypted when the file is, since it contains hashes of the plaintext data. |
20 | * |
21 | * Using a 64K boundary rather than a 4K one keeps things ready for |
22 | * architectures with 64K pages, and it doesn't necessarily waste space on-disk |
23 | * since there can be a hole between i_size and the start of the Merkle tree. |
24 | */ |
25 | |
26 | #include <linux/quotaops.h> |
27 | |
28 | #include "ext4.h" |
29 | #include "ext4_extents.h" |
30 | #include "ext4_jbd2.h" |
31 | |
32 | static inline loff_t ext4_verity_metadata_pos(const struct inode *inode) |
33 | { |
34 | return round_up(inode->i_size, 65536); |
35 | } |
36 | |
37 | /* |
38 | * Read some verity metadata from the inode. __vfs_read() can't be used because |
39 | * we need to read beyond i_size. |
40 | */ |
41 | static int pagecache_read(struct inode *inode, void *buf, size_t count, |
42 | loff_t pos) |
43 | { |
44 | while (count) { |
45 | struct folio *folio; |
46 | size_t n; |
47 | |
48 | folio = read_mapping_folio(mapping: inode->i_mapping, index: pos >> PAGE_SHIFT, |
49 | NULL); |
50 | if (IS_ERR(ptr: folio)) |
51 | return PTR_ERR(ptr: folio); |
52 | |
53 | n = memcpy_from_file_folio(to: buf, folio, pos, len: count); |
54 | folio_put(folio); |
55 | |
56 | buf += n; |
57 | pos += n; |
58 | count -= n; |
59 | } |
60 | return 0; |
61 | } |
62 | |
63 | /* |
64 | * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY. |
65 | * kernel_write() can't be used because the file descriptor is readonly. |
66 | */ |
67 | static int pagecache_write(struct inode *inode, const void *buf, size_t count, |
68 | loff_t pos) |
69 | { |
70 | struct address_space *mapping = inode->i_mapping; |
71 | const struct address_space_operations *aops = mapping->a_ops; |
72 | |
73 | if (pos + count > inode->i_sb->s_maxbytes) |
74 | return -EFBIG; |
75 | |
76 | while (count) { |
77 | size_t n = min_t(size_t, count, |
78 | PAGE_SIZE - offset_in_page(pos)); |
79 | struct page *page; |
80 | void *fsdata = NULL; |
81 | int res; |
82 | |
83 | res = aops->write_begin(NULL, mapping, pos, n, &page, &fsdata); |
84 | if (res) |
85 | return res; |
86 | |
87 | memcpy_to_page(page, offset_in_page(pos), from: buf, len: n); |
88 | |
89 | res = aops->write_end(NULL, mapping, pos, n, n, page, fsdata); |
90 | if (res < 0) |
91 | return res; |
92 | if (res != n) |
93 | return -EIO; |
94 | |
95 | buf += n; |
96 | pos += n; |
97 | count -= n; |
98 | } |
99 | return 0; |
100 | } |
101 | |
102 | static int ext4_begin_enable_verity(struct file *filp) |
103 | { |
104 | struct inode *inode = file_inode(f: filp); |
105 | const int credits = 2; /* superblock and inode for ext4_orphan_add() */ |
106 | handle_t *handle; |
107 | int err; |
108 | |
109 | if (IS_DAX(inode) || ext4_test_inode_flag(inode, bit: EXT4_INODE_DAX)) |
110 | return -EINVAL; |
111 | |
112 | if (ext4_verity_in_progress(inode)) |
113 | return -EBUSY; |
114 | |
115 | /* |
116 | * Since the file was opened readonly, we have to initialize the jbd |
117 | * inode and quotas here and not rely on ->open() doing it. This must |
118 | * be done before evicting the inline data. |
119 | */ |
120 | |
121 | err = ext4_inode_attach_jinode(inode); |
122 | if (err) |
123 | return err; |
124 | |
125 | err = dquot_initialize(inode); |
126 | if (err) |
127 | return err; |
128 | |
129 | err = ext4_convert_inline_data(inode); |
130 | if (err) |
131 | return err; |
132 | |
133 | if (!ext4_test_inode_flag(inode, bit: EXT4_INODE_EXTENTS)) { |
134 | ext4_warning_inode(inode, |
135 | "verity is only allowed on extent-based files" ); |
136 | return -EOPNOTSUPP; |
137 | } |
138 | |
139 | /* |
140 | * ext4 uses the last allocated block to find the verity descriptor, so |
141 | * we must remove any other blocks past EOF which might confuse things. |
142 | */ |
143 | err = ext4_truncate(inode); |
144 | if (err) |
145 | return err; |
146 | |
147 | handle = ext4_journal_start(inode, EXT4_HT_INODE, credits); |
148 | if (IS_ERR(ptr: handle)) |
149 | return PTR_ERR(ptr: handle); |
150 | |
151 | err = ext4_orphan_add(handle, inode); |
152 | if (err == 0) |
153 | ext4_set_inode_state(inode, bit: EXT4_STATE_VERITY_IN_PROGRESS); |
154 | |
155 | ext4_journal_stop(handle); |
156 | return err; |
157 | } |
158 | |
159 | /* |
160 | * ext4 stores the verity descriptor beginning on the next filesystem block |
161 | * boundary after the Merkle tree. Then, the descriptor size is stored in the |
162 | * last 4 bytes of the last allocated filesystem block --- which is either the |
163 | * block in which the descriptor ends, or the next block after that if there |
164 | * weren't at least 4 bytes remaining. |
165 | * |
166 | * We can't simply store the descriptor in an xattr because it *must* be |
167 | * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt |
168 | * xattrs. Also, if the descriptor includes a large signature blob it may be |
169 | * too large to store in an xattr without the EA_INODE feature. |
170 | */ |
171 | static int ext4_write_verity_descriptor(struct inode *inode, const void *desc, |
172 | size_t desc_size, u64 merkle_tree_size) |
173 | { |
174 | const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) + |
175 | merkle_tree_size, i_blocksize(inode)); |
176 | const u64 desc_end = desc_pos + desc_size; |
177 | const __le32 desc_size_disk = cpu_to_le32(desc_size); |
178 | const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk), |
179 | i_blocksize(inode)) - |
180 | sizeof(desc_size_disk); |
181 | int err; |
182 | |
183 | err = pagecache_write(inode, buf: desc, count: desc_size, pos: desc_pos); |
184 | if (err) |
185 | return err; |
186 | |
187 | return pagecache_write(inode, buf: &desc_size_disk, count: sizeof(desc_size_disk), |
188 | pos: desc_size_pos); |
189 | } |
190 | |
191 | static int ext4_end_enable_verity(struct file *filp, const void *desc, |
192 | size_t desc_size, u64 merkle_tree_size) |
193 | { |
194 | struct inode *inode = file_inode(f: filp); |
195 | const int credits = 2; /* superblock and inode for ext4_orphan_del() */ |
196 | handle_t *handle; |
197 | struct ext4_iloc iloc; |
198 | int err = 0; |
199 | |
200 | /* |
201 | * If an error already occurred (which fs/verity/ signals by passing |
202 | * desc == NULL), then only clean-up is needed. |
203 | */ |
204 | if (desc == NULL) |
205 | goto cleanup; |
206 | |
207 | /* Append the verity descriptor. */ |
208 | err = ext4_write_verity_descriptor(inode, desc, desc_size, |
209 | merkle_tree_size); |
210 | if (err) |
211 | goto cleanup; |
212 | |
213 | /* |
214 | * Write all pages (both data and verity metadata). Note that this must |
215 | * happen before clearing EXT4_STATE_VERITY_IN_PROGRESS; otherwise pages |
216 | * beyond i_size won't be written properly. For crash consistency, this |
217 | * also must happen before the verity inode flag gets persisted. |
218 | */ |
219 | err = filemap_write_and_wait(mapping: inode->i_mapping); |
220 | if (err) |
221 | goto cleanup; |
222 | |
223 | /* |
224 | * Finally, set the verity inode flag and remove the inode from the |
225 | * orphan list (in a single transaction). |
226 | */ |
227 | |
228 | handle = ext4_journal_start(inode, EXT4_HT_INODE, credits); |
229 | if (IS_ERR(ptr: handle)) { |
230 | err = PTR_ERR(ptr: handle); |
231 | goto cleanup; |
232 | } |
233 | |
234 | err = ext4_orphan_del(handle, inode); |
235 | if (err) |
236 | goto stop_and_cleanup; |
237 | |
238 | err = ext4_reserve_inode_write(handle, inode, iloc: &iloc); |
239 | if (err) |
240 | goto stop_and_cleanup; |
241 | |
242 | ext4_set_inode_flag(inode, bit: EXT4_INODE_VERITY); |
243 | ext4_set_inode_flags(inode, init: false); |
244 | err = ext4_mark_iloc_dirty(handle, inode, iloc: &iloc); |
245 | if (err) |
246 | goto stop_and_cleanup; |
247 | |
248 | ext4_journal_stop(handle); |
249 | |
250 | ext4_clear_inode_state(inode, bit: EXT4_STATE_VERITY_IN_PROGRESS); |
251 | return 0; |
252 | |
253 | stop_and_cleanup: |
254 | ext4_journal_stop(handle); |
255 | cleanup: |
256 | /* |
257 | * Verity failed to be enabled, so clean up by truncating any verity |
258 | * metadata that was written beyond i_size (both from cache and from |
259 | * disk), removing the inode from the orphan list (if it wasn't done |
260 | * already), and clearing EXT4_STATE_VERITY_IN_PROGRESS. |
261 | */ |
262 | truncate_inode_pages(inode->i_mapping, inode->i_size); |
263 | ext4_truncate(inode); |
264 | ext4_orphan_del(NULL, inode); |
265 | ext4_clear_inode_state(inode, bit: EXT4_STATE_VERITY_IN_PROGRESS); |
266 | return err; |
267 | } |
268 | |
269 | static int ext4_get_verity_descriptor_location(struct inode *inode, |
270 | size_t *desc_size_ret, |
271 | u64 *desc_pos_ret) |
272 | { |
273 | struct ext4_ext_path *path; |
274 | struct ext4_extent *last_extent; |
275 | u32 end_lblk; |
276 | u64 desc_size_pos; |
277 | __le32 desc_size_disk; |
278 | u32 desc_size; |
279 | u64 desc_pos; |
280 | int err; |
281 | |
282 | /* |
283 | * Descriptor size is in last 4 bytes of last allocated block. |
284 | * See ext4_write_verity_descriptor(). |
285 | */ |
286 | |
287 | if (!ext4_test_inode_flag(inode, bit: EXT4_INODE_EXTENTS)) { |
288 | EXT4_ERROR_INODE(inode, "verity file doesn't use extents" ); |
289 | return -EFSCORRUPTED; |
290 | } |
291 | |
292 | path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, flags: 0); |
293 | if (IS_ERR(ptr: path)) |
294 | return PTR_ERR(ptr: path); |
295 | |
296 | last_extent = path[path->p_depth].p_ext; |
297 | if (!last_extent) { |
298 | EXT4_ERROR_INODE(inode, "verity file has no extents" ); |
299 | ext4_free_ext_path(path); |
300 | return -EFSCORRUPTED; |
301 | } |
302 | |
303 | end_lblk = le32_to_cpu(last_extent->ee_block) + |
304 | ext4_ext_get_actual_len(ext: last_extent); |
305 | desc_size_pos = (u64)end_lblk << inode->i_blkbits; |
306 | ext4_free_ext_path(path); |
307 | |
308 | if (desc_size_pos < sizeof(desc_size_disk)) |
309 | goto bad; |
310 | desc_size_pos -= sizeof(desc_size_disk); |
311 | |
312 | err = pagecache_read(inode, buf: &desc_size_disk, count: sizeof(desc_size_disk), |
313 | pos: desc_size_pos); |
314 | if (err) |
315 | return err; |
316 | desc_size = le32_to_cpu(desc_size_disk); |
317 | |
318 | /* |
319 | * The descriptor is stored just before the desc_size_disk, but starting |
320 | * on a filesystem block boundary. |
321 | */ |
322 | |
323 | if (desc_size > INT_MAX || desc_size > desc_size_pos) |
324 | goto bad; |
325 | |
326 | desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode)); |
327 | if (desc_pos < ext4_verity_metadata_pos(inode)) |
328 | goto bad; |
329 | |
330 | *desc_size_ret = desc_size; |
331 | *desc_pos_ret = desc_pos; |
332 | return 0; |
333 | |
334 | bad: |
335 | EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor" ); |
336 | return -EFSCORRUPTED; |
337 | } |
338 | |
339 | static int ext4_get_verity_descriptor(struct inode *inode, void *buf, |
340 | size_t buf_size) |
341 | { |
342 | size_t desc_size = 0; |
343 | u64 desc_pos = 0; |
344 | int err; |
345 | |
346 | err = ext4_get_verity_descriptor_location(inode, desc_size_ret: &desc_size, desc_pos_ret: &desc_pos); |
347 | if (err) |
348 | return err; |
349 | |
350 | if (buf_size) { |
351 | if (desc_size > buf_size) |
352 | return -ERANGE; |
353 | err = pagecache_read(inode, buf, count: desc_size, pos: desc_pos); |
354 | if (err) |
355 | return err; |
356 | } |
357 | return desc_size; |
358 | } |
359 | |
360 | static struct page *ext4_read_merkle_tree_page(struct inode *inode, |
361 | pgoff_t index, |
362 | unsigned long num_ra_pages) |
363 | { |
364 | struct folio *folio; |
365 | |
366 | index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT; |
367 | |
368 | folio = __filemap_get_folio(mapping: inode->i_mapping, index, FGP_ACCESSED, gfp: 0); |
369 | if (IS_ERR(ptr: folio) || !folio_test_uptodate(folio)) { |
370 | DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index); |
371 | |
372 | if (!IS_ERR(ptr: folio)) |
373 | folio_put(folio); |
374 | else if (num_ra_pages > 1) |
375 | page_cache_ra_unbounded(&ractl, nr_to_read: num_ra_pages, lookahead_count: 0); |
376 | folio = read_mapping_folio(mapping: inode->i_mapping, index, NULL); |
377 | if (IS_ERR(ptr: folio)) |
378 | return ERR_CAST(ptr: folio); |
379 | } |
380 | return folio_file_page(folio, index); |
381 | } |
382 | |
383 | static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf, |
384 | u64 pos, unsigned int size) |
385 | { |
386 | pos += ext4_verity_metadata_pos(inode); |
387 | |
388 | return pagecache_write(inode, buf, count: size, pos); |
389 | } |
390 | |
391 | const struct fsverity_operations ext4_verityops = { |
392 | .begin_enable_verity = ext4_begin_enable_verity, |
393 | .end_enable_verity = ext4_end_enable_verity, |
394 | .get_verity_descriptor = ext4_get_verity_descriptor, |
395 | .read_merkle_tree_page = ext4_read_merkle_tree_page, |
396 | .write_merkle_tree_block = ext4_write_merkle_tree_block, |
397 | }; |
398 | |