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
ext4_verity_metadata_pos(const struct inode * inode)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 */
pagecache_read(struct inode * inode,void * buf,size_t count,loff_t pos)41 static int pagecache_read(struct inode *inode, void *buf, size_t count,
42 loff_t pos)
43 {
44 while (count) {
45 size_t n = min_t(size_t, count,
46 PAGE_SIZE - offset_in_page(pos));
47 struct page *page;
48 void *addr;
49
50 page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
51 NULL);
52 if (IS_ERR(page))
53 return PTR_ERR(page);
54
55 addr = kmap_atomic(page);
56 memcpy(buf, addr + offset_in_page(pos), n);
57 kunmap_atomic(addr);
58
59 put_page(page);
60
61 buf += n;
62 pos += n;
63 count -= n;
64 }
65 return 0;
66 }
67
68 /*
69 * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
70 * kernel_write() can't be used because the file descriptor is readonly.
71 */
pagecache_write(struct inode * inode,const void * buf,size_t count,loff_t pos)72 static int pagecache_write(struct inode *inode, const void *buf, size_t count,
73 loff_t pos)
74 {
75 if (pos + count > inode->i_sb->s_maxbytes)
76 return -EFBIG;
77
78 while (count) {
79 size_t n = min_t(size_t, count,
80 PAGE_SIZE - offset_in_page(pos));
81 struct page *page;
82 void *fsdata = NULL;
83 int res;
84
85 res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0,
86 &page, &fsdata);
87 if (res)
88 return res;
89
90 memcpy_to_page(page, offset_in_page(pos), buf, n);
91
92 res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n,
93 page, fsdata);
94 if (res < 0)
95 return res;
96 if (res != n)
97 return -EIO;
98
99 buf += n;
100 pos += n;
101 count -= n;
102 }
103 return 0;
104 }
105
ext4_begin_enable_verity(struct file * filp)106 static int ext4_begin_enable_verity(struct file *filp)
107 {
108 struct inode *inode = file_inode(filp);
109 const int credits = 2; /* superblock and inode for ext4_orphan_add() */
110 handle_t *handle;
111 int err;
112
113 if (ext4_verity_in_progress(inode))
114 return -EBUSY;
115
116 /*
117 * Since the file was opened readonly, we have to initialize the jbd
118 * inode and quotas here and not rely on ->open() doing it. This must
119 * be done before evicting the inline data.
120 */
121
122 err = ext4_inode_attach_jinode(inode);
123 if (err)
124 return err;
125
126 err = dquot_initialize(inode);
127 if (err)
128 return err;
129
130 err = ext4_convert_inline_data(inode);
131 if (err)
132 return err;
133
134 if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
135 ext4_warning_inode(inode,
136 "verity is only allowed on extent-based files");
137 return -EOPNOTSUPP;
138 }
139
140 /*
141 * ext4 uses the last allocated block to find the verity descriptor, so
142 * we must remove any other blocks past EOF which might confuse things.
143 */
144 err = ext4_truncate(inode);
145 if (err)
146 return err;
147
148 handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
149 if (IS_ERR(handle))
150 return PTR_ERR(handle);
151
152 err = ext4_orphan_add(handle, inode);
153 if (err == 0)
154 ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
155
156 ext4_journal_stop(handle);
157 return err;
158 }
159
160 /*
161 * ext4 stores the verity descriptor beginning on the next filesystem block
162 * boundary after the Merkle tree. Then, the descriptor size is stored in the
163 * last 4 bytes of the last allocated filesystem block --- which is either the
164 * block in which the descriptor ends, or the next block after that if there
165 * weren't at least 4 bytes remaining.
166 *
167 * We can't simply store the descriptor in an xattr because it *must* be
168 * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt
169 * xattrs. Also, if the descriptor includes a large signature blob it may be
170 * too large to store in an xattr without the EA_INODE feature.
171 */
ext4_write_verity_descriptor(struct inode * inode,const void * desc,size_t desc_size,u64 merkle_tree_size)172 static int ext4_write_verity_descriptor(struct inode *inode, const void *desc,
173 size_t desc_size, u64 merkle_tree_size)
174 {
175 const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +
176 merkle_tree_size, i_blocksize(inode));
177 const u64 desc_end = desc_pos + desc_size;
178 const __le32 desc_size_disk = cpu_to_le32(desc_size);
179 const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),
180 i_blocksize(inode)) -
181 sizeof(desc_size_disk);
182 int err;
183
184 err = pagecache_write(inode, desc, desc_size, desc_pos);
185 if (err)
186 return err;
187
188 return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),
189 desc_size_pos);
190 }
191
ext4_end_enable_verity(struct file * filp,const void * desc,size_t desc_size,u64 merkle_tree_size)192 static int ext4_end_enable_verity(struct file *filp, const void *desc,
193 size_t desc_size, u64 merkle_tree_size)
194 {
195 struct inode *inode = file_inode(filp);
196 const int credits = 2; /* superblock and inode for ext4_orphan_del() */
197 handle_t *handle;
198 struct ext4_iloc iloc;
199 int err = 0;
200
201 /*
202 * If an error already occurred (which fs/verity/ signals by passing
203 * desc == NULL), then only clean-up is needed.
204 */
205 if (desc == NULL)
206 goto cleanup;
207
208 /* Append the verity descriptor. */
209 err = ext4_write_verity_descriptor(inode, desc, desc_size,
210 merkle_tree_size);
211 if (err)
212 goto cleanup;
213
214 /*
215 * Write all pages (both data and verity metadata). Note that this must
216 * happen before clearing EXT4_STATE_VERITY_IN_PROGRESS; otherwise pages
217 * beyond i_size won't be written properly. For crash consistency, this
218 * also must happen before the verity inode flag gets persisted.
219 */
220 err = filemap_write_and_wait(inode->i_mapping);
221 if (err)
222 goto cleanup;
223
224 /*
225 * Finally, set the verity inode flag and remove the inode from the
226 * orphan list (in a single transaction).
227 */
228
229 handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
230 if (IS_ERR(handle)) {
231 err = PTR_ERR(handle);
232 goto cleanup;
233 }
234
235 err = ext4_orphan_del(handle, inode);
236 if (err)
237 goto stop_and_cleanup;
238
239 err = ext4_reserve_inode_write(handle, inode, &iloc);
240 if (err)
241 goto stop_and_cleanup;
242
243 ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
244 ext4_set_inode_flags(inode);
245 err = ext4_mark_iloc_dirty(handle, inode, &iloc);
246 if (err)
247 goto stop_and_cleanup;
248
249 ext4_journal_stop(handle);
250
251 ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
252 return 0;
253
254 stop_and_cleanup:
255 ext4_journal_stop(handle);
256 cleanup:
257 /*
258 * Verity failed to be enabled, so clean up by truncating any verity
259 * metadata that was written beyond i_size (both from cache and from
260 * disk), removing the inode from the orphan list (if it wasn't done
261 * already), and clearing EXT4_STATE_VERITY_IN_PROGRESS.
262 */
263 truncate_inode_pages(inode->i_mapping, inode->i_size);
264 ext4_truncate(inode);
265 ext4_orphan_del(NULL, inode);
266 ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
267 return err;
268 }
269
ext4_get_verity_descriptor_location(struct inode * inode,size_t * desc_size_ret,u64 * desc_pos_ret)270 static int ext4_get_verity_descriptor_location(struct inode *inode,
271 size_t *desc_size_ret,
272 u64 *desc_pos_ret)
273 {
274 struct ext4_ext_path *path;
275 struct ext4_extent *last_extent;
276 u32 end_lblk;
277 u64 desc_size_pos;
278 __le32 desc_size_disk;
279 u32 desc_size;
280 u64 desc_pos;
281 int err;
282
283 /*
284 * Descriptor size is in last 4 bytes of last allocated block.
285 * See ext4_write_verity_descriptor().
286 */
287
288 if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
289 EXT4_ERROR_INODE(inode, "verity file doesn't use extents");
290 return -EFSCORRUPTED;
291 }
292
293 path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
294 if (IS_ERR(path))
295 return PTR_ERR(path);
296
297 last_extent = path[path->p_depth].p_ext;
298 if (!last_extent) {
299 EXT4_ERROR_INODE(inode, "verity file has no extents");
300 ext4_ext_drop_refs(path);
301 kfree(path);
302 return -EFSCORRUPTED;
303 }
304
305 end_lblk = le32_to_cpu(last_extent->ee_block) +
306 ext4_ext_get_actual_len(last_extent);
307 desc_size_pos = (u64)end_lblk << inode->i_blkbits;
308 ext4_ext_drop_refs(path);
309 kfree(path);
310
311 if (desc_size_pos < sizeof(desc_size_disk))
312 goto bad;
313 desc_size_pos -= sizeof(desc_size_disk);
314
315 err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),
316 desc_size_pos);
317 if (err)
318 return err;
319 desc_size = le32_to_cpu(desc_size_disk);
320
321 /*
322 * The descriptor is stored just before the desc_size_disk, but starting
323 * on a filesystem block boundary.
324 */
325
326 if (desc_size > INT_MAX || desc_size > desc_size_pos)
327 goto bad;
328
329 desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));
330 if (desc_pos < ext4_verity_metadata_pos(inode))
331 goto bad;
332
333 *desc_size_ret = desc_size;
334 *desc_pos_ret = desc_pos;
335 return 0;
336
337 bad:
338 EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");
339 return -EFSCORRUPTED;
340 }
341
ext4_get_verity_descriptor(struct inode * inode,void * buf,size_t buf_size)342 static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
343 size_t buf_size)
344 {
345 size_t desc_size = 0;
346 u64 desc_pos = 0;
347 int err;
348
349 err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);
350 if (err)
351 return err;
352
353 if (buf_size) {
354 if (desc_size > buf_size)
355 return -ERANGE;
356 err = pagecache_read(inode, buf, desc_size, desc_pos);
357 if (err)
358 return err;
359 }
360 return desc_size;
361 }
362
363 /*
364 * Prefetch some pages from the file's Merkle tree.
365 *
366 * This is basically a stripped-down version of __do_page_cache_readahead()
367 * which works on pages past i_size.
368 */
ext4_merkle_tree_readahead(struct address_space * mapping,pgoff_t start_index,unsigned long count)369 static void ext4_merkle_tree_readahead(struct address_space *mapping,
370 pgoff_t start_index, unsigned long count)
371 {
372 LIST_HEAD(pages);
373 unsigned int nr_pages = 0;
374 struct page *page;
375 pgoff_t index;
376 struct blk_plug plug;
377
378 for (index = start_index; index < start_index + count; index++) {
379 page = xa_load(&mapping->i_pages, index);
380 if (!page || xa_is_value(page)) {
381 page = __page_cache_alloc(readahead_gfp_mask(mapping));
382 if (!page)
383 break;
384 page->index = index;
385 list_add(&page->lru, &pages);
386 nr_pages++;
387 }
388 }
389 blk_start_plug(&plug);
390 ext4_mpage_readpages(mapping, &pages, NULL, nr_pages, true);
391 blk_finish_plug(&plug);
392 }
393
ext4_read_merkle_tree_page(struct inode * inode,pgoff_t index,unsigned long num_ra_pages)394 static struct page *ext4_read_merkle_tree_page(struct inode *inode,
395 pgoff_t index,
396 unsigned long num_ra_pages)
397 {
398 struct page *page;
399
400 index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
401
402 page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
403 if (!page || !PageUptodate(page)) {
404 if (page)
405 put_page(page);
406 else if (num_ra_pages > 1)
407 ext4_merkle_tree_readahead(inode->i_mapping, index,
408 num_ra_pages);
409 page = read_mapping_page(inode->i_mapping, index, NULL);
410 }
411 return page;
412 }
413
ext4_write_merkle_tree_block(struct inode * inode,const void * buf,u64 index,int log_blocksize)414 static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf,
415 u64 index, int log_blocksize)
416 {
417 loff_t pos = ext4_verity_metadata_pos(inode) + (index << log_blocksize);
418
419 return pagecache_write(inode, buf, 1 << log_blocksize, pos);
420 }
421
422 const struct fsverity_operations ext4_verityops = {
423 .begin_enable_verity = ext4_begin_enable_verity,
424 .end_enable_verity = ext4_end_enable_verity,
425 .get_verity_descriptor = ext4_get_verity_descriptor,
426 .read_merkle_tree_page = ext4_read_merkle_tree_page,
427 .write_merkle_tree_block = ext4_write_merkle_tree_block,
428 };
429