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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
32static 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 */
41static 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 */
72static 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;
83 void *addr;
84 int res;
85
86 res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0,
87 &page, &fsdata);
88 if (res)
89 return res;
90
91 addr = kmap_atomic(page);
92 memcpy(addr + offset_in_page(pos), buf, n);
93 kunmap_atomic(addr);
94
95 res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n,
96 page, fsdata);
97 if (res < 0)
98 return res;
99 if (res != n)
100 return -EIO;
101
102 buf += n;
103 pos += n;
104 count -= n;
105 }
106 return 0;
107}
108
109static int ext4_begin_enable_verity(struct file *filp)
110{
111 struct inode *inode = file_inode(filp);
112 const int credits = 2; /* superblock and inode for ext4_orphan_add() */
113 handle_t *handle;
114 int err;
115
116 if (IS_DAX(inode) || ext4_test_inode_flag(inode, EXT4_INODE_DAX))
117 return -EINVAL;
118
119 if (ext4_verity_in_progress(inode))
120 return -EBUSY;
121
122 /*
123 * Since the file was opened readonly, we have to initialize the jbd
124 * inode and quotas here and not rely on ->open() doing it. This must
125 * be done before evicting the inline data.
126 */
127
128 err = ext4_inode_attach_jinode(inode);
129 if (err)
130 return err;
131
132 err = dquot_initialize(inode);
133 if (err)
134 return err;
135
136 err = ext4_convert_inline_data(inode);
137 if (err)
138 return err;
139
140 if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
141 ext4_warning_inode(inode,
142 "verity is only allowed on extent-based files");
143 return -EOPNOTSUPP;
144 }
145
146 /*
147 * ext4 uses the last allocated block to find the verity descriptor, so
148 * we must remove any other blocks past EOF which might confuse things.
149 */
150 err = ext4_truncate(inode);
151 if (err)
152 return err;
153
154 handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
155 if (IS_ERR(handle))
156 return PTR_ERR(handle);
157
158 err = ext4_orphan_add(handle, inode);
159 if (err == 0)
160 ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
161
162 ext4_journal_stop(handle);
163 return err;
164}
165
166/*
167 * ext4 stores the verity descriptor beginning on the next filesystem block
168 * boundary after the Merkle tree. Then, the descriptor size is stored in the
169 * last 4 bytes of the last allocated filesystem block --- which is either the
170 * block in which the descriptor ends, or the next block after that if there
171 * weren't at least 4 bytes remaining.
172 *
173 * We can't simply store the descriptor in an xattr because it *must* be
174 * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt
175 * xattrs. Also, if the descriptor includes a large signature blob it may be
176 * too large to store in an xattr without the EA_INODE feature.
177 */
178static int ext4_write_verity_descriptor(struct inode *inode, const void *desc,
179 size_t desc_size, u64 merkle_tree_size)
180{
181 const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +
182 merkle_tree_size, i_blocksize(inode));
183 const u64 desc_end = desc_pos + desc_size;
184 const __le32 desc_size_disk = cpu_to_le32(desc_size);
185 const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),
186 i_blocksize(inode)) -
187 sizeof(desc_size_disk);
188 int err;
189
190 err = pagecache_write(inode, desc, desc_size, desc_pos);
191 if (err)
192 return err;
193
194 return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),
195 desc_size_pos);
196}
197
198static int ext4_end_enable_verity(struct file *filp, const void *desc,
199 size_t desc_size, u64 merkle_tree_size)
200{
201 struct inode *inode = file_inode(filp);
202 const int credits = 2; /* superblock and inode for ext4_orphan_del() */
203 handle_t *handle;
204 int err = 0;
205 int err2;
206
207 if (desc != NULL) {
208 /* Succeeded; write the verity descriptor. */
209 err = ext4_write_verity_descriptor(inode, desc, desc_size,
210 merkle_tree_size);
211
212 /* Write all pages before clearing VERITY_IN_PROGRESS. */
213 if (!err)
214 err = filemap_write_and_wait(inode->i_mapping);
215 }
216
217 /* If we failed, truncate anything we wrote past i_size. */
218 if (desc == NULL || err)
219 ext4_truncate(inode);
220
221 /*
222 * We must always clean up by clearing EXT4_STATE_VERITY_IN_PROGRESS and
223 * deleting the inode from the orphan list, even if something failed.
224 * If everything succeeded, we'll also set the verity bit in the same
225 * transaction.
226 */
227
228 ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
229
230 handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
231 if (IS_ERR(handle)) {
232 ext4_orphan_del(NULL, inode);
233 return PTR_ERR(handle);
234 }
235
236 err2 = ext4_orphan_del(handle, inode);
237 if (err2)
238 goto out_stop;
239
240 if (desc != NULL && !err) {
241 struct ext4_iloc iloc;
242
243 err = ext4_reserve_inode_write(handle, inode, &iloc);
244 if (err)
245 goto out_stop;
246 ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
247 ext4_set_inode_flags(inode, false);
248 err = ext4_mark_iloc_dirty(handle, inode, &iloc);
249 }
250out_stop:
251 ext4_journal_stop(handle);
252 return err ?: err2;
253}
254
255static int ext4_get_verity_descriptor_location(struct inode *inode,
256 size_t *desc_size_ret,
257 u64 *desc_pos_ret)
258{
259 struct ext4_ext_path *path;
260 struct ext4_extent *last_extent;
261 u32 end_lblk;
262 u64 desc_size_pos;
263 __le32 desc_size_disk;
264 u32 desc_size;
265 u64 desc_pos;
266 int err;
267
268 /*
269 * Descriptor size is in last 4 bytes of last allocated block.
270 * See ext4_write_verity_descriptor().
271 */
272
273 if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
274 EXT4_ERROR_INODE(inode, "verity file doesn't use extents");
275 return -EFSCORRUPTED;
276 }
277
278 path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
279 if (IS_ERR(path))
280 return PTR_ERR(path);
281
282 last_extent = path[path->p_depth].p_ext;
283 if (!last_extent) {
284 EXT4_ERROR_INODE(inode, "verity file has no extents");
285 ext4_ext_drop_refs(path);
286 kfree(path);
287 return -EFSCORRUPTED;
288 }
289
290 end_lblk = le32_to_cpu(last_extent->ee_block) +
291 ext4_ext_get_actual_len(last_extent);
292 desc_size_pos = (u64)end_lblk << inode->i_blkbits;
293 ext4_ext_drop_refs(path);
294 kfree(path);
295
296 if (desc_size_pos < sizeof(desc_size_disk))
297 goto bad;
298 desc_size_pos -= sizeof(desc_size_disk);
299
300 err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),
301 desc_size_pos);
302 if (err)
303 return err;
304 desc_size = le32_to_cpu(desc_size_disk);
305
306 /*
307 * The descriptor is stored just before the desc_size_disk, but starting
308 * on a filesystem block boundary.
309 */
310
311 if (desc_size > INT_MAX || desc_size > desc_size_pos)
312 goto bad;
313
314 desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));
315 if (desc_pos < ext4_verity_metadata_pos(inode))
316 goto bad;
317
318 *desc_size_ret = desc_size;
319 *desc_pos_ret = desc_pos;
320 return 0;
321
322bad:
323 EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");
324 return -EFSCORRUPTED;
325}
326
327static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
328 size_t buf_size)
329{
330 size_t desc_size = 0;
331 u64 desc_pos = 0;
332 int err;
333
334 err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);
335 if (err)
336 return err;
337
338 if (buf_size) {
339 if (desc_size > buf_size)
340 return -ERANGE;
341 err = pagecache_read(inode, buf, desc_size, desc_pos);
342 if (err)
343 return err;
344 }
345 return desc_size;
346}
347
348static struct page *ext4_read_merkle_tree_page(struct inode *inode,
349 pgoff_t index,
350 unsigned long num_ra_pages)
351{
352 struct page *page;
353
354 index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
355
356 page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
357 if (!page || !PageUptodate(page)) {
358 if (page)
359 put_page(page);
360 else if (num_ra_pages > 1)
361 page_cache_readahead_unbounded(inode->i_mapping, NULL,
362 index, num_ra_pages, 0);
363 page = read_mapping_page(inode->i_mapping, index, NULL);
364 }
365 return page;
366}
367
368static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf,
369 u64 index, int log_blocksize)
370{
371 loff_t pos = ext4_verity_metadata_pos(inode) + (index << log_blocksize);
372
373 return pagecache_write(inode, buf, 1 << log_blocksize, pos);
374}
375
376const struct fsverity_operations ext4_verityops = {
377 .begin_enable_verity = ext4_begin_enable_verity,
378 .end_enable_verity = ext4_end_enable_verity,
379 .get_verity_descriptor = ext4_get_verity_descriptor,
380 .read_merkle_tree_page = ext4_read_merkle_tree_page,
381 .write_merkle_tree_block = ext4_write_merkle_tree_block,
382};