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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * fs/f2fs/verity.c: fs-verity support for f2fs
4 *
5 * Copyright 2019 Google LLC
6 */
7
8/*
9 * Implementation of fsverity_operations for f2fs.
10 *
11 * Like ext4, f2fs stores the verity metadata (Merkle tree and
12 * fsverity_descriptor) past the end of the file, starting at the first 64K
13 * boundary beyond i_size. This approach works because (a) verity files are
14 * readonly, and (b) pages fully beyond i_size aren't visible to userspace but
15 * can be read/written internally by f2fs with only some relatively small
16 * changes to f2fs. Extended attributes cannot be used because (a) f2fs limits
17 * the total size of an inode's xattr entries to 4096 bytes, which wouldn't be
18 * enough for even a single Merkle tree block, and (b) f2fs encryption doesn't
19 * encrypt xattrs, yet the verity metadata *must* be encrypted when the file is
20 * because it contains hashes of the plaintext data.
21 *
22 * Using a 64K boundary rather than a 4K one keeps things ready for
23 * architectures with 64K pages, and it doesn't necessarily waste space on-disk
24 * since there can be a hole between i_size and the start of the Merkle tree.
25 */
26
27#include <linux/f2fs_fs.h>
28
29#include "f2fs.h"
30#include "xattr.h"
31
32#define F2FS_VERIFY_VER (1)
33
34static inline loff_t f2fs_verity_metadata_pos(const struct inode *inode)
35{
36 return round_up(inode->i_size, 65536);
37}
38
39/*
40 * Read some verity metadata from the inode. __vfs_read() can't be used because
41 * we need to read beyond i_size.
42 */
43static int pagecache_read(struct inode *inode, void *buf, size_t count,
44 loff_t pos)
45{
46 while (count) {
47 size_t n = min_t(size_t, count,
48 PAGE_SIZE - offset_in_page(pos));
49 struct page *page;
50 void *addr;
51
52 page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
53 NULL);
54 if (IS_ERR(page))
55 return PTR_ERR(page);
56
57 addr = kmap_atomic(page);
58 memcpy(buf, addr + offset_in_page(pos), n);
59 kunmap_atomic(addr);
60
61 put_page(page);
62
63 buf += n;
64 pos += n;
65 count -= n;
66 }
67 return 0;
68}
69
70/*
71 * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
72 * kernel_write() can't be used because the file descriptor is readonly.
73 */
74static int pagecache_write(struct inode *inode, const void *buf, size_t count,
75 loff_t pos)
76{
77 if (pos + count > inode->i_sb->s_maxbytes)
78 return -EFBIG;
79
80 while (count) {
81 size_t n = min_t(size_t, count,
82 PAGE_SIZE - offset_in_page(pos));
83 struct page *page;
84 void *fsdata;
85 void *addr;
86 int res;
87
88 res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0,
89 &page, &fsdata);
90 if (res)
91 return res;
92
93 addr = kmap_atomic(page);
94 memcpy(addr + offset_in_page(pos), buf, n);
95 kunmap_atomic(addr);
96
97 res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n,
98 page, fsdata);
99 if (res < 0)
100 return res;
101 if (res != n)
102 return -EIO;
103
104 buf += n;
105 pos += n;
106 count -= n;
107 }
108 return 0;
109}
110
111/*
112 * Format of f2fs verity xattr. This points to the location of the verity
113 * descriptor within the file data rather than containing it directly because
114 * the verity descriptor *must* be encrypted when f2fs encryption is used. But,
115 * f2fs encryption does not encrypt xattrs.
116 */
117struct fsverity_descriptor_location {
118 __le32 version;
119 __le32 size;
120 __le64 pos;
121};
122
123static int f2fs_begin_enable_verity(struct file *filp)
124{
125 struct inode *inode = file_inode(filp);
126 int err;
127
128 if (f2fs_verity_in_progress(inode))
129 return -EBUSY;
130
131 if (f2fs_is_atomic_file(inode) || f2fs_is_volatile_file(inode))
132 return -EOPNOTSUPP;
133
134 /*
135 * Since the file was opened readonly, we have to initialize the quotas
136 * here and not rely on ->open() doing it. This must be done before
137 * evicting the inline data.
138 */
139 err = dquot_initialize(inode);
140 if (err)
141 return err;
142
143 err = f2fs_convert_inline_inode(inode);
144 if (err)
145 return err;
146
147 set_inode_flag(inode, FI_VERITY_IN_PROGRESS);
148 return 0;
149}
150
151static int f2fs_end_enable_verity(struct file *filp, const void *desc,
152 size_t desc_size, u64 merkle_tree_size)
153{
154 struct inode *inode = file_inode(filp);
155 struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
156 u64 desc_pos = f2fs_verity_metadata_pos(inode) + merkle_tree_size;
157 struct fsverity_descriptor_location dloc = {
158 .version = cpu_to_le32(F2FS_VERIFY_VER),
159 .size = cpu_to_le32(desc_size),
160 .pos = cpu_to_le64(desc_pos),
161 };
162 int err = 0, err2 = 0;
163
164 /*
165 * If an error already occurred (which fs/verity/ signals by passing
166 * desc == NULL), then only clean-up is needed.
167 */
168 if (desc == NULL)
169 goto cleanup;
170
171 /* Append the verity descriptor. */
172 err = pagecache_write(inode, desc, desc_size, desc_pos);
173 if (err)
174 goto cleanup;
175
176 /*
177 * Write all pages (both data and verity metadata). Note that this must
178 * happen before clearing FI_VERITY_IN_PROGRESS; otherwise pages beyond
179 * i_size won't be written properly. For crash consistency, this also
180 * must happen before the verity inode flag gets persisted.
181 */
182 err = filemap_write_and_wait(inode->i_mapping);
183 if (err)
184 goto cleanup;
185
186 /* Set the verity xattr. */
187 err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
188 F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
189 NULL, XATTR_CREATE);
190 if (err)
191 goto cleanup;
192
193 /* Finally, set the verity inode flag. */
194 file_set_verity(inode);
195 f2fs_set_inode_flags(inode);
196 f2fs_mark_inode_dirty_sync(inode, true);
197
198 clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
199 return 0;
200
201cleanup:
202 /*
203 * Verity failed to be enabled, so clean up by truncating any verity
204 * metadata that was written beyond i_size (both from cache and from
205 * disk) and clearing FI_VERITY_IN_PROGRESS.
206 *
207 * Taking i_gc_rwsem[WRITE] is needed to stop f2fs garbage collection
208 * from re-instantiating cached pages we are truncating (since unlike
209 * normal file accesses, garbage collection isn't limited by i_size).
210 */
211 down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
212 truncate_inode_pages(inode->i_mapping, inode->i_size);
213 err2 = f2fs_truncate(inode);
214 if (err2) {
215 f2fs_err(sbi, "Truncating verity metadata failed (errno=%d)",
216 err2);
217 set_sbi_flag(sbi, SBI_NEED_FSCK);
218 }
219 up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
220 clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
221 return err ?: err2;
222}
223
224static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
225 size_t buf_size)
226{
227 struct fsverity_descriptor_location dloc;
228 int res;
229 u32 size;
230 u64 pos;
231
232 /* Get the descriptor location */
233 res = f2fs_getxattr(inode, F2FS_XATTR_INDEX_VERITY,
234 F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc), NULL);
235 if (res < 0 && res != -ERANGE)
236 return res;
237 if (res != sizeof(dloc) || dloc.version != cpu_to_le32(F2FS_VERIFY_VER)) {
238 f2fs_warn(F2FS_I_SB(inode), "unknown verity xattr format");
239 return -EINVAL;
240 }
241 size = le32_to_cpu(dloc.size);
242 pos = le64_to_cpu(dloc.pos);
243
244 /* Get the descriptor */
245 if (pos + size < pos || pos + size > inode->i_sb->s_maxbytes ||
246 pos < f2fs_verity_metadata_pos(inode) || size > INT_MAX) {
247 f2fs_warn(F2FS_I_SB(inode), "invalid verity xattr");
248 return -EFSCORRUPTED;
249 }
250 if (buf_size) {
251 if (size > buf_size)
252 return -ERANGE;
253 res = pagecache_read(inode, buf, size, pos);
254 if (res)
255 return res;
256 }
257 return size;
258}
259
260static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
261 pgoff_t index,
262 unsigned long num_ra_pages)
263{
264 DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
265 struct page *page;
266
267 index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
268
269 page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
270 if (!page || !PageUptodate(page)) {
271 if (page)
272 put_page(page);
273 else if (num_ra_pages > 1)
274 page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
275 page = read_mapping_page(inode->i_mapping, index, NULL);
276 }
277 return page;
278}
279
280static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
281 u64 index, int log_blocksize)
282{
283 loff_t pos = f2fs_verity_metadata_pos(inode) + (index << log_blocksize);
284
285 return pagecache_write(inode, buf, 1 << log_blocksize, pos);
286}
287
288const struct fsverity_operations f2fs_verityops = {
289 .begin_enable_verity = f2fs_begin_enable_verity,
290 .end_enable_verity = f2fs_end_enable_verity,
291 .get_verity_descriptor = f2fs_get_verity_descriptor,
292 .read_merkle_tree_page = f2fs_read_merkle_tree_page,
293 .write_merkle_tree_block = f2fs_write_merkle_tree_block,
294};