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1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | /* | |
3 | * fs-verity: read-only file-based authenticity protection | |
4 | * | |
5 | * This header declares the interface between the fs/verity/ support layer and | |
6 | * filesystems that support fs-verity. | |
7 | * | |
8 | * Copyright 2019 Google LLC | |
9 | */ | |
10 | ||
11 | #ifndef _LINUX_FSVERITY_H | |
12 | #define _LINUX_FSVERITY_H | |
13 | ||
14 | #include <linux/fs.h> | |
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15 | #include <crypto/hash_info.h> |
16 | #include <crypto/sha2.h> | |
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17 | #include <uapi/linux/fsverity.h> |
18 | ||
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19 | /* |
20 | * Largest digest size among all hash algorithms supported by fs-verity. | |
21 | * Currently assumed to be <= size of fsverity_descriptor::root_hash. | |
22 | */ | |
23 | #define FS_VERITY_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE | |
24 | ||
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25 | /* Arbitrary limit to bound the kmalloc() size. Can be changed. */ |
26 | #define FS_VERITY_MAX_DESCRIPTOR_SIZE 16384 | |
27 | ||
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28 | /* Verity operations for filesystems */ |
29 | struct fsverity_operations { | |
30 | ||
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31 | /** |
32 | * Begin enabling verity on the given file. | |
33 | * | |
34 | * @filp: a readonly file descriptor for the file | |
35 | * | |
36 | * The filesystem must do any needed filesystem-specific preparations | |
37 | * for enabling verity, e.g. evicting inline data. It also must return | |
38 | * -EBUSY if verity is already being enabled on the given file. | |
39 | * | |
40 | * i_rwsem is held for write. | |
41 | * | |
42 | * Return: 0 on success, -errno on failure | |
43 | */ | |
44 | int (*begin_enable_verity)(struct file *filp); | |
45 | ||
46 | /** | |
47 | * End enabling verity on the given file. | |
48 | * | |
49 | * @filp: a readonly file descriptor for the file | |
50 | * @desc: the verity descriptor to write, or NULL on failure | |
51 | * @desc_size: size of verity descriptor, or 0 on failure | |
52 | * @merkle_tree_size: total bytes the Merkle tree took up | |
53 | * | |
54 | * If desc == NULL, then enabling verity failed and the filesystem only | |
55 | * must do any necessary cleanups. Else, it must also store the given | |
56 | * verity descriptor to a fs-specific location associated with the inode | |
57 | * and do any fs-specific actions needed to mark the inode as a verity | |
58 | * inode, e.g. setting a bit in the on-disk inode. The filesystem is | |
59 | * also responsible for setting the S_VERITY flag in the VFS inode. | |
60 | * | |
61 | * i_rwsem is held for write, but it may have been dropped between | |
62 | * ->begin_enable_verity() and ->end_enable_verity(). | |
63 | * | |
64 | * Return: 0 on success, -errno on failure | |
65 | */ | |
66 | int (*end_enable_verity)(struct file *filp, const void *desc, | |
67 | size_t desc_size, u64 merkle_tree_size); | |
68 | ||
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69 | /** |
70 | * Get the verity descriptor of the given inode. | |
71 | * | |
72 | * @inode: an inode with the S_VERITY flag set | |
73 | * @buf: buffer in which to place the verity descriptor | |
74 | * @bufsize: size of @buf, or 0 to retrieve the size only | |
75 | * | |
76 | * If bufsize == 0, then the size of the verity descriptor is returned. | |
77 | * Otherwise the verity descriptor is written to 'buf' and its actual | |
78 | * size is returned; -ERANGE is returned if it's too large. This may be | |
79 | * called by multiple processes concurrently on the same inode. | |
80 | * | |
81 | * Return: the size on success, -errno on failure | |
82 | */ | |
83 | int (*get_verity_descriptor)(struct inode *inode, void *buf, | |
84 | size_t bufsize); | |
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85 | |
86 | /** | |
87 | * Read a Merkle tree page of the given inode. | |
88 | * | |
89 | * @inode: the inode | |
90 | * @index: 0-based index of the page within the Merkle tree | |
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91 | * @num_ra_pages: The number of Merkle tree pages that should be |
92 | * prefetched starting at @index if the page at @index | |
93 | * isn't already cached. Implementations may ignore this | |
94 | * argument; it's only a performance optimization. | |
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95 | * |
96 | * This can be called at any time on an open verity file, as well as | |
97 | * between ->begin_enable_verity() and ->end_enable_verity(). It may be | |
98 | * called by multiple processes concurrently, even with the same page. | |
99 | * | |
100 | * Note that this must retrieve a *page*, not necessarily a *block*. | |
101 | * | |
102 | * Return: the page on success, ERR_PTR() on failure | |
103 | */ | |
104 | struct page *(*read_merkle_tree_page)(struct inode *inode, | |
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105 | pgoff_t index, |
106 | unsigned long num_ra_pages); | |
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107 | |
108 | /** | |
109 | * Write a Merkle tree block to the given inode. | |
110 | * | |
111 | * @inode: the inode for which the Merkle tree is being built | |
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112 | * @buf: the Merkle tree block to write |
113 | * @pos: the position of the block in the Merkle tree (in bytes) | |
114 | * @size: the Merkle tree block size (in bytes) | |
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115 | * |
116 | * This is only called between ->begin_enable_verity() and | |
117 | * ->end_enable_verity(). | |
118 | * | |
119 | * Return: 0 on success, -errno on failure | |
120 | */ | |
121 | int (*write_merkle_tree_block)(struct inode *inode, const void *buf, | |
72ea15f0 | 122 | u64 pos, unsigned int size); |
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123 | }; |
124 | ||
125 | #ifdef CONFIG_FS_VERITY | |
126 | ||
127 | static inline struct fsverity_info *fsverity_get_info(const struct inode *inode) | |
128 | { | |
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129 | /* |
130 | * Pairs with the cmpxchg_release() in fsverity_set_info(). | |
131 | * I.e., another task may publish ->i_verity_info concurrently, | |
132 | * executing a RELEASE barrier. We need to use smp_load_acquire() here | |
133 | * to safely ACQUIRE the memory the other task published. | |
134 | */ | |
135 | return smp_load_acquire(&inode->i_verity_info); | |
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136 | } |
137 | ||
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138 | /* enable.c */ |
139 | ||
9cd6b593 | 140 | int fsverity_ioctl_enable(struct file *filp, const void __user *arg); |
3fda4c61 | 141 | |
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142 | /* measure.c */ |
143 | ||
9cd6b593 | 144 | int fsverity_ioctl_measure(struct file *filp, void __user *arg); |
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145 | int fsverity_get_digest(struct inode *inode, |
146 | u8 digest[FS_VERITY_MAX_DIGEST_SIZE], | |
147 | enum hash_algo *alg); | |
4dd893d8 | 148 | |
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149 | /* open.c */ |
150 | ||
a6528a96 | 151 | int __fsverity_file_open(struct inode *inode, struct file *filp); |
01d90c07 | 152 | int __fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr); |
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153 | void __fsverity_cleanup_inode(struct inode *inode); |
154 | ||
155 | /** | |
156 | * fsverity_cleanup_inode() - free the inode's verity info, if present | |
157 | * @inode: an inode being evicted | |
158 | * | |
159 | * Filesystems must call this on inode eviction to free ->i_verity_info. | |
160 | */ | |
161 | static inline void fsverity_cleanup_inode(struct inode *inode) | |
162 | { | |
163 | if (inode->i_verity_info) | |
164 | __fsverity_cleanup_inode(inode); | |
165 | } | |
fd2d1acf | 166 | |
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167 | /* read_metadata.c */ |
168 | ||
169 | int fsverity_ioctl_read_metadata(struct file *filp, const void __user *uarg); | |
170 | ||
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171 | /* verify.c */ |
172 | ||
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173 | bool fsverity_verify_page(struct page *page); |
174 | void fsverity_verify_bio(struct bio *bio); | |
175 | void fsverity_enqueue_verify_work(struct work_struct *work); | |
8a1d0f9c | 176 | |
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177 | #else /* !CONFIG_FS_VERITY */ |
178 | ||
179 | static inline struct fsverity_info *fsverity_get_info(const struct inode *inode) | |
180 | { | |
181 | return NULL; | |
182 | } | |
183 | ||
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184 | /* enable.c */ |
185 | ||
186 | static inline int fsverity_ioctl_enable(struct file *filp, | |
187 | const void __user *arg) | |
188 | { | |
189 | return -EOPNOTSUPP; | |
190 | } | |
191 | ||
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192 | /* measure.c */ |
193 | ||
194 | static inline int fsverity_ioctl_measure(struct file *filp, void __user *arg) | |
195 | { | |
196 | return -EOPNOTSUPP; | |
197 | } | |
198 | ||
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199 | static inline int fsverity_get_digest(struct inode *inode, |
200 | u8 digest[FS_VERITY_MAX_DIGEST_SIZE], | |
201 | enum hash_algo *alg) | |
202 | { | |
203 | return -EOPNOTSUPP; | |
204 | } | |
205 | ||
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206 | /* open.c */ |
207 | ||
a6528a96 | 208 | static inline int __fsverity_file_open(struct inode *inode, struct file *filp) |
fd2d1acf | 209 | { |
a6528a96 | 210 | return -EOPNOTSUPP; |
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211 | } |
212 | ||
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213 | static inline int __fsverity_prepare_setattr(struct dentry *dentry, |
214 | struct iattr *attr) | |
c1d9b584 | 215 | { |
01d90c07 | 216 | return -EOPNOTSUPP; |
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217 | } |
218 | ||
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219 | static inline void fsverity_cleanup_inode(struct inode *inode) |
220 | { | |
221 | } | |
222 | ||
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223 | /* read_metadata.c */ |
224 | ||
225 | static inline int fsverity_ioctl_read_metadata(struct file *filp, | |
226 | const void __user *uarg) | |
227 | { | |
228 | return -EOPNOTSUPP; | |
229 | } | |
230 | ||
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231 | /* verify.c */ |
232 | ||
233 | static inline bool fsverity_verify_page(struct page *page) | |
234 | { | |
235 | WARN_ON(1); | |
236 | return false; | |
237 | } | |
238 | ||
239 | static inline void fsverity_verify_bio(struct bio *bio) | |
240 | { | |
241 | WARN_ON(1); | |
242 | } | |
243 | ||
244 | static inline void fsverity_enqueue_verify_work(struct work_struct *work) | |
245 | { | |
246 | WARN_ON(1); | |
247 | } | |
248 | ||
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249 | #endif /* !CONFIG_FS_VERITY */ |
250 | ||
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251 | /** |
252 | * fsverity_active() - do reads from the inode need to go through fs-verity? | |
6377a38b | 253 | * @inode: inode to check |
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254 | * |
255 | * This checks whether ->i_verity_info has been set. | |
256 | * | |
704528d8 | 257 | * Filesystems call this from ->readahead() to check whether the pages need to |
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258 | * be verified or not. Don't use IS_VERITY() for this purpose; it's subject to |
259 | * a race condition where the file is being read concurrently with | |
260 | * FS_IOC_ENABLE_VERITY completing. (S_VERITY is set before ->i_verity_info.) | |
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261 | * |
262 | * Return: true if reads need to go through fs-verity, otherwise false | |
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263 | */ |
264 | static inline bool fsverity_active(const struct inode *inode) | |
265 | { | |
266 | return fsverity_get_info(inode) != NULL; | |
267 | } | |
268 | ||
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269 | /** |
270 | * fsverity_file_open() - prepare to open a verity file | |
271 | * @inode: the inode being opened | |
272 | * @filp: the struct file being set up | |
273 | * | |
274 | * When opening a verity file, deny the open if it is for writing. Otherwise, | |
275 | * set up the inode's ->i_verity_info if not already done. | |
276 | * | |
277 | * When combined with fscrypt, this must be called after fscrypt_file_open(). | |
278 | * Otherwise, we won't have the key set up to decrypt the verity metadata. | |
279 | * | |
280 | * Return: 0 on success, -errno on failure | |
281 | */ | |
282 | static inline int fsverity_file_open(struct inode *inode, struct file *filp) | |
283 | { | |
284 | if (IS_VERITY(inode)) | |
285 | return __fsverity_file_open(inode, filp); | |
286 | return 0; | |
287 | } | |
288 | ||
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289 | /** |
290 | * fsverity_prepare_setattr() - prepare to change a verity inode's attributes | |
291 | * @dentry: dentry through which the inode is being changed | |
292 | * @attr: attributes to change | |
293 | * | |
294 | * Verity files are immutable, so deny truncates. This isn't covered by the | |
295 | * open-time check because sys_truncate() takes a path, not a file descriptor. | |
296 | * | |
297 | * Return: 0 on success, -errno on failure | |
298 | */ | |
299 | static inline int fsverity_prepare_setattr(struct dentry *dentry, | |
300 | struct iattr *attr) | |
301 | { | |
302 | if (IS_VERITY(d_inode(dentry))) | |
303 | return __fsverity_prepare_setattr(dentry, attr); | |
304 | return 0; | |
305 | } | |
306 | ||
fd2d1acf | 307 | #endif /* _LINUX_FSVERITY_H */ |