Commit | Line | Data |
---|---|---|
4dd893d8 EB |
1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* | |
ed45e201 | 3 | * Ioctl to get a verity file's digest |
4dd893d8 EB |
4 | * |
5 | * Copyright 2019 Google LLC | |
6 | */ | |
7 | ||
8 | #include "fsverity_private.h" | |
9 | ||
67814c00 SL |
10 | #include <linux/bpf.h> |
11 | #include <linux/btf.h> | |
4dd893d8 EB |
12 | #include <linux/uaccess.h> |
13 | ||
14 | /** | |
ed45e201 EB |
15 | * fsverity_ioctl_measure() - get a verity file's digest |
16 | * @filp: file to get digest of | |
6377a38b | 17 | * @_uarg: user pointer to fsverity_digest |
4dd893d8 | 18 | * |
ed45e201 EB |
19 | * Retrieve the file digest that the kernel is enforcing for reads from a verity |
20 | * file. See the "FS_IOC_MEASURE_VERITY" section of | |
4dd893d8 EB |
21 | * Documentation/filesystems/fsverity.rst for the documentation. |
22 | * | |
23 | * Return: 0 on success, -errno on failure | |
24 | */ | |
25 | int fsverity_ioctl_measure(struct file *filp, void __user *_uarg) | |
26 | { | |
27 | const struct inode *inode = file_inode(filp); | |
28 | struct fsverity_digest __user *uarg = _uarg; | |
29 | const struct fsverity_info *vi; | |
30 | const struct fsverity_hash_alg *hash_alg; | |
31 | struct fsverity_digest arg; | |
32 | ||
33 | vi = fsverity_get_info(inode); | |
34 | if (!vi) | |
35 | return -ENODATA; /* not a verity file */ | |
36 | hash_alg = vi->tree_params.hash_alg; | |
37 | ||
38 | /* | |
39 | * The user specifies the digest_size their buffer has space for; we can | |
40 | * return the digest if it fits in the available space. We write back | |
41 | * the actual size, which may be shorter than the user-specified size. | |
42 | */ | |
43 | ||
44 | if (get_user(arg.digest_size, &uarg->digest_size)) | |
45 | return -EFAULT; | |
46 | if (arg.digest_size < hash_alg->digest_size) | |
47 | return -EOVERFLOW; | |
48 | ||
49 | memset(&arg, 0, sizeof(arg)); | |
50 | arg.digest_algorithm = hash_alg - fsverity_hash_algs; | |
51 | arg.digest_size = hash_alg->digest_size; | |
52 | ||
53 | if (copy_to_user(uarg, &arg, sizeof(arg))) | |
54 | return -EFAULT; | |
55 | ||
ed45e201 | 56 | if (copy_to_user(uarg->digest, vi->file_digest, hash_alg->digest_size)) |
4dd893d8 EB |
57 | return -EFAULT; |
58 | ||
59 | return 0; | |
60 | } | |
61 | EXPORT_SYMBOL_GPL(fsverity_ioctl_measure); | |
246d9216 MZ |
62 | |
63 | /** | |
64 | * fsverity_get_digest() - get a verity file's digest | |
65 | * @inode: inode to get digest of | |
74836ecb EB |
66 | * @raw_digest: (out) the raw file digest |
67 | * @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value | |
68 | * @halg: (out) the digest's algorithm, as a HASH_ALGO_* value | |
246d9216 | 69 | * |
74836ecb EB |
70 | * Retrieves the fsverity digest of the given file. The file must have been |
71 | * opened at least once since the inode was last loaded into the inode cache; | |
72 | * otherwise this function will not recognize when fsverity is enabled. | |
246d9216 | 73 | * |
74836ecb EB |
74 | * The file's fsverity digest consists of @raw_digest in combination with either |
75 | * @alg or @halg. (The caller can choose which one of @alg or @halg to use.) | |
76 | * | |
77 | * IMPORTANT: Callers *must* make use of one of the two algorithm IDs, since | |
78 | * @raw_digest is meaningless without knowing which algorithm it uses! fsverity | |
79 | * provides no security guarantee for users who ignore the algorithm ID, even if | |
80 | * they use the digest size (since algorithms can share the same digest size). | |
81 | * | |
82 | * Return: The size of the raw digest in bytes, or 0 if the file doesn't have | |
83 | * fsverity enabled. | |
246d9216 MZ |
84 | */ |
85 | int fsverity_get_digest(struct inode *inode, | |
74836ecb EB |
86 | u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE], |
87 | u8 *alg, enum hash_algo *halg) | |
246d9216 MZ |
88 | { |
89 | const struct fsverity_info *vi; | |
90 | const struct fsverity_hash_alg *hash_alg; | |
246d9216 MZ |
91 | |
92 | vi = fsverity_get_info(inode); | |
93 | if (!vi) | |
74836ecb | 94 | return 0; /* not a verity file */ |
246d9216 MZ |
95 | |
96 | hash_alg = vi->tree_params.hash_alg; | |
74836ecb EB |
97 | memcpy(raw_digest, vi->file_digest, hash_alg->digest_size); |
98 | if (alg) | |
99 | *alg = hash_alg - fsverity_hash_algs; | |
100 | if (halg) | |
101 | *halg = hash_alg->algo_id; | |
102 | return hash_alg->digest_size; | |
246d9216 | 103 | } |
74836ecb | 104 | EXPORT_SYMBOL_GPL(fsverity_get_digest); |
67814c00 SL |
105 | |
106 | #ifdef CONFIG_BPF_SYSCALL | |
107 | ||
108 | /* bpf kfuncs */ | |
109 | __bpf_kfunc_start_defs(); | |
110 | ||
111 | /** | |
112 | * bpf_get_fsverity_digest: read fsverity digest of file | |
113 | * @file: file to get digest from | |
114 | * @digest_ptr: (out) dynptr for struct fsverity_digest | |
115 | * | |
116 | * Read fsverity_digest of *file* into *digest_ptr*. | |
117 | * | |
118 | * Return: 0 on success, a negative value on error. | |
119 | */ | |
120 | __bpf_kfunc int bpf_get_fsverity_digest(struct file *file, struct bpf_dynptr_kern *digest_ptr) | |
121 | { | |
122 | const struct inode *inode = file_inode(file); | |
123 | u32 dynptr_sz = __bpf_dynptr_size(digest_ptr); | |
124 | struct fsverity_digest *arg; | |
125 | const struct fsverity_info *vi; | |
126 | const struct fsverity_hash_alg *hash_alg; | |
127 | int out_digest_sz; | |
128 | ||
129 | if (dynptr_sz < sizeof(struct fsverity_digest)) | |
130 | return -EINVAL; | |
131 | ||
132 | arg = __bpf_dynptr_data_rw(digest_ptr, dynptr_sz); | |
133 | if (!arg) | |
134 | return -EINVAL; | |
135 | ||
136 | if (!IS_ALIGNED((uintptr_t)arg, __alignof__(*arg))) | |
137 | return -EINVAL; | |
138 | ||
139 | vi = fsverity_get_info(inode); | |
140 | if (!vi) | |
141 | return -ENODATA; /* not a verity file */ | |
142 | ||
143 | hash_alg = vi->tree_params.hash_alg; | |
144 | ||
145 | arg->digest_algorithm = hash_alg - fsverity_hash_algs; | |
146 | arg->digest_size = hash_alg->digest_size; | |
147 | ||
148 | out_digest_sz = dynptr_sz - sizeof(struct fsverity_digest); | |
149 | ||
150 | /* copy digest */ | |
151 | memcpy(arg->digest, vi->file_digest, min_t(int, hash_alg->digest_size, out_digest_sz)); | |
152 | ||
153 | /* fill the extra buffer with zeros */ | |
154 | if (out_digest_sz > hash_alg->digest_size) | |
155 | memset(arg->digest + arg->digest_size, 0, out_digest_sz - hash_alg->digest_size); | |
156 | ||
157 | return 0; | |
158 | } | |
159 | ||
160 | __bpf_kfunc_end_defs(); | |
161 | ||
162 | BTF_SET8_START(fsverity_set_ids) | |
163 | BTF_ID_FLAGS(func, bpf_get_fsverity_digest, KF_TRUSTED_ARGS) | |
164 | BTF_SET8_END(fsverity_set_ids) | |
165 | ||
166 | static int bpf_get_fsverity_digest_filter(const struct bpf_prog *prog, u32 kfunc_id) | |
167 | { | |
168 | if (!btf_id_set8_contains(&fsverity_set_ids, kfunc_id)) | |
169 | return 0; | |
170 | ||
171 | /* Only allow to attach from LSM hooks, to avoid recursion */ | |
172 | return prog->type != BPF_PROG_TYPE_LSM ? -EACCES : 0; | |
173 | } | |
174 | ||
175 | static const struct btf_kfunc_id_set bpf_fsverity_set = { | |
176 | .owner = THIS_MODULE, | |
177 | .set = &fsverity_set_ids, | |
178 | .filter = bpf_get_fsverity_digest_filter, | |
179 | }; | |
180 | ||
181 | void __init fsverity_init_bpf(void) | |
182 | { | |
183 | register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fsverity_set); | |
184 | } | |
185 | ||
186 | #endif /* CONFIG_BPF_SYSCALL */ |