1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Ioctl to get a verity file's digest
4 *
5 * Copyright 2019 Google LLC
6 */
7
8#include "fsverity_private.h"
9
10#include <linux/bpf.h>
11#include <linux/btf.h>
12#include <linux/uaccess.h>
13
14/**
15 * fsverity_ioctl_measure() - get a verity file's digest
16 * @filp: file to get digest of
17 * @_uarg: user pointer to fsverity_digest
18 *
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
21 * Documentation/filesystems/fsverity.rst for the documentation.
22 *
23 * Return: 0 on success, -errno on failure
24 */
25int 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
56	if (copy_to_user(uarg->digest, vi->file_digest, hash_alg->digest_size))
57		return -EFAULT;
58
59	return 0;
60}
61EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
62
63/**
64 * fsverity_get_digest() - get a verity file's digest
65 * @inode: inode to get digest of
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
69 *
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.
73 *
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.
84 */
85int fsverity_get_digest(struct inode *inode,
86			u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
87			u8 *alg, enum hash_algo *halg)
88{
89	const struct fsverity_info *vi;
90	const struct fsverity_hash_alg *hash_alg;
91
92	vi = fsverity_get_info(inode);
93	if (!vi)
94		return 0; /* not a verity file */
95
96	hash_alg = vi->tree_params.hash_alg;
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;
103}
104EXPORT_SYMBOL_GPL(fsverity_get_digest);
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
162BTF_KFUNCS_START(fsverity_set_ids)
163BTF_ID_FLAGS(func, bpf_get_fsverity_digest, KF_TRUSTED_ARGS)
164BTF_KFUNCS_END(fsverity_set_ids)
165
166static 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
175static 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
181void __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 */
187