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 */ 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 56 if (copy_to_user(uarg->digest, vi->file_digest, hash_alg->digest_size)) 57 return -EFAULT; 58 59 return 0; 60 } 61 EXPORT_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 */ 85 int 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 } 104 EXPORT_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_p: (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 *digest_p) 121 { 122 struct bpf_dynptr_kern *digest_ptr = (struct bpf_dynptr_kern *)digest_p; 123 const struct inode *inode = file_inode(file); 124 u32 dynptr_sz = __bpf_dynptr_size(digest_ptr); 125 struct fsverity_digest *arg; 126 const struct fsverity_info *vi; 127 const struct fsverity_hash_alg *hash_alg; 128 int out_digest_sz; 129 130 if (dynptr_sz < sizeof(struct fsverity_digest)) 131 return -EINVAL; 132 133 arg = __bpf_dynptr_data_rw(digest_ptr, dynptr_sz); 134 if (!arg) 135 return -EINVAL; 136 137 if (!IS_ALIGNED((uintptr_t)arg, __alignof__(*arg))) 138 return -EINVAL; 139 140 vi = fsverity_get_info(inode); 141 if (!vi) 142 return -ENODATA; /* not a verity file */ 143 144 hash_alg = vi->tree_params.hash_alg; 145 146 arg->digest_algorithm = hash_alg - fsverity_hash_algs; 147 arg->digest_size = hash_alg->digest_size; 148 149 out_digest_sz = dynptr_sz - sizeof(struct fsverity_digest); 150 151 /* copy digest */ 152 memcpy(arg->digest, vi->file_digest, min_t(int, hash_alg->digest_size, out_digest_sz)); 153 154 /* fill the extra buffer with zeros */ 155 if (out_digest_sz > hash_alg->digest_size) 156 memset(arg->digest + arg->digest_size, 0, out_digest_sz - hash_alg->digest_size); 157 158 return 0; 159 } 160 161 __bpf_kfunc_end_defs(); 162 163 BTF_KFUNCS_START(fsverity_set_ids) 164 BTF_ID_FLAGS(func, bpf_get_fsverity_digest, KF_TRUSTED_ARGS) 165 BTF_KFUNCS_END(fsverity_set_ids) 166 167 static int bpf_get_fsverity_digest_filter(const struct bpf_prog *prog, u32 kfunc_id) 168 { 169 if (!btf_id_set8_contains(&fsverity_set_ids, kfunc_id)) 170 return 0; 171 172 /* Only allow to attach from LSM hooks, to avoid recursion */ 173 return prog->type != BPF_PROG_TYPE_LSM ? -EACCES : 0; 174 } 175 176 static const struct btf_kfunc_id_set bpf_fsverity_set = { 177 .owner = THIS_MODULE, 178 .set = &fsverity_set_ids, 179 .filter = bpf_get_fsverity_digest_filter, 180 }; 181 182 void __init fsverity_init_bpf(void) 183 { 184 register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fsverity_set); 185 } 186 187 #endif /* CONFIG_BPF_SYSCALL */ 188