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1// SPDX-License-Identifier: GPL-2.02/*3 * Ioctl to get a verity file's digest4 *5 * Copyright 2019 Google LLC6 */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 digest16 * @filp: file to get digest of17 * @_uarg: user pointer to fsverity_digest18 *19 * Retrieve the file digest that the kernel is enforcing for reads from a verity20 * file. See the "FS_IOC_MEASURE_VERITY" section of21 * Documentation/filesystems/fsverity.rst for the documentation.22 *23 * Return: 0 on success, -errno on failure24 */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 can40 * return the digest if it fits in the available space. We write back41 * 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 digest65 * @inode: inode to get digest of66 * @raw_digest: (out) the raw file digest67 * @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value68 * @halg: (out) the digest's algorithm, as a HASH_ALGO_* value69 *70 * Retrieves the fsverity digest of the given file. The file must have been71 * 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 either75 * @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, since78 * @raw_digest is meaningless without knowing which algorithm it uses! fsverity79 * provides no security guarantee for users who ignore the algorithm ID, even if80 * 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 have83 * 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_SYSCALL107 108/* bpf kfuncs */109__bpf_kfunc_start_defs();110 111/**112 * bpf_get_fsverity_digest: read fsverity digest of file113 * @file: file to get digest from114 * @digest_p: (out) dynptr for struct fsverity_digest115 *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 163BTF_KFUNCS_START(fsverity_set_ids)164BTF_ID_FLAGS(func, bpf_get_fsverity_digest, KF_TRUSTED_ARGS)165BTF_KFUNCS_END(fsverity_set_ids)166 167static 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 176static 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 182void __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