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bpf, fsverity: Add kfunc bpf_get_fsverity_digest
fsverity provides fast and reliable hash of files, namely fsverity_digest. The digest can be used by security solutions to verify file contents. Add new kfunc bpf_get_fsverity_digest() so that we can access fsverity from BPF LSM programs. This kfunc is added to fs/verity/measure.c because some data structure used in the function is private to fsverity (fs/verity/fsverity_private.h). To avoid recursion, bpf_get_fsverity_digest is only allowed in BPF LSM programs. Signed-off-by: Song Liu <song@kernel.org> Acked-by: Eric Biggers <ebiggers@google.com> Link: https://lore.kernel.org/r/20231129234417.856536-3-song@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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@ -100,6 +100,16 @@ fsverity_msg(const struct inode *inode, const char *level,
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#define fsverity_err(inode, fmt, ...) \
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fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
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/* measure.c */
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#ifdef CONFIG_BPF_SYSCALL
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void __init fsverity_init_bpf(void);
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#else
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static inline void fsverity_init_bpf(void)
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{
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}
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#endif
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/* open.c */
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int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
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@ -69,6 +69,7 @@ static int __init fsverity_init(void)
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fsverity_init_workqueue();
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fsverity_init_sysctl();
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fsverity_init_signature();
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fsverity_init_bpf();
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return 0;
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}
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late_initcall(fsverity_init)
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@ -7,6 +7,8 @@
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#include "fsverity_private.h"
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#include <linux/bpf.h>
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#include <linux/btf.h>
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#include <linux/uaccess.h>
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/**
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@ -100,3 +102,85 @@ int fsverity_get_digest(struct inode *inode,
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return hash_alg->digest_size;
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}
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EXPORT_SYMBOL_GPL(fsverity_get_digest);
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#ifdef CONFIG_BPF_SYSCALL
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/* bpf kfuncs */
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__bpf_kfunc_start_defs();
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/**
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* bpf_get_fsverity_digest: read fsverity digest of file
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* @file: file to get digest from
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* @digest_ptr: (out) dynptr for struct fsverity_digest
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*
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* Read fsverity_digest of *file* into *digest_ptr*.
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*
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* Return: 0 on success, a negative value on error.
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*/
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__bpf_kfunc int bpf_get_fsverity_digest(struct file *file, struct bpf_dynptr_kern *digest_ptr)
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{
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const struct inode *inode = file_inode(file);
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u32 dynptr_sz = __bpf_dynptr_size(digest_ptr);
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struct fsverity_digest *arg;
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const struct fsverity_info *vi;
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const struct fsverity_hash_alg *hash_alg;
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int out_digest_sz;
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if (dynptr_sz < sizeof(struct fsverity_digest))
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return -EINVAL;
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arg = __bpf_dynptr_data_rw(digest_ptr, dynptr_sz);
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if (!arg)
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return -EINVAL;
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if (!IS_ALIGNED((uintptr_t)arg, __alignof__(*arg)))
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return -EINVAL;
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vi = fsverity_get_info(inode);
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if (!vi)
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return -ENODATA; /* not a verity file */
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hash_alg = vi->tree_params.hash_alg;
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arg->digest_algorithm = hash_alg - fsverity_hash_algs;
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arg->digest_size = hash_alg->digest_size;
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out_digest_sz = dynptr_sz - sizeof(struct fsverity_digest);
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/* copy digest */
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memcpy(arg->digest, vi->file_digest, min_t(int, hash_alg->digest_size, out_digest_sz));
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/* fill the extra buffer with zeros */
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if (out_digest_sz > hash_alg->digest_size)
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memset(arg->digest + arg->digest_size, 0, out_digest_sz - hash_alg->digest_size);
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return 0;
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}
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__bpf_kfunc_end_defs();
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BTF_SET8_START(fsverity_set_ids)
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BTF_ID_FLAGS(func, bpf_get_fsverity_digest, KF_TRUSTED_ARGS)
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BTF_SET8_END(fsverity_set_ids)
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static int bpf_get_fsverity_digest_filter(const struct bpf_prog *prog, u32 kfunc_id)
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{
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if (!btf_id_set8_contains(&fsverity_set_ids, kfunc_id))
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return 0;
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/* Only allow to attach from LSM hooks, to avoid recursion */
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return prog->type != BPF_PROG_TYPE_LSM ? -EACCES : 0;
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}
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static const struct btf_kfunc_id_set bpf_fsverity_set = {
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.owner = THIS_MODULE,
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.set = &fsverity_set_ids,
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.filter = bpf_get_fsverity_digest_filter,
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};
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void __init fsverity_init_bpf(void)
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{
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register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fsverity_set);
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}
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#endif /* CONFIG_BPF_SYSCALL */
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