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author | Song Liu <song@kernel.org> | 2023-11-29 15:44:13 -0800 |
---|---|---|
committer | Alexei Starovoitov <ast@kernel.org> | 2023-12-01 16:21:03 -0800 |
commit | 67814c00de3161181cddd06c77aeaf86ac4cc584 (patch) | |
tree | ec467b83873691b94b7e4ded55a4abdfa46ef41c | |
parent | ac9c05e0e453cfcab2866f6d28f257590e4f66e5 (diff) | |
download | linux-67814c00de3161181cddd06c77aeaf86ac4cc584.tar.gz linux-67814c00de3161181cddd06c77aeaf86ac4cc584.tar.bz2 linux-67814c00de3161181cddd06c77aeaf86ac4cc584.zip |
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>
-rw-r--r-- | fs/verity/fsverity_private.h | 10 | ||||
-rw-r--r-- | fs/verity/init.c | 1 | ||||
-rw-r--r-- | fs/verity/measure.c | 84 |
3 files changed, 95 insertions, 0 deletions
diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h index d071a6e32581..a6a6b2749241 100644 --- a/fs/verity/fsverity_private.h +++ b/fs/verity/fsverity_private.h @@ -100,6 +100,16 @@ fsverity_msg(const struct inode *inode, const char *level, #define fsverity_err(inode, fmt, ...) \ fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__) +/* measure.c */ + +#ifdef CONFIG_BPF_SYSCALL +void __init fsverity_init_bpf(void); +#else +static inline void fsverity_init_bpf(void) +{ +} +#endif + /* open.c */ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params, diff --git a/fs/verity/init.c b/fs/verity/init.c index a29f062f6047..1e207c0f71de 100644 --- a/fs/verity/init.c +++ b/fs/verity/init.c @@ -69,6 +69,7 @@ static int __init fsverity_init(void) fsverity_init_workqueue(); fsverity_init_sysctl(); fsverity_init_signature(); + fsverity_init_bpf(); return 0; } late_initcall(fsverity_init) diff --git a/fs/verity/measure.c b/fs/verity/measure.c index eec5956141da..bf7a5f4cccaf 100644 --- a/fs/verity/measure.c +++ b/fs/verity/measure.c @@ -7,6 +7,8 @@ #include "fsverity_private.h" +#include <linux/bpf.h> +#include <linux/btf.h> #include <linux/uaccess.h> /** @@ -100,3 +102,85 @@ int fsverity_get_digest(struct inode *inode, return hash_alg->digest_size; } EXPORT_SYMBOL_GPL(fsverity_get_digest); + +#ifdef CONFIG_BPF_SYSCALL + +/* bpf kfuncs */ +__bpf_kfunc_start_defs(); + +/** + * bpf_get_fsverity_digest: read fsverity digest of file + * @file: file to get digest from + * @digest_ptr: (out) dynptr for struct fsverity_digest + * + * Read fsverity_digest of *file* into *digest_ptr*. + * + * Return: 0 on success, a negative value on error. + */ +__bpf_kfunc int bpf_get_fsverity_digest(struct file *file, struct bpf_dynptr_kern *digest_ptr) +{ + const struct inode *inode = file_inode(file); + u32 dynptr_sz = __bpf_dynptr_size(digest_ptr); + struct fsverity_digest *arg; + const struct fsverity_info *vi; + const struct fsverity_hash_alg *hash_alg; + int out_digest_sz; + + if (dynptr_sz < sizeof(struct fsverity_digest)) + return -EINVAL; + + arg = __bpf_dynptr_data_rw(digest_ptr, dynptr_sz); + if (!arg) + return -EINVAL; + + if (!IS_ALIGNED((uintptr_t)arg, __alignof__(*arg))) + return -EINVAL; + + vi = fsverity_get_info(inode); + if (!vi) + return -ENODATA; /* not a verity file */ + + hash_alg = vi->tree_params.hash_alg; + + arg->digest_algorithm = hash_alg - fsverity_hash_algs; + arg->digest_size = hash_alg->digest_size; + + out_digest_sz = dynptr_sz - sizeof(struct fsverity_digest); + + /* copy digest */ + memcpy(arg->digest, vi->file_digest, min_t(int, hash_alg->digest_size, out_digest_sz)); + + /* fill the extra buffer with zeros */ + if (out_digest_sz > hash_alg->digest_size) + memset(arg->digest + arg->digest_size, 0, out_digest_sz - hash_alg->digest_size); + + return 0; +} + +__bpf_kfunc_end_defs(); + +BTF_SET8_START(fsverity_set_ids) +BTF_ID_FLAGS(func, bpf_get_fsverity_digest, KF_TRUSTED_ARGS) +BTF_SET8_END(fsverity_set_ids) + +static int bpf_get_fsverity_digest_filter(const struct bpf_prog *prog, u32 kfunc_id) +{ + if (!btf_id_set8_contains(&fsverity_set_ids, kfunc_id)) + return 0; + + /* Only allow to attach from LSM hooks, to avoid recursion */ + return prog->type != BPF_PROG_TYPE_LSM ? -EACCES : 0; +} + +static const struct btf_kfunc_id_set bpf_fsverity_set = { + .owner = THIS_MODULE, + .set = &fsverity_set_ids, + .filter = bpf_get_fsverity_digest_filter, +}; + +void __init fsverity_init_bpf(void) +{ + register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fsverity_set); +} + +#endif /* CONFIG_BPF_SYSCALL */ |