Commit 67814c00 authored by Song Liu's avatar Song Liu Committed by Alexei Starovoitov
Browse files

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: default avatarSong Liu <song@kernel.org>
Acked-by: default avatarEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20231129234417.856536-3-song@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent ac9c05e0

fs/verity/fsverity_private.h

+10 −0
Original line number Diff line number Diff line
@@ -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,

fs/verity/init.c

+1 −0
Original line number Diff line number Diff line
@@ -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)

fs/verity/measure.c

+84 −0
Original line number Diff line number Diff line
@@ -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 */