Commit 6e083ab0 authored by Alexei Starovoitov's avatar Alexei Starovoitov
Browse files

Merge branch 'bpf-introduce-new-vfs-based-bpf-kfuncs' 

Matt Bobrowski says:

====================
bpf: introduce new VFS based BPF kfuncs

G'day!

A respin based off v3, which can be found here [0]. Original
motivations for introducing this suite of BPF kfuncs can be found here
[1].

The primary difference in this version of the patch series is that the
suite of VFS related BPF kfuncs added can be used from both sleepable
and non-sleepable BPF LSM program types. IOW, the KF_SLEEPABLE
annotation has been removed from all of them.

Changes sinve v3:

* KF_SLEEPABLE annotation has been dropped from all newly introduced
  VFS related BPF kfuncs. This includes bpf_get_task_exe_file(),
  bpf_put_file(), and bpf_path_d_path(). Both negative and positive
  selftests backing these new BPF kfuncs have also been updated
  accordingly.

* buf__sz conditional in bpf_path_d_path() has been updated from
  buf__sz <= 0, to !buf__sz.

* Syntax issues as reported so here [2] have been corrected.

[0] https://lore.kernel.org/bpf/20240726085604.2369469-1-mattbobrowski@google.com/
[1] https://lore.kernel.org/bpf/cover.1708377880.git.mattbobrowski@google.com/#t
[2] https://netdev.bots.linux.dev/static/nipa/874023/13742510/checkpatch/stdout
====================

Link: https://lore.kernel.org/r/20240731110833.1834742-1-mattbobrowski@google.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parents 3d650ab5 2b399b9b

fs/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -129,3 +129,4 @@ obj-$(CONFIG_EFIVAR_FS) += efivarfs/ 
obj-$(CONFIG_EROFS_FS)		+= erofs/

obj-$(CONFIG_VBOXSF_FS)		+= vboxsf/

obj-$(CONFIG_ZONEFS_FS)		+= zonefs/

obj-$(CONFIG_BPF_LSM)		+= bpf_fs_kfuncs.o

fs/bpf_fs_kfuncs.c

0 → 100644
+123 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

/* Copyright (c) 2024 Google LLC. */



#include <linux/bpf.h>

#include <linux/btf.h>

#include <linux/btf_ids.h>

#include <linux/dcache.h>

#include <linux/fs.h>

#include <linux/file.h>

#include <linux/mm.h>



__bpf_kfunc_start_defs();



/**

 * bpf_get_task_exe_file - get a reference on the exe_file struct file member of

 *                         the mm_struct that is nested within the supplied

 *                         task_struct

 * @task: task_struct of which the nested mm_struct exe_file member to get a

 * reference on

 *

 * Get a reference on the exe_file struct file member field of the mm_struct

 * nested within the supplied *task*. The referenced file pointer acquired by

 * this BPF kfunc must be released using bpf_put_file(). Failing to call

 * bpf_put_file() on the returned referenced struct file pointer that has been

 * acquired by this BPF kfunc will result in the BPF program being rejected by

 * the BPF verifier.

 *

 * This BPF kfunc may only be called from BPF LSM programs.

 *

 * Internally, this BPF kfunc leans on get_task_exe_file(), such that calling

 * bpf_get_task_exe_file() would be analogous to calling get_task_exe_file()

 * directly in kernel context.

 *

 * Return: A referenced struct file pointer to the exe_file member of the

 * mm_struct that is nested within the supplied *task*. On error, NULL is

 * returned.

 */

__bpf_kfunc struct file *bpf_get_task_exe_file(struct task_struct *task)

{

	return get_task_exe_file(task);

}



/**

 * bpf_put_file - put a reference on the supplied file

 * @file: file to put a reference on

 *

 * Put a reference on the supplied *file*. Only referenced file pointers may be

 * passed to this BPF kfunc. Attempting to pass an unreferenced file pointer, or

 * any other arbitrary pointer for that matter, will result in the BPF program

 * being rejected by the BPF verifier.

 *

 * This BPF kfunc may only be called from BPF LSM programs.

 */

__bpf_kfunc void bpf_put_file(struct file *file)

{

	fput(file);

}



/**

 * bpf_path_d_path - resolve the pathname for the supplied path

 * @path: path to resolve the pathname for

 * @buf: buffer to return the resolved pathname in

 * @buf__sz: length of the supplied buffer

 *

 * Resolve the pathname for the supplied *path* and store it in *buf*. This BPF

 * kfunc is the safer variant of the legacy bpf_d_path() helper and should be

 * used in place of bpf_d_path() whenever possible. It enforces KF_TRUSTED_ARGS

 * semantics, meaning that the supplied *path* must itself hold a valid

 * reference, or else the BPF program will be outright rejected by the BPF

 * verifier.

 *

 * This BPF kfunc may only be called from BPF LSM programs.

 *

 * Return: A positive integer corresponding to the length of the resolved

 * pathname in *buf*, including the NUL termination character. On error, a

 * negative integer is returned.

 */

__bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)

{

	int len;

	char *ret;



	if (!buf__sz)

		return -EINVAL;



	ret = d_path(path, buf, buf__sz);

	if (IS_ERR(ret))

		return PTR_ERR(ret);



	len = buf + buf__sz - ret;

	memmove(buf, ret, len);

	return len;

}



__bpf_kfunc_end_defs();



BTF_KFUNCS_START(bpf_fs_kfunc_set_ids)

BTF_ID_FLAGS(func, bpf_get_task_exe_file,

	     KF_ACQUIRE | KF_TRUSTED_ARGS | KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_put_file, KF_RELEASE)

BTF_ID_FLAGS(func, bpf_path_d_path, KF_TRUSTED_ARGS)

BTF_KFUNCS_END(bpf_fs_kfunc_set_ids)



static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)

{

	if (!btf_id_set8_contains(&bpf_fs_kfunc_set_ids, kfunc_id) ||

	    prog->type == BPF_PROG_TYPE_LSM)

		return 0;

	return -EACCES;

}



static const struct btf_kfunc_id_set bpf_fs_kfunc_set = {

	.owner = THIS_MODULE,

	.set = &bpf_fs_kfunc_set_ids,

	.filter = bpf_fs_kfuncs_filter,

};



static int __init bpf_fs_kfuncs_init(void)

{

	return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fs_kfunc_set);

}



late_initcall(bpf_fs_kfuncs_init);

tools/testing/selftests/bpf/bpf_experimental.h

+26 −0
Original line number Diff line number Diff line
@@ -195,6 +195,32 @@ extern void bpf_iter_task_vma_destroy(struct bpf_iter_task_vma *it) __ksym; 
 */

extern void bpf_throw(u64 cookie) __ksym;



/* Description

 *	Acquire a reference on the exe_file member field belonging to the

 *	mm_struct that is nested within the supplied task_struct. The supplied

 *	task_struct must be trusted/referenced.

 * Returns

 *	A referenced file pointer pointing to the exe_file member field of the

 *	mm_struct nested in the supplied task_struct, or NULL.

 */

extern struct file *bpf_get_task_exe_file(struct task_struct *task) __ksym;



/* Description

 *	Release a reference on the supplied file. The supplied file must be

 *	acquired.

 */

extern void bpf_put_file(struct file *file) __ksym;



/* Description

 *	Resolve a pathname for the supplied path and store it in the supplied

 *	buffer. The supplied path must be trusted/referenced.

 * Returns

 *	A positive integer corresponding to the length of the resolved pathname,

 *	including the NULL termination character, stored in the supplied

 *	buffer. On error, a negative integer is returned.

 */

extern int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz) __ksym;



/* This macro must be used to mark the exception callback corresponding to the

 * main program. For example:

 *

tools/testing/selftests/bpf/prog_tests/verifier.c

+4 −0
Original line number Diff line number Diff line
@@ -85,6 +85,8 @@ 
#include "verifier_value_or_null.skel.h"

#include "verifier_value_ptr_arith.skel.h"

#include "verifier_var_off.skel.h"

#include "verifier_vfs_accept.skel.h"

#include "verifier_vfs_reject.skel.h"

#include "verifier_xadd.skel.h"

#include "verifier_xdp.skel.h"

#include "verifier_xdp_direct_packet_access.skel.h"
@@ -205,6 +207,8 @@ void test_verifier_value(void) { RUN(verifier_value); } 
void test_verifier_value_illegal_alu(void)    { RUN(verifier_value_illegal_alu); }

void test_verifier_value_or_null(void)        { RUN(verifier_value_or_null); }

void test_verifier_var_off(void)              { RUN(verifier_var_off); }

void test_verifier_vfs_accept(void)	      { RUN(verifier_vfs_accept); }

void test_verifier_vfs_reject(void)	      { RUN(verifier_vfs_reject); }

void test_verifier_xadd(void)                 { RUN(verifier_xadd); }

void test_verifier_xdp(void)                  { RUN(verifier_xdp); }

void test_verifier_xdp_direct_packet_access(void) { RUN(verifier_xdp_direct_packet_access); }

tools/testing/selftests/bpf/progs/verifier_vfs_accept.c

0 → 100644
+85 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

/* Copyright (c) 2024 Google LLC. */



#include <vmlinux.h>

#include <bpf/bpf_helpers.h>

#include <bpf/bpf_tracing.h>



#include "bpf_misc.h"

#include "bpf_experimental.h"



static char buf[64];



SEC("lsm.s/file_open")

__success

int BPF_PROG(get_task_exe_file_and_put_kfunc_from_current_sleepable)

{

	struct file *acquired;



	acquired = bpf_get_task_exe_file(bpf_get_current_task_btf());

	if (!acquired)

		return 0;



	bpf_put_file(acquired);

	return 0;

}



SEC("lsm/file_open")

__success

int BPF_PROG(get_task_exe_file_and_put_kfunc_from_current_non_sleepable, struct file *file)

{

	struct file *acquired;



	acquired = bpf_get_task_exe_file(bpf_get_current_task_btf());

	if (!acquired)

		return 0;



	bpf_put_file(acquired);

	return 0;

}



SEC("lsm.s/task_alloc")

__success

int BPF_PROG(get_task_exe_file_and_put_kfunc_from_argument,

	     struct task_struct *task)

{

	struct file *acquired;



	acquired = bpf_get_task_exe_file(task);

	if (!acquired)

		return 0;



	bpf_put_file(acquired);

	return 0;

}



SEC("lsm.s/inode_getattr")

__success

int BPF_PROG(path_d_path_from_path_argument, struct path *path)

{

	int ret;



	ret = bpf_path_d_path(path, buf, sizeof(buf));

	__sink(ret);

	return 0;

}



SEC("lsm.s/file_open")

__success

int BPF_PROG(path_d_path_from_file_argument, struct file *file)

{

	int ret;

	struct path *path;



	/* The f_path member is a path which is embedded directly within a

	 * file. Therefore, a pointer to such embedded members are still

	 * recognized by the BPF verifier as being PTR_TRUSTED as it's

	 * essentially PTR_TRUSTED w/ a non-zero fixed offset.

	 */

	path = &file->f_path;

	ret = bpf_path_d_path(path, buf, sizeof(buf));

	__sink(ret);

	return 0;

}



char _license[] SEC("license") = "GPL";