Commit 3f6719c7 authored by KP Singh's avatar KP Singh Committed by Daniel Borkmann
Browse files

bpf: Add bpf_bprm_opts_set helper 



The helper allows modification of certain bits on the linux_binprm
struct starting with the secureexec bit which can be updated using the
BPF_F_BPRM_SECUREEXEC flag.

secureexec can be set by the LSM for privilege gaining executions to set
the AT_SECURE auxv for glibc.  When set, the dynamic linker disables the
use of certain environment variables (like LD_PRELOAD).

Signed-off-by: default avatarKP Singh <kpsingh@google.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarMartin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20201117232929.2156341-1-kpsingh@chromium.org
parent cbf398d7

include/uapi/linux/bpf.h

+16 −0
Original line number Diff line number Diff line
@@ -3787,6 +3787,16 @@ union bpf_attr { 
 *		*ARG_PTR_TO_BTF_ID* of type *task_struct*.

 *	Return

 *		Pointer to the current task.

 *

 * long bpf_bprm_opts_set(struct linux_binprm *bprm, u64 flags)

 *	Description

 *		Set or clear certain options on *bprm*:

 *

 *		**BPF_F_BPRM_SECUREEXEC** Set the secureexec bit

 *		which sets the **AT_SECURE** auxv for glibc. The bit

 *		is cleared if the flag is not specified.

 *	Return

 *		**-EINVAL** if invalid *flags* are passed, zero otherwise.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -3948,6 +3958,7 @@ union bpf_attr { 
	FN(task_storage_get),		\

	FN(task_storage_delete),	\

	FN(get_current_task_btf),	\

	FN(bprm_opts_set),		\

	/* */



/* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -4119,6 +4130,11 @@ enum bpf_lwt_encap_mode { 
	BPF_LWT_ENCAP_IP,

};



/* Flags for bpf_bprm_opts_set helper */

enum {

	BPF_F_BPRM_SECUREEXEC	= (1ULL << 0),

};



#define __bpf_md_ptr(type, name)	\

union {					\

	type name;			\

kernel/bpf/bpf_lsm.c

+26 −0
Original line number Diff line number Diff line
@@ -7,6 +7,7 @@ 
#include <linux/filter.h>

#include <linux/bpf.h>

#include <linux/btf.h>

#include <linux/binfmts.h>

#include <linux/lsm_hooks.h>

#include <linux/bpf_lsm.h>

#include <linux/kallsyms.h>
@@ -51,6 +52,29 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, 
	return 0;

}



/* Mask for all the currently supported BPRM option flags */

#define BPF_F_BRPM_OPTS_MASK	BPF_F_BPRM_SECUREEXEC



BPF_CALL_2(bpf_bprm_opts_set, struct linux_binprm *, bprm, u64, flags)

{

	if (flags & ~BPF_F_BRPM_OPTS_MASK)

		return -EINVAL;



	bprm->secureexec = (flags & BPF_F_BPRM_SECUREEXEC);

	return 0;

}



BTF_ID_LIST_SINGLE(bpf_bprm_opts_set_btf_ids, struct, linux_binprm)



const static struct bpf_func_proto bpf_bprm_opts_set_proto = {

	.func		= bpf_bprm_opts_set,

	.gpl_only	= false,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_BTF_ID,

	.arg1_btf_id	= &bpf_bprm_opts_set_btf_ids[0],

	.arg2_type	= ARG_ANYTHING,

};



static const struct bpf_func_proto *

bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)

{
@@ -71,6 +95,8 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
		return &bpf_task_storage_get_proto;

	case BPF_FUNC_task_storage_delete:

		return &bpf_task_storage_delete_proto;

	case BPF_FUNC_bprm_opts_set:

		return &bpf_bprm_opts_set_proto;

	default:

		return tracing_prog_func_proto(func_id, prog);

	}

scripts/bpf_helpers_doc.py

+2 −0
Original line number Diff line number Diff line
@@ -418,6 +418,7 @@ class PrinterHelpers(Printer): 
            'struct bpf_tcp_sock',

            'struct bpf_tunnel_key',

            'struct bpf_xfrm_state',

            'struct linux_binprm',

            'struct pt_regs',

            'struct sk_reuseport_md',

            'struct sockaddr',
@@ -465,6 +466,7 @@ class PrinterHelpers(Printer): 
            'struct bpf_tcp_sock',

            'struct bpf_tunnel_key',

            'struct bpf_xfrm_state',

            'struct linux_binprm',

            'struct pt_regs',

            'struct sk_reuseport_md',

            'struct sockaddr',

tools/include/uapi/linux/bpf.h

+16 −0
Original line number Diff line number Diff line
@@ -3787,6 +3787,16 @@ union bpf_attr { 
 *		*ARG_PTR_TO_BTF_ID* of type *task_struct*.

 *	Return

 *		Pointer to the current task.

 *

 * long bpf_bprm_opts_set(struct linux_binprm *bprm, u64 flags)

 *	Description

 *		Set or clear certain options on *bprm*:

 *

 *		**BPF_F_BPRM_SECUREEXEC** Set the secureexec bit

 *		which sets the **AT_SECURE** auxv for glibc. The bit

 *		is cleared if the flag is not specified.

 *	Return

 *		**-EINVAL** if invalid *flags* are passed, zero otherwise.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -3948,6 +3958,7 @@ union bpf_attr { 
	FN(task_storage_get),		\

	FN(task_storage_delete),	\

	FN(get_current_task_btf),	\

	FN(bprm_opts_set),		\

	/* */



/* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -4119,6 +4130,11 @@ enum bpf_lwt_encap_mode { 
	BPF_LWT_ENCAP_IP,

};



/* Flags for bpf_bprm_opts_set helper */

enum {

	BPF_F_BPRM_SECUREEXEC	= (1ULL << 0),

};



#define __bpf_md_ptr(type, name)	\

union {					\

	type name;			\

CRA Git | Maintained and supported by SUSTech CRA and CCSE