Commit d6aef08a authored by Kumar Kartikeya Dwivedi's avatar Kumar Kartikeya Dwivedi Committed by Alexei Starovoitov
Browse files

bpf: Add bpf_kallsyms_lookup_name helper 



This helper allows us to get the address of a kernel symbol from inside
a BPF_PROG_TYPE_SYSCALL prog (used by gen_loader), so that we can
relocate typeless ksym vars.

Signed-off-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20211028063501.2239335-2-memxor@gmail.com
parent 2895f48f

include/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -2110,6 +2110,7 @@ extern const struct bpf_func_proto bpf_for_each_map_elem_proto; 
extern const struct bpf_func_proto bpf_btf_find_by_name_kind_proto;

extern const struct bpf_func_proto bpf_sk_setsockopt_proto;

extern const struct bpf_func_proto bpf_sk_getsockopt_proto;

extern const struct bpf_func_proto bpf_kallsyms_lookup_name_proto;



const struct bpf_func_proto *tracing_prog_func_proto(

  enum bpf_func_id func_id, const struct bpf_prog *prog);

include/uapi/linux/bpf.h

+16 −0
Original line number Diff line number Diff line
@@ -4923,6 +4923,21 @@ union bpf_attr { 
 *		Dynamically cast a *sk* pointer to a *unix_sock* pointer.

 *	Return

 *		*sk* if casting is valid, or **NULL** otherwise.

 *

 * long bpf_kallsyms_lookup_name(const char *name, int name_sz, int flags, u64 *res)

 *	Description

 *		Get the address of a kernel symbol, returned in *res*. *res* is

 *		set to 0 if the symbol is not found.

 *	Return

 *		On success, zero. On error, a negative value.

 *

 *		**-EINVAL** if *flags* is not zero.

 *

 *		**-EINVAL** if string *name* is not the same size as *name_sz*.

 *

 *		**-ENOENT** if symbol is not found.

 *

 *		**-EPERM** if caller does not have permission to obtain kernel address.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -5104,6 +5119,7 @@ union bpf_attr { 
	FN(get_branch_snapshot),	\

	FN(trace_vprintk),		\

	FN(skc_to_unix_sock),		\

	FN(kallsyms_lookup_name),	\

	/* */



/* integer value in 'imm' field of BPF_CALL instruction selects which helper

kernel/bpf/syscall.c

+27 −0
Original line number Diff line number Diff line
@@ -4781,6 +4781,31 @@ static const struct bpf_func_proto bpf_sys_close_proto = { 
	.arg1_type	= ARG_ANYTHING,

};



BPF_CALL_4(bpf_kallsyms_lookup_name, const char *, name, int, name_sz, int, flags, u64 *, res)

{

	if (flags)

		return -EINVAL;



	if (name_sz <= 1 || name[name_sz - 1])

		return -EINVAL;



	if (!bpf_dump_raw_ok(current_cred()))

		return -EPERM;



	*res = kallsyms_lookup_name(name);

	return *res ? 0 : -ENOENT;

}



const struct bpf_func_proto bpf_kallsyms_lookup_name_proto = {

	.func		= bpf_kallsyms_lookup_name,

	.gpl_only	= false,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_MEM,

	.arg2_type	= ARG_CONST_SIZE,

	.arg3_type	= ARG_ANYTHING,

	.arg4_type	= ARG_PTR_TO_LONG,

};



static const struct bpf_func_proto *

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

{
@@ -4791,6 +4816,8 @@ syscall_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
		return &bpf_btf_find_by_name_kind_proto;

	case BPF_FUNC_sys_close:

		return &bpf_sys_close_proto;

	case BPF_FUNC_kallsyms_lookup_name:

		return &bpf_kallsyms_lookup_name_proto;

	default:

		return tracing_prog_func_proto(func_id, prog);

	}

tools/include/uapi/linux/bpf.h

+16 −0
Original line number Diff line number Diff line
@@ -4923,6 +4923,21 @@ union bpf_attr { 
 *		Dynamically cast a *sk* pointer to a *unix_sock* pointer.

 *	Return

 *		*sk* if casting is valid, or **NULL** otherwise.

 *

 * long bpf_kallsyms_lookup_name(const char *name, int name_sz, int flags, u64 *res)

 *	Description

 *		Get the address of a kernel symbol, returned in *res*. *res* is

 *		set to 0 if the symbol is not found.

 *	Return

 *		On success, zero. On error, a negative value.

 *

 *		**-EINVAL** if *flags* is not zero.

 *

 *		**-EINVAL** if string *name* is not the same size as *name_sz*.

 *

 *		**-ENOENT** if symbol is not found.

 *

 *		**-EPERM** if caller does not have permission to obtain kernel address.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -5104,6 +5119,7 @@ union bpf_attr { 
	FN(get_branch_snapshot),	\

	FN(trace_vprintk),		\

	FN(skc_to_unix_sock),		\

	FN(kallsyms_lookup_name),	\

	/* */



/* integer value in 'imm' field of BPF_CALL instruction selects which helper