Commit 9b99edca authored by Jiri Olsa's avatar Jiri Olsa Committed by Alexei Starovoitov
Browse files

bpf: Add bpf_get_func_ip helper for tracing programs 



Adding bpf_get_func_ip helper for BPF_PROG_TYPE_TRACING programs,
specifically for all trampoline attach types.

The trampoline's caller IP address is stored in (ctx - 8) address.
so there's no reason to actually call the helper, but rather fixup
the call instruction and return [ctx - 8] value directly.

Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210714094400.396467-4-jolsa@kernel.org
parent 1e37392c

include/uapi/linux/bpf.h

+7 −0
Original line number Diff line number Diff line
@@ -4841,6 +4841,12 @@ union bpf_attr { 
 *		**-EINVAL** if *timer* was not initialized with bpf_timer_init() earlier.

 *		**-EDEADLK** if callback_fn tried to call bpf_timer_cancel() on its

 *		own timer which would have led to a deadlock otherwise.

 *

 * u64 bpf_get_func_ip(void *ctx)

 * 	Description

 * 		Get address of the traced function (for tracing programs).

 * 	Return

 * 		Address of the traced function.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -5016,6 +5022,7 @@ union bpf_attr { 
	FN(timer_set_callback),		\

	FN(timer_start),		\

	FN(timer_cancel),		\

	FN(get_func_ip),		\

	/* */



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

kernel/bpf/verifier.c

+43 −0
Original line number Diff line number Diff line
@@ -6161,6 +6161,27 @@ static int check_bpf_snprintf_call(struct bpf_verifier_env *env, 
	return err;

}



static int check_get_func_ip(struct bpf_verifier_env *env)

{

	enum bpf_attach_type eatype = env->prog->expected_attach_type;

	enum bpf_prog_type type = resolve_prog_type(env->prog);

	int func_id = BPF_FUNC_get_func_ip;



	if (type == BPF_PROG_TYPE_TRACING) {

		if (eatype != BPF_TRACE_FENTRY && eatype != BPF_TRACE_FEXIT &&

		    eatype != BPF_MODIFY_RETURN) {

			verbose(env, "func %s#%d supported only for fentry/fexit/fmod_ret programs\n",

				func_id_name(func_id), func_id);

			return -ENOTSUPP;

		}

		return 0;

	}



	verbose(env, "func %s#%d not supported for program type %d\n",

		func_id_name(func_id), func_id, type);

	return -ENOTSUPP;

}



static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,

			     int *insn_idx_p)

{
@@ -6439,6 +6460,12 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn 
	if (func_id == BPF_FUNC_get_stackid || func_id == BPF_FUNC_get_stack)

		env->prog->call_get_stack = true;



	if (func_id == BPF_FUNC_get_func_ip) {

		if (check_get_func_ip(env))

			return -ENOTSUPP;

		env->prog->call_get_func_ip = true;

	}



	if (changes_data)

		clear_all_pkt_pointers(env);

	return 0;
@@ -12632,6 +12659,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env) 
{

	struct bpf_prog *prog = env->prog;

	bool expect_blinding = bpf_jit_blinding_enabled(prog);

	enum bpf_prog_type prog_type = resolve_prog_type(prog);

	struct bpf_insn *insn = prog->insnsi;

	const struct bpf_func_proto *fn;

	const int insn_cnt = prog->len;
@@ -12998,6 +13026,21 @@ static int do_misc_fixups(struct bpf_verifier_env *env) 
			continue;

		}



		/* Implement bpf_get_func_ip inline. */

		if (prog_type == BPF_PROG_TYPE_TRACING &&

		    insn->imm == BPF_FUNC_get_func_ip) {

			/* Load IP address from ctx - 8 */

			insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);



			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, 1);

			if (!new_prog)

				return -ENOMEM;



			env->prog = prog = new_prog;

			insn      = new_prog->insnsi + i + delta;

			continue;

		}



patch_call_imm:

		fn = env->ops->get_func_proto(insn->imm, env->prog);

		/* all functions that have prototype and verifier allowed

kernel/trace/bpf_trace.c

+15 −0
Original line number Diff line number Diff line
@@ -948,6 +948,19 @@ const struct bpf_func_proto bpf_snprintf_btf_proto = { 
	.arg5_type	= ARG_ANYTHING,

};



BPF_CALL_1(bpf_get_func_ip_tracing, void *, ctx)

{

	/* This helper call is inlined by verifier. */

	return ((u64 *)ctx)[-1];

}



static const struct bpf_func_proto bpf_get_func_ip_proto_tracing = {

	.func		= bpf_get_func_ip_tracing,

	.gpl_only	= true,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_CTX,

};



const struct bpf_func_proto *

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

{
@@ -1058,6 +1071,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
		return &bpf_for_each_map_elem_proto;

	case BPF_FUNC_snprintf:

		return &bpf_snprintf_proto;

	case BPF_FUNC_get_func_ip:

		return &bpf_get_func_ip_proto_tracing;

	default:

		return bpf_base_func_proto(func_id);

	}

tools/include/uapi/linux/bpf.h

+7 −0
Original line number Diff line number Diff line
@@ -4841,6 +4841,12 @@ union bpf_attr { 
 *		**-EINVAL** if *timer* was not initialized with bpf_timer_init() earlier.

 *		**-EDEADLK** if callback_fn tried to call bpf_timer_cancel() on its

 *		own timer which would have led to a deadlock otherwise.

 *

 * u64 bpf_get_func_ip(void *ctx)

 * 	Description

 * 		Get address of the traced function (for tracing programs).

 * 	Return

 * 		Address of the traced function.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -5016,6 +5022,7 @@ union bpf_attr { 
	FN(timer_set_callback),		\

	FN(timer_start),		\

	FN(timer_cancel),		\

	FN(get_func_ip),		\

	/* */



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