linux-kernel - Re: [PATCH bpf-next 1/2] bpf: support bpf_get_func_arg() for BPF_TRACE_RAW

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Message-Id: <bf8e99a4398ad6c1383a82fd33fa1e0cfdfc6b935c8d4d8f5216a64cafccb660@mail.kernel.org>
Date: Fri, 16 Jan 2026 04:20:19 +0000 (UTC)
From: bot+bpf-ci@...nel.org
To: menglong8.dong@...il.com,ast@...nel.org
Cc: daniel@...earbox.net,john.fastabend@...il.com,andrii@...nel.org,martin.lau@...ux.dev,eddyz87@...il.com,song@...nel.org,yonghong.song@...ux.dev,kpsingh@...nel.org,sdf@...ichev.me,haoluo@...gle.com,jolsa@...nel.org,mattbobrowski@...gle.com,rostedt@...dmis.org,mhiramat@...nel.org,mathieu.desnoyers@...icios.com,bpf@...r.kernel.org,linux-kernel@...r.kernel.org,linux-trace-kernel@...r.kernel.org,ast@...nel.org,andrii@...nel.org,daniel@...earbox.net,martin.lau@...nel.org,eddyz87@...il.com,yonghong.song@...ux.dev,clm@...a.com,ihor.solodrai@...ux.dev
Subject: Re: [PATCH bpf-next 1/2] bpf: support bpf_get_func_arg() for BPF_TRACE_RAW_TP

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 7a375f608263..223e5b483bbd 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -23321,8 +23321,18 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
>  		/* Implement bpf_get_func_arg inline. */
>  		if (prog_type == BPF_PROG_TYPE_TRACING &&
>  		    insn->imm == BPF_FUNC_get_func_arg) {
> +			if (eatype == BPF_TRACE_RAW_TP) {
> +				int nr_args;
> +
> +				if (!prog->aux->attach_func_proto)
> +					return -EINVAL;
> +				nr_args = btf_type_vlen(prog->aux->attach_func_proto);
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The attach_func_proto for raw tracepoints points to the BTF func_proto of
__bpf_trace_* or btf_trace_* which has an extra "void *__data" as the
first parameter. For example, a tracepoint declared with TP_PROTO(int a)
results in a btf_trace_* typedef of "void (*)(void *__data, int a)" which
has 2 parameters.

Does btf_type_vlen() return the count including the hidden __data param?
If so, a tracepoint with 1 actual argument would report nr_args=2, but
the BPF context only contains 1 argument. Calling bpf_get_func_arg(ctx, 1)
would pass the bounds check (1 < 2) but read out of bounds from ctx.

The bpf_trace_run* functions populate args[] with only the actual
tracepoint arguments (see __bpf_trace_run() in kernel/trace/bpf_trace.c),
not including __data. Should nr_args be adjusted by subtracting 1 to
account for the hidden first parameter?

> +				/* Save nr_args to reg0 */
> +				insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, nr_args);
> +			} else {
> +				/* Load nr_args from ctx - 8 */
> +				insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
> +			}

[ ... ]

> @@ -23374,8 +23384,18 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
>  		/* Implement get_func_arg_cnt inline. */
>  		if (prog_type == BPF_PROG_TYPE_TRACING &&
>  		    insn->imm == BPF_FUNC_get_func_arg_cnt) {
> +			if (eatype == BPF_TRACE_RAW_TP) {
> +				int nr_args;
> +
> +				if (!prog->aux->attach_func_proto)
> +					return -EINVAL;
> +				nr_args = btf_type_vlen(prog->aux->attach_func_proto);
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Same question here for bpf_get_func_arg_cnt() - should this subtract 1 to
exclude the __data parameter from the count returned to BPF programs?

> +				/* Save nr_args to reg0 */
> +				insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, nr_args);

[ ... ]


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/21055137351