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

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Message-ID: <5069848.31r3eYUQgx@7940hx>
Date: Fri, 16 Jan 2026 14:56:01 +0800
From: Menglong Dong <menglong.dong@...ux.dev>
To: menglong8.dong@...il.com, ast@...nel.org, bot+bpf-ci@...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

On 2026/1/16 12:20 bot+bpf-ci@...nel.org write:
> > 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?

You are right about this point too. The wrong selftests made me
ignore this point :/

Thanks!
Menglong Dong

> 
> > +				/* 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
>