linux-kernel - Re: [PATCH bpf-next v3 1/2] bpf: support bpf_get_func_arg() for BPF_TRACE_RAW

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Message-Id: <c83188087c6d6409524b80b2078285813ccfea8e42ea82e88542e6e8d5e5f73d@mail.kernel.org>
Date: Mon, 19 Jan 2026 18:44:53 +0000 (UTC)
From: bot+bpf-ci@...nel.org
To: menglong8.dong@...il.com,andrii@...nel.org,ast@...nel.org
Cc: daniel@...earbox.net,john.fastabend@...il.com,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 v3 1/2] bpf: support bpf_get_func_arg() for BPF_TRACE_RAW_TP

> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index f73e08c223b5..64976009ba3c 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1734,11 +1734,11 @@ tracing_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  	case BPF_FUNC_d_path:
>  		return &bpf_d_path_proto;
>  	case BPF_FUNC_get_func_arg:
> -		return bpf_prog_has_trampoline(prog) ? &bpf_get_func_arg_proto : NULL;
> +		return &bpf_get_func_arg_proto;

Removing the bpf_prog_has_trampoline() check here allows all TRACING
program types to use bpf_get_func_arg(), not just RAW_TP and trampoline-
based types. In particular, BPF_TRACE_ITER programs can now use this
helper.

However, looking at do_misc_fixups() in verifier.c, the inline code
generation only handles BPF_TRACE_RAW_TP specially. For other non-
trampoline types like BPF_TRACE_ITER, the else branch generates:

    BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8)

This loads nr_args from ctx-8, but ITER programs use a different context
layout (e.g. struct bpf_iter__bpf_map_elem with meta, map, key, value
pointers). There is no nr_args at ctx-8 for ITER programs.

Would this cause ITER programs using bpf_get_func_arg() to read arbitrary
memory at ctx-8, potentially leaking kernel data or causing incorrect
bounds checks for subsequent argument access?

>  	case BPF_FUNC_get_func_ret:
>  		return bpf_prog_has_trampoline(prog) ? &bpf_get_func_ret_proto : NULL;
>  	case BPF_FUNC_get_func_arg_cnt:
> -		return bpf_prog_has_trampoline(prog) ? &bpf_get_func_arg_cnt_proto : NULL;
> +		return &bpf_get_func_arg_cnt_proto;

Same question applies here for bpf_get_func_arg_cnt() with ITER programs.

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 9de0ec0c3ed9..0b281b7c41eb 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -23323,8 +23323,20 @@ 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 = btf_type_vlen(prog->aux->attach_func_proto);
> +
> +				/*
> +				 * skip first 'void *__data' argument in btf_trace_##name
> +				 * typedef
> +				 */
> +				nr_args--;
> +				/* 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);
> +			}

This else branch now applies to BPF_TRACE_ITER as well, since the
trampoline check was removed in tracing_prog_func_proto(). Should the
condition be extended to also handle ITER, or should ITER be explicitly
blocked from using these helpers?

[ ... ]


---
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/21147849826