linux-kernel - Re: [PATCH v2 1/2] bpf: Add bpf_has_frame

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Message-ID: <y27knofa4opun2vn3xjrowbtgphzkjo24lbfvdxc2segiztihu@k6q7f6ymronr>
Date: Thu, 4 Dec 2025 09:02:13 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Jiri Olsa <olsajiri@...il.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, 
	live-patching@...r.kernel.org, bpf@...r.kernel.org, 
	Andrey Grodzovsky <andrey.grodzovsky@...wdstrike.com>, Petr Mladek <pmladek@...e.com>, Song Liu <song@...nel.org>, 
	Raja Khan <raja.khan@...wdstrike.com>, Miroslav Benes <mbenes@...e.cz>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 1/2] bpf: Add bpf_has_frame_pointer()

On Thu, Dec 04, 2025 at 03:04:23PM +0100, Jiri Olsa wrote:
> On Wed, Dec 03, 2025 at 07:32:15PM -0800, Josh Poimboeuf wrote:
> >  	EMIT1(0xC9); /* leave */
> > +	if (im)
> > +		im->ksym.fp_end = prog - (u8 *)rw_image;
> 
> is the null check needed? there are other places in the function that
> use 'im' without that

That was a NULL pointer dereference found by BPF CI.
bpf_struct_ops_prepare_trampoline() calls arch_prepare_bpf_trampoline()
with NULL im.

-- 
Josh