linux-kernel - Re: [PATCH bpf-next v3 1/2] bpf: Fix memory access flags in helper prototypes

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Message-ID: <00d9e1ea7e4eef7a7891200a03e99083cdbd066c.camel@gmail.com>
Date: Tue, 20 Jan 2026 09:56:03 -0800
From: Eduard Zingerman <eddyz87@...il.com>
To: Zesen Liu <ftyghome@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
 <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>,  Song Liu
 <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, John Fastabend	
 <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav
 Fomichev	 <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa
 <jolsa@...nel.org>,  Matt Bobrowski <mattbobrowski@...gle.com>, Steven
 Rostedt <rostedt@...dmis.org>, Masami Hiramatsu	 <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,  "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
 <horms@...nel.org>, Daniel Xu <dxu@...uu.xyz>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, netdev@...r.kernel.org, Shuran Liu
	 <electronlsr@...il.com>, Peili Gao <gplhust955@...il.com>, Haoran Ni
	 <haoran.ni.cs@...il.com>
Subject: Re: [PATCH bpf-next v3 1/2] bpf: Fix memory access flags in helper
 prototypes

On Tue, 2026-01-20 at 16:28 +0800, Zesen Liu wrote:
> After commit 37cce22dbd51 ("bpf: verifier: Refactor helper access type tracking"),
> the verifier started relying on the access type flags in helper
> function prototypes to perform memory access optimizations.
> 
> Currently, several helper functions utilizing ARG_PTR_TO_MEM lack the
> corresponding MEM_RDONLY or MEM_WRITE flags. This omission causes the
> verifier to incorrectly assume that the buffer contents are unchanged
> across the helper call. Consequently, the verifier may optimize away
> subsequent reads based on this wrong assumption, leading to correctness
> issues.
> 
> For bpf_get_stack_proto_raw_tp, the original MEM_RDONLY was incorrect
> since the helper writes to the buffer. Change it to ARG_PTR_TO_UNINIT_MEM
> which correctly indicates write access to potentially uninitialized memory.
> 
> Similar issues were recently addressed for specific helpers in commit
> ac44dcc788b9 ("bpf: Fix verifier assumptions of bpf_d_path's output buffer")
> and commit 2eb7648558a7 ("bpf: Specify access type of bpf_sysctl_get_name args").
> 
> Fix these prototypes by adding the correct memory access flags.
> 
> Fixes: 37cce22dbd51 ("bpf: verifier: Refactor helper access type tracking")
> Co-developed-by: Shuran Liu <electronlsr@...il.com>
> Signed-off-by: Shuran Liu <electronlsr@...il.com>
> Co-developed-by: Peili Gao <gplhust955@...il.com>
> Signed-off-by: Peili Gao <gplhust955@...il.com>
> Co-developed-by: Haoran Ni <haoran.ni.cs@...il.com>
> Signed-off-by: Haoran Ni <haoran.ni.cs@...il.com>
> Signed-off-by: Zesen Liu <ftyghome@...il.com>
> ---

Acked-by: Eduard Zingerman <eddyz87@...il.com>