linux-kernel - Re: [PATCH bpf-next v5 2/5] bpf: tcp: Mark bpf_load_hdr

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Message-ID: <4ed0fa29-dd37-4a7e-8ba6-c84af9d735d6@linux.dev>
Date: Mon, 16 Dec 2024 10:18:45 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Daniel Xu <dxu@...uu.xyz>
Cc: pabeni@...hat.com, kuba@...nel.org, andrii@...nel.org, ast@...nel.org,
 edumazet@...gle.com, memxor@...il.com, davem@...emloft.net,
 daniel@...earbox.net, eddyz87@...il.com, song@...nel.org,
 yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org,
 sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, horms@...nel.org,
 bpf@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 2/5] bpf: tcp: Mark bpf_load_hdr_opt() arg2 as
 read-write

On 12/12/24 3:22 PM, Daniel Xu wrote:
> MEM_WRITE attribute is defined as: "Non-presence of MEM_WRITE means that
> MEM is only being read". bpf_load_hdr_opt() both reads and writes from
> its arg2 - void *search_res.
> 
> This matters a lot for the next commit where we more precisely track
> stack accesses. Without this annotation, the verifier will make false
> assumptions about the contents of memory written to by helpers and
> possibly prune valid branches.

Acked-by: Martin KaFai Lau <martin.lau@...nel.org>