linux-kernel - Re: [PATCH v2 1/2] bpf: Specify access type of bpf_sysctl_get

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Message-ID: <f8ecfb2d-c82f-4785-b5dd-eccec0d13f8a@linux.dev>
Date: Tue, 10 Jun 2025 09:41:52 -0700
From: Yonghong Song <yonghong.song@...ux.dev>
To: Jerome Marchand <jmarchan@...hat.com>, bpf@...r.kernel.org
Cc: Martin KaFai Lau <martin.lau@...ux.dev>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, linux-kernel@...r.kernel.org,
 Eduard Zingerman <eddyz87@...il.com>
Subject: Re: [PATCH v2 1/2] bpf: Specify access type of bpf_sysctl_get_name
 args



On 6/10/25 2:19 AM, Jerome Marchand wrote:
> The second argument of bpf_sysctl_get_name() helper is a pointer to a
> buffer that is being written to. However that isn't specify in the
> prototype.
>
> Until commit 37cce22dbd51a ("bpf: verifier: Refactor helper access
> type tracking"), all helper accesses were considered as a possible
> write access by the verifier, so no big harm was done. However, since
> then, the verifier might make wrong asssumption about the content of
> that address which might lead it to make faulty optimizations (such as
> removing code that was wrongly labeled dead). This is what happens in
> test_sysctl selftest to the tests related to sysctl_get_name.
>
> Add MEM_WRITE flag the second argument of bpf_sysctl_get_name().
>
> Signed-off-by: Jerome Marchand <jmarchan@...hat.com>

Acked-by: Yonghong Song <yonghong.song@...ux.dev>