linux-kernel - Re: [RFC PATCH bpf-next 2/2] bpf: Get fentry func addr from user when BTF info invalid

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Message-ID: <cbb2a2d2-0810-4ea7-946f-bb592ba31d18@linux.dev>
Date: Tue, 6 May 2025 11:17:28 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>,
 Alan Maguire <alan.maguire@...cle.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 John Fastabend <john.fastabend@...il.com>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
 KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
 Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
 bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH bpf-next 2/2] bpf: Get fentry func addr from user when
 BTF info invalid

在 2025/5/1 06:23, Alexei Starovoitov 写道:
> On Wed, Apr 30, 2025 at 10:57 AM Alan Maguire <alan.maguire@...cle.com> wrote:
>>> +
>>> +                     if (!addr && (prog->expected_attach_type == BPF_TRACE_FENTRY ||
>>> +                                     prog->expected_attach_type == BPF_TRACE_FEXIT)) {
>>> +                             fname = kallsyms_lookup((unsigned long)prog->aux->fentry_func,
>>> +                                                     NULL, NULL, NULL, trace_symbol);
>>> +                             if (fname)
>>> +                                     addr = (long)prog->aux->fentry_func;
>>
>>
>> We should do some validation that the fname we get back matches the BTF
>> func name prefix (fname "foo.isra.0" matches "foo") I think?
> 
> I don't think that will be enough.
> User space should not be able to pass a random kernel address
> and convince the kernel that it matches a particular btf_id.
> As discussed in the other thread matching based on name is
> breaking apart.
> pahole does all the safety check to make sure name/addr/btf_id
> are consistent.
> We shouldn't be adding workarounds like this because
> pahole/btf/kernel build is not smart enough.
> 

Got it thanks for your reply, it is hoped that pahole/btf can have a 
better way to solve such problems.

> pw-bot: cr


-- 
Best Regards
Tao Chen