netdev - Re: [PATCH RESEND bpf-next v3 2/9] bpf: verifier: refactor check_attach_btf

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Date:   Fri, 11 Sep 2020 21:50:55 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>,
        KP Singh <kpsingh@...omium.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH RESEND bpf-next v3 2/9] bpf: verifier: refactor
 check_attach_btf_id()

Andrii Nakryiko <andrii.nakryiko@...il.com> writes:

> On Fri, Sep 11, 2020 at 3:00 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>>
>> From: Toke Høiland-Jørgensen <toke@...hat.com>
>>
>> The check_attach_btf_id() function really does three things:
>>
>> 1. It performs a bunch of checks on the program to ensure that the
>>    attachment is valid.
>>
>> 2. It stores a bunch of state about the attachment being requested in
>>    the verifier environment and struct bpf_prog objects.
>>
>> 3. It allocates a trampoline for the attachment.
>>
>> This patch splits out (1.) and (3.) into separate functions in preparation
>> for reusing them when the actual attachment is happening (in the
>> raw_tracepoint_open syscall operation), which will allow tracing programs
>> to have multiple (compatible) attachments.
>>
>> No functional change is intended with this patch.
>>
>> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
>> ---
>
> I can't tell if there are any functional changes or not, tbh. The
> logic is quite complicated and full of intricate details. I did leave
> some suggestions on hopefully simplifying code flow in some places
> (and ensuring it's harder to break it on future changes), but I hope
> Alexei will give it a very thorough review and check that none of the
> subtle details broke.

Yeah, totally agree this is gnarly... :/
Which is also why I chickened out of doing any further changes in an
attempt to simplify the flow, but rather kept as much as the existing
structure as possible (with somewhat mixed results, I suppose).

Let's see what Alexei thinks. I guess I can take another crack at it, in
which case, thank you for the suggestions for simplifying things!

-Toke