linux-kernel - Re: [PATCH bpf-next v9 01/23] bpf/verifier: allow all functions to read user provided context

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Date:   Fri, 2 Sep 2022 15:11:38 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Jiri Kosina <jikos@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Dave Marchevsky <davemarchevsky@...com>,
        Joe Stringer <joe@...ium.io>, Jonathan Corbet <corbet@....net>,
        Tero Kristo <tero.kristo@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH bpf-next v9 01/23] bpf/verifier: allow all functions to
 read user provided context

On Fri, Sep 2, 2022 at 5:50 AM Kumar Kartikeya Dwivedi <memxor@...il.com> wrote:
>
> On Thu, 1 Sept 2022 at 18:48, Benjamin Tissoires
> <benjamin.tissoires@...hat.com> wrote:
> >
> > [...]
> > If the above is correct, then yes, it would make sense to me to have 2
> > distinct functions: one to check for the args types only (does the
> > function definition in the problem matches BTF), and one to check for
> > its use.
> > Behind the scenes, btf_check_subprog_arg_match() calls
> > btf_check_func_arg_match() which is the one function with entangled
> > arguments type checking and actually assessing that the values
> > provided are correct.
> >
> > I can try to split that  btf_check_func_arg_match() into 2 distinct
> > functions, though I am not sure I'll get it right.
>
> FYI, I've already split them into separate functions in my tree
> because it had become super ugly at this point with all the new
> support and I refactored it to add the linked list helpers support
> using kfuncs (which requires some special handling for the args), so I
> think you can just leave it with a "processing_call" check in for your
> series for now.
>

great, thanks a lot.
Actually, writing the patch today with the "processing_call" was
really easy now that I have turned the problem in my head a lot
yesterday.

I am about to send v10 with the reviews addressed.

Cheers,
Benjamin