linux-kernel - Re: [PATCH bpf-next v9 02/23] bpf/verifier: do not clear meta in check_mem

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Date:   Tue, 30 Aug 2022 15:51:50 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     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>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>
Subject: Re: [PATCH bpf-next v9 02/23] bpf/verifier: do not clear meta in check_mem_size

On Fri, Aug 26, 2022 at 3:55 AM Kumar Kartikeya Dwivedi
<memxor@...il.com> wrote:
>
> On Wed, 24 Aug 2022 at 15:41, Benjamin Tissoires
> <benjamin.tissoires@...hat.com> wrote:
> >
> > The purpose of this clear is to prevent meta->raw_mode to be evaluated
> > at true, but this also prevents to forward any other data to the other
> > callees.
> >
> > Only switch back raw_mode to false so we don't entirely clear meta.
> >
> > Acked-by: Yonghong Song <yhs@...com>
> > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> >
> > ---
> >
> > no changes in v9
> >
> > no changes in v8
> >
> > no changes in v7
> >
> > new in v6
> > ---
> >  kernel/bpf/verifier.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index d694f43ab911..13190487fb12 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -5287,7 +5287,7 @@ static int check_mem_size_reg(struct bpf_verifier_env *env,
> >                  * initialize all the memory that the helper could
> >                  * just partially fill up.
> >                  */
> > -               meta = NULL;
> > +               meta->raw_mode = false;
>
> But this is adding a side effect, the caller's meta->raw_mode becomes
> false, which the caller may not expect...

Turns out that I don't need that patch anymore because I am not
checking against is_kfunc in the previous patch. So dropping it from
the next revision.

Cheers,
Benjamin

>
> >
> >         if (reg->smin_value < 0) {
> >                 verbose(env, "R%d min value is negative, either use unsigned or 'var &= const'\n",
> > --
> > 2.36.1
> >
>