linux-kernel - Re: [PATCH v2 0/3] ubsan: Split out bounds checker

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Date:   Fri, 22 Nov 2019 08:52:15 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Elena Petrova <lenaptr@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: [PATCH v2 0/3] ubsan: Split out bounds checker

On Fri, Nov 22, 2019 at 10:07:29AM +0100, Dmitry Vyukov wrote:
> On Thu, Nov 21, 2019 at 7:15 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > v2:
> >     - clarify Kconfig help text (aryabinin)
> >     - add reviewed-by
> >     - aim series at akpm, which seems to be where ubsan goes through?
> > v1: https://lore.kernel.org/lkml/20191120010636.27368-1-keescook@chromium.org
> >
> > This splits out the bounds checker so it can be individually used. This
> > is expected to be enabled in Android and hopefully for syzbot. Includes
> > LKDTM tests for behavioral corner-cases (beyond just the bounds checker).
> >
> > -Kees
> 
> +syzkaller mailing list
> 
> This is great!
> 
> I wanted to enable UBSAN on syzbot for a long time. And it's
> _probably_ not lots of work. But it was stuck on somebody actually
> dedicating some time specifically for it.
> Kees, or anybody else interested, could you provide relevant configs
> that (1) useful for kernel, (2) we want 100% cleanliness, (3) don't
> fire all the time even without fuzzing? Anything else required to
> enable UBSAN? I don't see anything. syzbot uses gcc 8.something, which
> I assume should be enough (but we can upgrade if necessary).

Nothing external should be needed; GCC and Clang support the ubsan
options. Once this series lands, it should be possible to just enable
this with:

CONFIG_UBSAN=y
CONFIG_UBSAN_BOUNDS=y
# CONFIG_UBSAN_MISC is not set

Based on initial testing, the bounds checker isn't very noisy, but I
haven't spun up a syzbot instance to really confirm this yet (that was
on the TODO list for today to let it run over the weekend).

-- 
Kees Cook