linux-hardening - Re: [PATCH] kasan: test: Bypass __alloc

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Date:   Wed, 6 Oct 2021 09:33:18 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] kasan: test: Bypass __alloc_size checks

On Wed, Oct 06, 2021 at 12:38:36PM +0100, Mark Rutland wrote:
> Hi Kees,
> 
> On Tue, Oct 05, 2021 at 08:55:22PM -0700, Kees Cook wrote:
> > Intentional overflows, as performed by the KASAN tests, are detected
> > at compile time[1] (instead of only at run-time) with the addition of
> > __alloc_size. Fix this by forcing the compiler into not being able to
> > trust the size used following the kmalloc()s.
> 
> It might be better to use OPTIMIZER_HIDE_VAR(), since that's intended to
> make the value opaque to the compiler, and volatile might not always do
> that depending on how the compiler tracks the variable.

Given both you and Jann[1] have suggested this, I'll send a v2 with that.
:) Thanks!

-Kees

[1] https://lore.kernel.org/lkml/CAG48ez19raco+s+UF8eiXqTvaDEoMAo6_qmW2KdO24QDpmZpFQ@mail.gmail.com/

-- 
Kees Cook