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Date:   Wed, 6 Oct 2021 09:33:18 -0700
From:   Kees Cook <>
To:     Mark Rutland <>
Cc:     Andrew Morton <>,
        Andrey Ryabinin <>,
        Alexander Potapenko <>,
        Andrey Konovalov <>,
        Dmitry Vyukov <>,,,
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 Cook

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