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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
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