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Date: Tue, 31 Jul 2018 15:38:13 +0000
From: Christopher Lameter <cl@linux.com>
Subject: Re: [PATCH v4 13/17] khwasan: add hooks implementation
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To: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>, Andrey Konovalov <andreyknvl@google.com>, vincenzo.frascino@arm.com, Alexander Potapenko <glider@google.com>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Andrew Morton <akpm@linux-foundation.org>, Mark Rutland <mark.rutland@arm.com>, Nick Desaulniers <ndesaulniers@google.com>, Marc Zyngier <marc.zyngier@arm.com>, Dave Martin <dave.martin@arm.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, "Eric W . Biederman" <ebiederm@xmission.com>, Ingo Molnar <mingo@kernel.org>, Paul Lawrence <paullawrence@google.com>, Geert Uytterhoeven <geert@linux-m68k.org>, Arnd Bergmann <arnd@arndb.de>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Kate Stewart <kstewart@linuxfoundation.org>, Mike Rapoport <rppt@linux.vnet.ibm.com>, kasan-dev <kasan-dev@googlegroups.com>, linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, linux-sparse@vger.kernel.org, Linux Memory Management List <linux-mm@kvack.org>, Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>, Chintan Pandya <cpandya@codeaurora.org>, Jacob Bramley <Jacob.Bramley@arm.com>, Jann Horn <jannh@google.com>, Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>, Lee Smith <Lee.Smith@arm.com>, Kostya Serebryany <kcc@google.com>, Mark Brand <markbrand@google.com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>, Evgeniy Stepanov <eugenis@google.com>

On Tue, 31 Jul 2018, Dmitry Vyukov wrote:

> > Actually you should do this for SLAB_TYPESAFE_BY_RCU slabs. Usually they are with ->ctors but there
> > are few without constructors.
> > We can't reinitialize or even retag them. The latter will definitely cause false-positive use-after-free reports.
>
> Somewhat offtopic, but I can't understand how SLAB_TYPESAFE_BY_RCU
> slabs can be useful without ctors or at least memset(0). Objects in
> such slabs need to be type-stable, but I can't understand how it's
> possible to establish type stability without a ctor... Are these bugs?
> Or I am missing something subtle? What would be a canonical usage of
> SLAB_TYPESAFE_BY_RCU slab without a ctor?

True that sounds fishy. Would someone post a list of SLAB_TYPESAFE_BY_RCU
slabs without ctors?