linux-kernel - Re: [PATCH v4 13/17] khwasan: add hooks implementation

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Message-ID: <01000164f0fd5abc-df9ea911-9701-498c-adce-9f833e6df3ed-000000@email.amazonses.com>
Date:   Tue, 31 Jul 2018 15:38:13 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        vincenzo.frascino@....com, Alexander Potapenko <glider@...gle.com>,
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        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
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        Dave Martin <dave.martin@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
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        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
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        Evgeniy Stepanov <eugenis@...gle.com>
Subject: Re: [PATCH v4 13/17] khwasan: add hooks implementation

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?