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

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Date:   Tue, 31 Jul 2018 17:21:35 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     vincenzo.frascino@....com, Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Dave Martin <dave.martin@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Ingo Molnar <mingo@...nel.org>,
        Paul Lawrence <paullawrence@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
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        Lee Smith <Lee.Smith@....com>,
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        Mark Brand <markbrand@...gle.com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Evgeniy Stepanov <eugenis@...gle.com>
Subject: Re: [PATCH v4 13/17] khwasan: add hooks implementation

On Tue, Jul 31, 2018 at 4:50 PM, Andrey Ryabinin
<aryabinin@...tuozzo.com> wrote:
> On 07/31/2018 04:05 PM, Andrey Konovalov wrote:
>> We can assign tags to objects with constructors when a slab is
>> allocated and call constructors once as usual. The downside is that
>> such object would always have the same tag when it is reallocated, so
>> we won't catch use-after-frees.
>
> 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.
>
> As for non-SLAB_TYPESAFE_BY_RCU caches with constructors, it's probably ok to reinitialize and retag such objects.
> I don't see how could any code rely on the current ->ctor() behavior in non-SLAB_TYPESAFE_BY_RCU case,
> unless it does something extremely stupid or weird.
> But let's not do it now. If you care, you cand do it later, with a separate patch, so we could just revert
> it if anything goes wrong.

OK, will do it then when there's either a constructor or the slab is
SLAB_TYPESAFE_BY_RCU.