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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Tue, 31 Jul 2018 17:21:35 +0200
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Subject: Re: [PATCH v4 13/17] khwasan: add hooks implementation
To:     Andrey Ryabinin <aryabinin@virtuozzo.com>
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On Tue, Jul 31, 2018 at 4:50 PM, Andrey Ryabinin
<aryabinin@virtuozzo.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.