linux-kernel - Re: [PATCH v8 1/5] kasan: support backing vmalloc space with real shadow memory

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Message-ID: <875zkqtt7g.fsf@dja-thinkpad.axtens.net>
Date:   Tue, 15 Oct 2019 17:32:03 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org, x86@...nel.org,
        glider@...gle.com, luto@...nel.org, linux-kernel@...r.kernel.org,
        dvyukov@...gle.com, christophe.leroy@....fr,
        linuxppc-dev@...ts.ozlabs.org, gor@...ux.ibm.com
Subject: Re: [PATCH v8 1/5] kasan: support backing vmalloc space with real shadow memory


> There is a potential problem here, as Will Deacon wrote up at:
>
>   https://lore.kernel.org/linux-arm-kernel/20190827131818.14724-1-will@kernel.org/
>
> ... in the section starting:
>
> | *** Other architecture maintainers -- start here! ***
>
> ... whereby the CPU can spuriously fault on an access after observing a
> valid PTE.
>
> For arm64 we handle the spurious fault, and it looks like x86 would need
> something like its vmalloc_fault() applying to the shadow region to
> cater for this.

I'm not really up on x86 - my first thought would be that their stronger
memory ordering might be sufficient but I really don't know. Reading the
thread I see arm and powerpc discussions but nothing from anyone else,
so I'm none the wiser there...

Andy, do you have any thoughts?

Regards,
Daniel

>
> Thanks,
> Mark.