linux-kernel - Re: [PATCH v4 05/11] arm64: csum: Disable KASAN for do

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Date:   Wed, 22 Apr 2020 11:41:38 +0100
From:   Will Deacon <will@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        kernel-team@...roid.com, Michael Ellerman <mpe@...erman.id.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v4 05/11] arm64: csum: Disable KASAN for do_csum()

On Wed, Apr 22, 2020 at 10:49:52AM +0100, Mark Rutland wrote:
> On Tue, Apr 21, 2020 at 04:15:31PM +0100, Will Deacon wrote:
> > do_csum() over-reads the source buffer and therefore abuses
> > READ_ONCE_NOCHECK() to avoid tripping up KASAN. In preparation for
> > READ_ONCE_NOCHECK() becoming a macro, and therefore losing its
> > '__no_sanitize_address' annotation, just annotate do_csum() explicitly
> > and fall back to normal loads.
> > 
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: Robin Murphy <robin.murphy@....com>
> > Signed-off-by: Will Deacon <will@...nel.org>
> 
> From a functional perspective:
> 
> Acked-by: Mark Rutland <mark.rutland@....com>

Thanks.

> I know that Robin had a concern w.r.t. how this would affect the
> codegen, but I think we can follow that up after the series as a whole
> is merged.

Makes sense. I did look at the codegen, fwiw, and it didn't seem especially
bad. One of the LDP's gets cracked in the unlikely() path, but it didn't
look like it would be a disaster (and sprinkling barrier() around to force
the LDP felt really fragile!).

Will