From mboxrd@z Thu Jan  1 00:00:00 1970
From: Will Deacon <will@kernel.org>
Subject: Re: [PATCH v4 05/11] arm64: csum: Disable KASAN for do_csum()
Date: Wed, 22 Apr 2020 11:41:38 +0100
Message-ID: <20200422104138.GA30265@willie-the-truck>
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To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, kernel-team@android.com, Michael Ellerman <mpe@ellerman.id.au>, Peter Zijlstra <peterz@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Segher Boessenkool <segher@kernel.crashing.org>, Christian Borntraeger <borntraeger@de.ibm.com>, Luc Van Oostenryck <luc.vanoostenryck@gmail.com>, Arnd Bergmann <arnd@arndb.de>, Peter Oberparleiter <oberpar@linux.ibm.com>, Masahiro Yamada <masahiroy@kernel.org>, Nick Desaulniers <ndesaulniers@google.com>, Robin Murphy <robin.murphy@arm.com>

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@arm.com>
> > Cc: Robin Murphy <robin.murphy@arm.com>
> > Signed-off-by: Will Deacon <will@kernel.org>
> 
> From a functional perspective:
> 
> Acked-by: Mark Rutland <mark.rutland@arm.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