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Date: Tue, 25 Jul 2017 18:20:02 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Kees Cook <keescook@...omium.org>
Cc: Li Kun <hw.likun@...wei.com>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Will Deacon <will.deacon@....com>,
Mark Rutland <mark.rutland@....com>, Laura Abbott <labbott@...oraproject.org>
Subject: Re: [RFC PATCH untested] arm64: kernel: implement fast refcount checking
On 25 July 2017 at 18:13, Kees Cook <keescook@...omium.org> wrote:
> On Tue, Jul 25, 2017 at 4:49 AM, Ard Biesheuvel
> <ard.biesheuvel@...aro.org> wrote:
>> Hi all,
>>
>> I had a stab at porting the fast refcount checks to arm64. It is slightly
>> less straight-forward than x86 given that we need to support both LSE and
>> LL/SC, and fallback to the latter if running a kernel built with support
>> for the former on hardware that does not support it.
>>
>> It is build tested with and without LSE support, and boots fine on non-LSE
>> hardware in both cases.
>
> Ah! Very cool. Hopefully you and Li can compare notes; I think they've
> been working on an implementation too.
>
I wasn't aware of that.
>> Suggestions welcome as to how to test and/or benchmark this,
>
> I'll post a patch for LKDTM that I've been using. It's more
> comprehensive than the existing ATOMIC checks (which predated the
> refcount-only protection).
>
OK. One thing I couldn't figure out: is refcount_t signed or not? The
saturate tests set the initial value to UINT_MAX - 1, but this is
interpreted as a negative value and so the refcount manipulations that
are expected to succeed also fail in my case.
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