linux-kernel - Re: [kernel-hardening] Re: [PATCH v2 1/4] siphash: add cryptographically secure hashtable function

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Message-ID: <CAHmME9p+xEBTKz+Wfy5Ypav4HU7H+rnA-0hLgd1sMmthDzOmvw@mail.gmail.com>
Date:   Thu, 15 Dec 2016 22:11:24 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     kernel-hardening@...ts.openwall.com
Cc:     Hannes Frederic Sowa <hannes@...essinduktion.org>,
        David Laight <David.Laight@...lab.com>,
        Netdev <netdev@...r.kernel.org>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        "Daniel J . Bernstein" <djb@...yp.to>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Eric Biggers <ebiggers3@...il.com>
Subject: Re: [kernel-hardening] Re: [PATCH v2 1/4] siphash: add
 cryptographically secure hashtable function

On Thu, Dec 15, 2016 at 10:09 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, Dec 15, 2016 at 07:50:36PM +0100, Jason A. Donenfeld wrote:
>> There's no 32-bit platform
>> that will trap on a 64-bit unaligned access because there's no such
>> thing as a 64-bit access there. In short, we're fine.
>
> ARMv7 LPAE is a 32bit architecture that has 64bit load/stores IIRC.
>
> x86 has cmpxchg8b that can do 64bit things and very much wants the u64
> aligned.
>
> Also, IIRC we have a few platforms where u64 doesn't carry 8 byte
> alignment, m68k or something like that, but yes, you likely don't care.

Indeed, I stand corrected. But in any case, the use of __aligned(8) in
the patchset ensures that things are fixed and that we don't have this
issue.