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Date:   Wed, 29 May 2019 14:01:18 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     David Laight <David.Laight@ACULAB.COM>
Cc:     'Dmitry Vyukov' <dvyukov@google.com>,
        Marco Elver <elver@google.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
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        LKML <linux-kernel@vger.kernel.org>,
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        kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: [PATCH 3/3] asm-generic, x86: Add bitops instrumentation for
 KASAN
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On Wed, May 29, 2019 at 11:20:56AM +0000, David Laight wrote:
> From: Dmitry Vyukov
> > Sent: 29 May 2019 11:57

> > Interesting. Does an address passed to bitops also should be aligned,
> > or alignment is supposed to be handled by bitops themselves?
> 
> The bitops are defined on 'long []' and it is expected to be aligned.
> Any code that casts the argument is likely to be broken on big-endian.
> I did a quick grep a few weeks ago and found some very dubious code.
> Not all the casts seemed to be on code that was LE only (although
> I didn't try to find out what the casts were from).
> 
> The alignment trap on x86 could be avoided by only ever requesting 32bit
> cycles - and assuming the buffer is always 32bit aligned (eg int []).
> But on BE passing an 'int []' is just so wrong ....

Right, but as argued elsewhere, I feel we should clean up the dubious
code instead of enabling it.