linux-kernel - Re: [PATCH 3/3] asm-generic, x86: Add bitops instrumentation for KASAN

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Message-ID: <20190529120118.GQ2623@hirez.programming.kicks-ass.net>
Date:   Wed, 29 May 2019 14:01:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Dmitry Vyukov' <dvyukov@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH 3/3] asm-generic, x86: Add bitops instrumentation for
 KASAN

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.