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From: Sasha Levin <sasha.levin@oracle.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>,
	Daniel Borkmann <dborkman@redhat.com>,
	Andrey Ryabinin <a.ryabinin@samsung.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Michal Marek <mmarek@suse.cz>,
	x86@kernel.org, linux-kbuild@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Dmitry Vyukov <dvyukov@google.com>,
	Konstantin Khlebnikov <koct9i@gmail.com>
Subject: Re: drivers: random: Shift out-of-bounds in _mix_pool_bytes
Date: Fri, 24 Oct 2014 11:04:11 -0400	[thread overview]
Message-ID: <544A6A6B.3040602@oracle.com> (raw)
In-Reply-To: <20141024134205.GB21513@worktop.programming.kicks-ass.net>

On 10/24/2014 09:42 AM, Peter Zijlstra wrote:
> On Fri, Oct 24, 2014 at 09:23:35AM -0400, Sasha Levin wrote:
>>
>> i >> 32 may happen to be "i", but is there anything that prevents the compiler
>> from returning, let's say, 42?
> 
> Not really, although gcc seems to opt for the 'sane' option and emit the
> instruction and let the arch figure out how to deal with it. Hence the
> 'fun' difference between x86 and ARM.

It's interesting how many different views on undefined behaviour there are between
kernel folks.

Everything between Ted Ts'o saying that GCC can launch nethack on oversized shifts,
to DaveM saying he will file a GCC bug if the behaviour isn't sane w.r.t to memcpy().


Thanks,
Sasha

  reply	other threads:[~2014-10-24 15:05 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-20 10:54 [RFC] UBSan: run-time undefined behavior sanity checker Andrey Ryabinin
2014-10-20 10:54 ` [RFC PATCH] " Andrey Ryabinin
2014-10-20 19:35   ` Sasha Levin
2014-10-21  8:03     ` Andrey Ryabinin
2014-10-24  8:31       ` y.gribov
2014-10-24 10:36         ` Andrey Ryabinin
2014-10-21  9:47   ` Peter Zijlstra
2014-10-21 10:09     ` Andrey Ryabinin
2014-10-24 10:30       ` Peter Zijlstra
2014-10-21 17:06   ` Randy Dunlap
2014-10-22  9:58   ` Rasmus Villemoes
2014-10-22 11:16     ` Andrey Ryabinin
2014-10-20 11:03 ` drivers: random: Shift out-of-bounds in _mix_pool_bytes Andrey Ryabinin
2014-10-20 12:49   ` Theodore Ts'o
2014-10-20 13:58     ` Andrey Ryabinin
2014-10-20 14:08       ` Theodore Ts'o
2014-10-20 14:09       ` Daniel Borkmann
2014-10-20 14:13         ` Sasha Levin
2014-10-20 14:16         ` Theodore Ts'o
2014-10-20 14:42           ` Andrey Ryabinin
2014-10-24 10:01           ` Peter Zijlstra
2014-10-24 10:16             ` Andrey Ryabinin
2014-10-24 13:23             ` Sasha Levin
2014-10-24 13:42               ` Peter Zijlstra
2014-10-24 15:04                 ` Sasha Levin [this message]
2014-10-24 15:10                   ` Dmitry Vyukov
2014-10-24 21:05                     ` One Thousand Gnomes
2014-10-24 22:23                       ` H. Peter Anvin
2014-10-24 22:09                     ` Andreas Dilger
2014-10-24 22:22                       ` H. Peter Anvin
2014-10-25  0:50                         ` Sasha Levin
2014-10-25 20:30                           ` One Thousand Gnomes
2014-10-25 20:49                             ` Andrey Ryabinin
2014-10-20 11:07 ` kernel: clockevents: shift out-of-bounds Andrey Ryabinin
2014-10-24 10:25   ` Peter Zijlstra
2014-10-20 11:16 ` fs: ext4: mballoc: negative shift exponent Andrey Ryabinin
2014-10-20 11:23 ` jbd2: revoke: negative shift exponent in hash() Andrey Ryabinin

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