From: Sasha Levin <sasha.levin@oracle.com>
To: Daniel Borkmann <dborkman@redhat.com>,
Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
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: Mon, 20 Oct 2014 10:13:21 -0400 [thread overview]
Message-ID: <54451881.3090302@oracle.com> (raw)
In-Reply-To: <5445179A.4080804@redhat.com>
On 10/20/2014 10:09 AM, Daniel Borkmann wrote:
> On 10/20/2014 03:58 PM, Andrey Ryabinin wrote:
>> On 10/20/2014 04:49 PM, Theodore Ts'o wrote:
>>> On Mon, Oct 20, 2014 at 03:03:22PM +0400, Andrey Ryabinin wrote:
>>>> Hi, Theodore.
>>>>
>>>> I've got this while booting kernel with ubsan:
>>>>
>>>> [ 0.000000] ================================================================================
>>>> [ 0.000000] UBSan: Undefined behaviour in ../include/linux/bitops.h:107:33
>>>> [ 0.000000] shift exponent 32 is to large for 32-bit type 'unsigned int'
>>> ...
>>>> [ 0.000000] _mix_pool_bytes (/home/andrew/linux/ubsan_x86//include/linux/bitopsh:107 /home/andrew/linux/ubsan_x86//drivers/char/randomc:509)
>>>
>>> So this doesn't make any sense to me. This is triggering here:
>>>
>>> w = rol32(*bytes++, input_rotate);
>>>
>>> .... but input_rotate should never be >= 32, since it is set this way:
>>>
>>
>> It's triggering when input_rotate == 0, so UBSan complains about right shift in rol32()
>>
>> static inline __u32 rol32(__u32 word, unsigned int shift)
>> {
>> return (word << shift) | (word >> (32 - shift));
>> }
>
> So that would be the case when the entropy store's input_rotate calls
> _mix_pool_bytes() for the very first time ... I don't think it's an
> issue though.
It's an issue because it's _undefined_. For all you know gcc could return
whatever it wants as the result (42?) - no one promises you a "0" there.
Thanks,
Sasha
next prev parent reply other threads:[~2014-10-20 14:14 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 [this message]
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
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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