linux-kernel - Re: WARNING: kernel stack regs has bad 'bp' value (3)

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Date:   Sat, 12 May 2018 12:11:17 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Eric Biggers <ebiggers3@...il.com>,
        syzbot <syzbot+ffa3a158337bbc01ff09@...kaller.appspotmail.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Miller <davem@...emloft.net>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: WARNING: kernel stack regs has bad 'bp' value (3)

On 12 May 2018 at 11:50, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Sat, May 12, 2018 at 11:09 AM, Ard Biesheuvel
> <ard.biesheuvel@...aro.org> wrote:
>> (+ Arnd)
>>
>> On 12 May 2018 at 10:43, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>>> On Fri, Feb 2, 2018 at 11:18 PM, Eric Biggers <ebiggers3@...il.com> wrote:
>>>> On Fri, Feb 02, 2018 at 02:57:32PM +0100, Dmitry Vyukov wrote:
>>>>> On Fri, Feb 2, 2018 at 2:48 PM, syzbot
>>>>> <syzbot+ffa3a158337bbc01ff09@...kaller.appspotmail.com> wrote:
>>>>> > Hello,
>>>>> >
>>>>> > syzbot hit the following crash on upstream commit
>>>>> > 7109a04eae81c41ed529da9f3c48c3655ccea741 (Thu Feb 1 17:37:30 2018 +0000)
>>>>> > Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/ide
>>>>> >
>>>>> > So far this crash happened 4 times on net-next, upstream.
>>>>> > C reproducer is attached.
>>>>> > syzkaller reproducer is attached.
>>>>> > Raw console output is attached.
>>>>> > compiler: gcc (GCC) 7.1.1 20170620
>>>>> > .config is attached.
>>>>>
>>>>>
>>>>> From suspicious frames I see salsa20_asm_crypt there, so +crypto maintainers.
>>>>>
>>>>
>>>> Looks like the x86 implementations of Salsa20 (both i586 and x86_64) need to be
>>>> updated to not use %ebp/%rbp.
>>>
>>> Ard,
>>>
>>> This was bisected as introduced by:
>>>
>>> commit 83dee2ce1ae791c3dc0c9d4d3a8d42cb109613f6
>>> Author: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>>> Date:   Fri Jan 19 12:04:34 2018 +0000
>>>
>>>     crypto: sha3-generic - rewrite KECCAK transform to help the
>>> compiler optimize
>>>
>>> https://gist.githubusercontent.com/dvyukov/47f93f5a0679170dddf93bc019b42f6d/raw/65beac8ddd30003bbd4e9729236dc8572094abf7/gistfile1.txt
>>
>> Ouch.
>>
>> I'm not an expert in x86 assembly. Could someone please check the
>> generated code to see what's going on? The C code changes are not that
>> intricate, they basically unroll a loop, replacing accesses to
>> 'array[indirect_index[i]]' with 'array[constant]'.
>>
>> As mentioned in the commit log, the speedup is more than significant
>> for architectures with lots of GPRs so I'd prefer fixing the patch
>> over reverting it (if there is anything wrong with the code in the
>> first place)
>
> I suspect the problem is with __attribute__((__optimize__("O3"))). It
> makes compiler use rbp register, which must not be used.

IIRC, the additional speedup from adding that was significant but not
huge. Given that we don't use O3 anywhere else, I guess we should just
remove it.

Could you please check whether that makes the issue go away?

If so,

Acked-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

for any patch that removes the O3 attribute override from keccakf()

Thanks,
Ard.