From: Dmitry Vyukov <dvyukov@google.com>
Subject: Re: WARNING: kernel stack regs has bad 'bp' value (3)
Date: Sat, 12 May 2018 11:50:36 +0200
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Cc: Arnd Bergmann <arnd@arndb.de>, Eric Biggers <ebiggers3@gmail.com>,
        syzbot <syzbot+ffa3a158337bbc01ff09@syzkaller.appspotmail.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        David Miller <davem@davemloft.net>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE"
        <linux-crypto@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
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On Sat, May 12, 2018 at 11:09 AM, Ard Biesheuvel
<ard.biesheuvel@linaro.org> wrote:
> (+ Arnd)
>
> On 12 May 2018 at 10:43, Dmitry Vyukov <dvyukov@google.com> wrote:
>> On Fri, Feb 2, 2018 at 11:18 PM, Eric Biggers <ebiggers3@gmail.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@syzkaller.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@linaro.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.