From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: Re: WARNING: kernel stack regs has bad 'bp' value (3)
Date: Sat, 12 May 2018 11:09:48 +0200
Message-ID: <CAKv+Gu_Lh1TroS4BJJp4PQNYbqZ8KR=6Z5hHX2+UiBfxC=sxQA@mail.gmail.com>
References: <001a11449aa2faf11805643af581@google.com> <CACT4Y+YOmbZGdBbFpmjRJXABGe1tD=F+3na77DwoPCEaROADyw@mail.gmail.com>
 <20180202221829.tdiji2332t7orcxj@gmail.com> <CACT4Y+afpDQ7A3caRmskML06h8Q6+NkVAn6HtV93ExPec-g2pA@mail.gmail.com>
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Cc: 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: Dmitry Vyukov <dvyukov@google.com>, Arnd Bergmann <arnd@arndb.de>
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(+ 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)

-- 
Ard.