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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Mon, 11 Jun 2018 10:13:42 +0200
Message-ID: <CAKv+Gu-RXe3baYUWw1dvBJdD7MBuB6Zg6rN5rVYyotcQgTvmdg@mail.gmail.com>
Subject: Re: WARNING: kernel stack regs has bad 'bp' value (3)
To:     Dmitry Vyukov <dvyukov@google.com>
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>
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On 8 June 2018 at 11:54, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Sat, May 26, 2018 at 9:22 AM, Eric Biggers <ebiggers3@gmail.com> wrote:
>> On Sat, May 12, 2018 at 10:43:08AM +0200, Dmitry Vyukov 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
>>
>> Note that syzbot's original C reproducer (from Feb 1) for this actually
>> triggered the warning through salsa20-asm, which I've just proposed to "fix" by
>> https://patchwork.kernel.org/patch/10428863/.  sha3-generic is apparently
>> another instance of the same bug, where the %rbp register is used for data.
>
>
> Mailed "crypto: don't optimize keccakf()" to fix this.
>
> Amusingly __optimize("O3") always lead to degraded performance as gcc does not
> inline across different optimizations levels, so keccakf() wasn't inlined
> into its callers and keccakf_round() wasn't inlined into keccakf().

That does not make sense. The -O3 definitely made the code run
slightly faster on AArch64, but I don't remember the exact numbers or
the compiler version.

In any case, it wasn't an improvement worth obsessing about compared
to the 14x speedup I got on A53 from rewriting the code itself.