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From: Dmitry Vyukov <dvyukov@google.com>
Date: Tue, 19 Dec 2017 10:07:58 +0100
Message-ID: <CACT4Y+aDiYaFT4MOE8q2unUi0Scp7Gfvo+DFMNNUpmYhoG_+uQ@mail.gmail.com>
Subject: Re: BUG: bad usercopy in memdup_user
To: "Tobin C. Harding" <me@tobin.cc>
Cc: Kees Cook <keescook@chromium.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Linux-MM <linux-mm@kvack.org>,
        syzbot 
        <bot+719398b443fd30155f92f2a888e749026c62b427@syzkaller.appspotmail.com>,
        David Windsor <dave@nullcore.net>, keun-o.park@darkmatter.ae,
        Laura Abbott <labbott@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        Mark Rutland <mark.rutland@arm.com>, Ingo Molnar <mingo@kernel.org>,
        syzkaller-bugs@googlegroups.com, Will Deacon <will.deacon@arm.com>
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On Tue, Dec 19, 2017 at 10:04 AM, Tobin C. Harding <me@tobin.cc> wrote:
>> >> > <penguin-kernel@i-love.sakura.ne.jp> wrote:
>> >> >> On 2017/12/18 22:40, syzbot wrote:
>> >> >>> Hello,
>> >> >>>
>> >> >>> syzkaller hit the following crash on 6084b576dca2e898f5c101baef151f7bfdbb606d
>> >> >>> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
>> >> >>> compiler: gcc (GCC) 7.1.1 20170620
>> >> >>> .config is attached
>> >> >>> Raw console output is attached.
>> >> >>>
>> >> >>> Unfortunately, I don't have any reproducer for this bug yet.
>> >> >>>
>> >> >>>
>> >> >>
>> >> >> This BUG is reporting
>> >> >>
>> >> >> [   26.089789] usercopy: kernel memory overwrite attempt detected to 0000000022a5b430 (kmalloc-1024) (1024 bytes)
>> >> >>
>> >> >> line. But isn't 0000000022a5b430 strange for kmalloc(1024, GFP_KERNEL)ed kernel address?
>> >> >
>> >> > The address is hashed (see the %p threads for 4.15).
>> >>
>> >>
>> >> +Tobin, is there a way to disable hashing entirely? The only
>> >> designation of syzbot is providing crash reports to kernel developers
>> >> with as much info as possible. It's fine for it to leak whatever.
>> >
>> > We have new specifier %px to print addresses in hex if leaking info is
>> > not a worry.
>>
>> This is not a per-printf-site thing. It's per-machine thing.
>
> There is no way to disable the hashing currently built into the system.

Ack.
Any kind of continuous testing systems would be a use case for this.