linux-kernel - Re: KMSAN: uninit-value in mpol_rebind

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Message-ID: <52835ef5-6351-3852-d4ba-b6de285f96f5@suse.cz>
Date:   Fri, 4 Jan 2019 09:50:31 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+b19c2dc2c990ea657a71@...kaller.appspotmail.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, linux@...inikbrodowski.net,
        Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        xieyisheng1@...wei.com, zhong jiang <zhongjiang@...wei.com>
Subject: Re: KMSAN: uninit-value in mpol_rebind_mm

On 1/3/19 9:42 AM, Dmitry Vyukov wrote:
> On Thu, Jan 3, 2019 at 9:36 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>>
>>
>> On 12/31/18 8:51 AM, syzbot wrote:
>>> Hello,
>>>
>>> syzbot found the following crash on:
>>>
>>> HEAD commit:    79fc24ff6184 kmsan: highmem: use kmsan_clear_page() in cop..
>>> git tree:       kmsan
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=13c48b67400000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=901dd030b2cc57e7
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=b19c2dc2c990ea657a71
>>> compiler:       clang version 8.0.0 (trunk 349734)
>>>
>>> Unfortunately, I don't have any reproducer for this crash yet.
>>>
>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>> Reported-by: syzbot+b19c2dc2c990ea657a71@...kaller.appspotmail.com
>>>
>>> ==================================================================
>>> BUG: KMSAN: uninit-value in mpol_rebind_policy mm/mempolicy.c:353 [inline]
>>> BUG: KMSAN: uninit-value in mpol_rebind_mm+0x249/0x370 mm/mempolicy.c:384
>>
>> The report doesn't seem to indicate where the uninit value resides in
>> the mempolicy object.
> 
> Yes, it doesn't and it's not trivial to do. The tool reports uses of
> unint _values_. Values don't necessary reside in memory. It can be a
> register, that come from another register that was calculated as a sum
> of two other values, which may come from a function argument, etc.

I see. BTW, the patch I sent will be picked up for testing, or does it
have to be in mmotm/linux-next first?