Re: KMSAN: uninit-value in mpol_rebind_mm

[Dmitry Vyukov]

On Fri, Jan 4, 2019 at 9:50 AM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>
> On 1/3/19 9:42 AM, Dmitry Vyukov wrote:
> > On Thu, Jan 3, 2019 at 9:36 AM Vlastimil Babka <vbabka@xxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> >>>
> >>> ==================================================================
> >>> 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?

It needs to be in upstream tree. Since KMSAN is not upstream, we have
only 1 branch that is based on upstream and is periodically rebased:
https://github.com/google/kmsan
If the bug would have a repro, then we could ask syzbot to test this
patch on top of KMSAN tree. But unfortunately it doesn't.