Re: kvm/arm64: use-after-free in kvm_unmap_hva_handler/unmap_stage2_pmds

[Andrey Konovalov]

On Thu, Apr 13, 2017 at 11:34 AM, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> On Wed, Apr 12, 2017 at 08:51:31PM +0200, Andrey Konovalov wrote:
>> On Wed, Apr 12, 2017 at 8:43 PM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
>> > On 12/04/17 17:19, Andrey Konovalov wrote:
>
>> >> I now have a way to reproduce it, so I can test proposed patches. I
>> >> don't have a simple C reproducer though.
>> >>
>> >> The bug happens when the following syzkaller program is executed:
>> >>
>> >> mmap(&(0x7f0000000000/0xc000)=nil, (0xc000), 0x3, 0x32, 0xffffffffffffffff, 0x0)
>> >> unshare(0x400)
>> >> perf_event_open(&(0x7f000002f000-0x78)={0x1, 0x78, 0x0, 0x0, 0x0, 0x0,
>> >> 0x0, 0x6, 0x0, 0x0, 0xd34, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
>> >> 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, 0x0, 0xffffffff,
>> >> 0xffffffffffffffff, 0x0)
>> >> r0 = openat$kvm(0xffffffffffffff9c,
>> >> &(0x7f000000c000-0x9)="2f6465762f6b766d00", 0x0, 0x0)
>> >> ioctl$TIOCSBRK(0xffffffffffffffff, 0x5427)
>> >> r1 = ioctl$KVM_CREATE_VM(r0, 0xae01, 0x0)
>> >> syz_kvm_setup_cpu$arm64(r1, 0xffffffffffffffff,
>> >> &(0x7f0000dc6000/0x18000)=nil, &(0x7f000000c000)=[{0x0,
>> >> &(0x7f000000c000)="5ba3c16f533efbed09f8221253c73763327fadce2371813b45dd7f7982f84a873e4ae89a6c2bd1af83a6024c36a1ff518318",
>> >> 0x32}], 0x1, 0x0, &(0x7f000000d000-0x10)=[@featur2={0x1, 0x3}], 0x1)
>> >
>> > Is that the only thing the program does? Or is there anything running in
>> > parallel?
>>
>> These calls are executed repeatedly and in random order. That's all.
>>
>> Except that I'm running the reproducer on a real arm board, so there's
>> probably a bunch of stuff going on besides these calls.
>
> I had a go at reproducing this on an arm64 board following [1], but so
> far I've had no luck. I've dumped the above into syz-kvm-bug, and I'm
> trying to reproduce the issue with:
>
>         PATH=$PATH:$(pwd)/bin syz-execprog \
>                 -executor $(pwd)/bin/syz-executor \
>                 -cover=0 -repeat=0 -procs 16 \
>                 syz-kvm-bug
>
> Just to check, is that the correct way to reproduce the problem with the
> above log?

Hi Mark,

You assume that you have KASAN enabled.

Since a few unintended line breaks were added in the email, here's the
program in plaintext:
https://gist.githubusercontent.com/xairy/69864355b5a64f74e7cb445b7325a7df/raw/bdbbbf177dbea13eac0a5ddfa9c3e6c32695b13b/kvm-arm-uaf-log

I run it as:
# ./syz-execprog -repeat=0 -collide=false -sandbox=namespace ./kvm-arm-uaf-log

And it takes less than a second to trigger the bug.

Thanks!

>
> How quickly does that reproduce the problem for you?
>
> Thanks,
> Mark.
>
> [1] https://github.com/google/syzkaller/wiki/How-to-execute-syzkaller-programs