Re: [PATCH] kvm: x86: do not leak guest xcr0 into host interrupt handlers

[David Matlack]

On Thu, Apr 7, 2016 at 2:08 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
>
> On 05/04/2016 17:56, David Matlack wrote:
>> On Tue, Apr 5, 2016 at 4:28 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>>>
>> ...
>>>
>>> While running my acceptance tests, in one case I got one CPU whose xcr0
>>> had leaked into the host.  This showed up as a SIGILL in strncasecmp's
>>> AVX code, and a simple program confirmed it:
>>>
>>>     $ cat xgetbv.c
>>>     #include <stdio.h>
>>>     int main(void)
>>>     {
>>>         unsigned xcr0_h, xcr0_l;
>>>         asm("xgetbv" : "=d"(xcr0_h), "=a"(xcr0_l) : "c"(0));
>>>         printf("%08x:%08x\n", xcr0_h, xcr0_l);
>>>     }
>>>     $ gcc xgetbv.c -O2
>>>     $ for i in `seq 0 55`; do echo $i `taskset -c $i ./a.out`; done|grep -v 007
>>>     19 00000000:00000003
>>>
>>> I'm going to rerun the tests without this patch, as it seems the most
>>> likely culprit, and leave it out of the pull request if they pass.
>>
>> Agreed this is a very likely culprit. I think I see one way the
>> guest's xcr0 can leak into the host.
>
> That's cancel_injection, right?  If it's just about moving the load call
> below, I can do that.  Hmm, I will even test that today. :)

Yes that's what I was thinking, move kvm_load_guest_xcr0 below that if.

Thank you :). Let me know how testing goes.

>
> Paolo
>