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

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Message-ID: <CALzav=e_e9qV5+csaQOT0fmi8U4_VGa_9thg=D-V=v12wKbC-w@mail.gmail.com>
Date:	Thu, 7 Apr 2016 11:18:32 -0700
From:	David Matlack <dmatlack@...gle.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	kvm list <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>, stable@...r.kernel.org
Subject: Re: [PATCH] kvm: x86: do not leak guest xcr0 into host interrupt handlers

On Thu, Apr 7, 2016 at 2:08 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
>
> On 05/04/2016 17:56, David Matlack wrote:
>> On Tue, Apr 5, 2016 at 4:28 AM, Paolo Bonzini <pbonzini@...hat.com> 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
>