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

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Date:	Thu, 7 Apr 2016 11:08:18 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	David Matlack <dmatlack@...gle.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 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. :)

Paolo