Re: [Xen-devel] [PATCH 3/3 V3] XSA-60 security hole: cr0.cd handling

["Liu, Jinsong" <jinsong.liu@xxxxxxxxx>]

Liu, Jinsong wrote:
> Jan Beulich wrote:
>>>>> "Nakajima, Jun" <jun.nakajima@xxxxxxxxx> 10/23/13 6:29 PM >>>
>>> On Tue, Oct 22, 2013 at 7:55 AM, Jan Beulich <JBeulich@xxxxxxxx>
>>> wrote:
>>>>>>> On 21.10.13 at 17:55, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>
>>>>>>> wrote:
>>>>> From 4ff1e2955f67954e60562b29a00adea89e5b93ae Mon Sep 17 00:00:00
>>>>> 2001 From: Liu Jinsong <jinsong.liu@xxxxxxxxx>
>>>>> Date: Thu, 17 Oct 2013 05:49:23 +0800
>>>>> Subject: [PATCH 3/3 V3] XSA-60 security hole: cr0.cd handling
>>>>> 
>>>>> This patch solves XSA-60 security hole:
>>>>> 1. For guest w/o VT-d, and for guest with VT-d but snooped, Xen
>>>>> need do nothing, since hardware snoop mechanism has ensured cache
>>>>> coherency. 
>>>>> 
>>>>> 2. For guest with VT-d but non-snooped, cache coherency can not be
>>>>> guaranteed by h/w snoop, therefore it need emulate UC type to
>>>>> guest: 
>>>>> 2.1). if it works w/ Intel EPT, set guest IA32_PAT fields as UC so
>>>>> that guest memory type are all UC.
>>> 
>>> Can you make sure that "setting guest IA32_PAT fields as UC" doesn't
>>> have a conflict with the existing (other) settings done by the
>>> guest? 
>> 
>> I don't think I understand the question, and I also don't think I'm
>> the right addressee (I think you meant to send this to Jinsong and
>> only Cc me). 
>> 
>> Jan
> 
> Maybe Jun's concern is 'guest PAT (real pat of vmcs which take
> effect, not nominal guest_pat) should be identical among all physical
> processors which run vcpus of that guest', am I right, Jun?  
> 
> One thing I'm not sure is, per Intel SDM (8.7.4 of volume 3), the PAT
> MSR settings must be the same for all processors in a system.
> However, Xen obviously doesn't satisfy this requirement: PAT of the
> cpus running vmm context (50100070406) is not identical to PAT of the
> cpus running guest context (take rhel6.4 guest as example, it's
> 7010600070106) -- practically it works fine.

Or, PAT requirement under virtualization would better be 'PAT MSR settings must 
be the same for all processors of a domain (take vmm as a special domain)'? 
otherwise IA32_PAT fields of vmcs is pointless.

Anyway, we'd better change our patch from per-vcpu PAT emulation to per-domain 
PAT emulation. Does it make sense, Jun?

Thanks,
Jinsong
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