Re: [Xen-devel] [PATCH 1/4] x86/vmx: Don't leak host syscall MSR state into HVM guests

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/02/17 10:13, Jan Beulich wrote:
>>>> On 14.02.17 at 09:40, <kevin.tian@xxxxxxxxx> wrote:
>>>  From: Andrew Cooper [mailto:amc96@xxxxxxxxxxxxxxxx] On Behalf Of Andrew 
>>> Cooper
>>> Sent: Tuesday, February 14, 2017 4:19 PM
>>>
>>> On 14/02/2017 08:04, Tian, Kevin wrote:
>>>>> From: Andrew Cooper [mailto:amc96@xxxxxxxxxxxxxxxx] On Behalf Of Andrew
>>> Cooper
>>>>> Sent: Tuesday, February 14, 2017 3:59 PM
>>>>>
>>>>> On 14/02/2017 02:52, Tian, Kevin wrote:
>>>>>>> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
>>>>>>> Sent: Monday, February 13, 2017 10:32 PM
>>>>>>>
>>>>>>> hvm_hw_cpu->msr_flags is in fact the VMX dirty bitmap of MSRs needing 
>>>>>>> to be
>>>>>>> restored when switching into guest context.  It should never have been 
>>>>>>> part of
>>>>>>> the migration state to start with, and Xen must not make any decisions 
>>>>>>> based
>>>>>>> on the value seen during restore.
>>>>>>>
>>>>>>> Identify it as obsolete in the header files, consistently save it as 
>>>>>>> zero and
>>>>>>> ignore it on restore.
>>>>>>>
>>>>>>> The MSRs must be considered dirty during VMCS creation to cause the 
>>>>>>> proper
>>>>>>> defaults of 0 to be visible to the guest.
>>>>>>>
>>>>>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>>>> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>, with one small comment.
>>>>>>
>>>>>> the effect of this patch should be more than not leaking syscall MSR.
>>>>>> what about making the subject clearer when check-in?
>>>>> What other effects do you think are going on here?  Yes, we now context
>>>>> switch the MSRs right from the start of the domain, but that is
>>>>> necessary to avoid leaking them.
>>>>>
>>>> If just looking at this patch, it's for general MSR save/restore policy,
>>>> nothing specific to syscall MSR.
>>> The only three MSRs which use this infrastructure are LSTAR, STAR and
>>> FMASK.  What if I were to clarify that in the first paragraph?
>> I meant the subject line (talk about syscall MSR leakage) mismatches the 
>> commit message (for general MSR load)
> I'm with Andrew here: The title seems perfectly fine to me, considering
> that the generic mechanism is only used for the syscall MSRs. Hence I
> would think his offer to clarify the change in the first paragraph of the
> commit message ought to suffice. Otherwise, may I ask that you make
> a concrete suggestion as to what you'd like to see?

Kevin: Do you have any other concerns?

~Andrew

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