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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/02/2017 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.

~Andrew

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