Re: [intel-sgx-kernel-dev] [PATCH 08/10] kvm: vmx: add guest's IA32_SGXLEPUBKEYHASHn runtime switch support

From: "Huang, Kai" <kai.huang@linux.intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>, Andy Lutomirski <luto@kernel.org>
Cc: Kai Huang <kaih.linux@gmail.com>,
	Radim Krcmar <rkrcmar@redhat.com>, kvm list <kvm@vger.kernel.org>,
	"intel-sgx-kernel-dev@lists.01.org"
	<intel-sgx-kernel-dev@ml01.01.org>,
	haim.cohen@intel.com
Subject: Re: [intel-sgx-kernel-dev] [PATCH 08/10] kvm: vmx: add guest's IA32_SGXLEPUBKEYHASHn runtime switch support
Date: Thu, 18 May 2017 19:54:32 +1200	[thread overview]
Message-ID: <0ab082cb-c13d-b62e-9662-6fd32e36d1ac@linux.intel.com> (raw)
In-Reply-To: <0d730428-44fa-67b3-02f4-bd5223a6ec19@redhat.com>

On 5/17/2017 2:21 AM, Paolo Bonzini wrote:
>
>
> On 16/05/2017 02:48, Huang, Kai wrote:
>>
>>
>> If host only allows one single LE to run, KVM can add a restrict that
>> only allows to create KVM guest with runtime change to
>> IA32_SGXLEPUBKEYHASHn disabled, so that only host allowed (single) hash
>> can be used by guest. From guest's view, it simply has
>> IA32_FEATURE_CONTROL[bit17] cleared and has IA32_SGXLEPUBKEYHASHn with
>> default value to be host allowed (single) hash.
>>
>> If host allows several LEs (not but everything), and if we create guest
>> with 'lewr', then the behavior is not consistent with HW behavior, as
>> from guest's hardware's point of view, we can actually run any LE but we
>> have to tell guest that you are only allowed to change
>> IA32_SGXLEPUBKEYHASHn to some specific values. One compromise solution
>> is we don't allow to create guest with 'lewr' specified, and at the
>> meantime, only allow to create guest with host approved hashes specified
>> in 'lehash'. This will make guest's behavior consistent to HW behavior
>> but only allows guest to run one LE (which is specified by 'lehash' when
>> guest is created).
>>
>> I'd like to hear comments from you guys.
>>
>> Paolo, do you also have comments here from KVM's side?
>
> I would start with read-only LE hash (same as the host), which is a
> valid configuration anyway.  Then later we can trap EINIT to emulate
> IA32_SGXLEPUBKEYHASHn.

You mean we can start with creating guest without Qemu 'lewr' parameter 
support, and always disallowing guest to change IA32_SGXLEPUBKEYHASHn?
Even in this way, KVM still needs to emulate IA32_SGXLEPUBKEYHASHn (just 
allow MSR reading but not writing), and write guest's value to physical 
MSRs when running guest (trapping EINIT and write MSRs during EINIT is 
really just performance optimization). Because host can run multiple LEs 
and change MSRs. Your suggestion only works when runtime change to 
IA32_SGXLEPUBKEYHASHn is disabled on host (meaning physical machine).

Thanks,
-Kai
>
> Paolo
>