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

[Andy Lutomirski <luto@kernel.org>]

On Thu, Jun 15, 2017 at 8:46 PM, Huang, Kai <kai.huang@linux.intel.com> wrote:
>
>
> On 6/13/2017 11:00 AM, Andy Lutomirski wrote:
>>
>> On Mon, Jun 12, 2017 at 3:08 PM, Huang, Kai <kai.huang@linux.intel.com>
>> wrote:
>>>
>>>
>>> I don't know whether SGX driver will have restrict on running
>>> provisioning
>>> enclave. In my understanding provisioning enclave is always from Intel.
>>> However I am not expert here and probably be wrong. Can you point out
>>> *exactly* what restricts in host must/should be applied to guest so that
>>> Jarkko can know whether he will support those restricts or not? Otherwise
>>> I
>>> don't think we even need to talk about this topic at current stage.
>>>
>>
>> The whole point is that I don't know.  But here are two types of
>> restriction I can imagine demand for:
>>
>> 1. Only a particular approved provisioning enclave may run (be it
>> Intel's or otherwise -- with a non-Intel LE, I think you can launch a
>> non-Intel provisioning enclave).  This would be done to restrict what
>> types of remote attestation can be done. (Intel supplies a remote
>> attestation service that uses some contractual policy that I don't
>> know.  Maybe a system owner wants a different policy applied to ISVs.)
>>   Imposing this policy on guests more or less requires filtering EINIT.
>
>
> Hi Andy,
>
> Sorry for late reply.
>
> What is the issue if host and guest run provisioning enclave from different
> vendor, for example, host runs intel's provisioning enclave, and guest runs
> other vendor's provisioning enclave? Or different guests run provisioning
> enclaves from different vendors?

There's no issue unless someone has tried to impose a policy.  There
is clearly at least some interest in having policies that affect what
enclaves can run -- otherwise there wouldn't be LEs in the first
place.

>
> One reason I am asking is that, on Xen (where we don't have concept of
> *host*), it's likely that we won't apply any policy at Xen hypervisor at
> all, and guests will be able to run any enclave from any signer as their
> wish.

That seems entirely reasonable.  Someone may eventually ask Xen to add
support for SGX enclave restrictions, in which case you'll either have
to tell them that it won't happen or implement it.

>
> Sorry that I don't understand (or kind of forgot) the issues here.
>
>>
>> 2. For kiosk-ish or single-purpose applications, I can imagine that
>> you would want to allow a specific list of enclave signers or even
>> enclave hashes. Maybe you would allow exactly one enclave hash.  You
>> could kludge this up with a restrictive LE policy, but you could also
>> do it for real by implementing the specific restriction in the kernel.
>> Then you'd want to impose it on the guest, and you'd do it by
>> filtering EINIT.
>
> Assuming the enclave hash means measurement of enclave, and assuming we have
> a policy that we only allow enclave from one signer to run, would you also
> elaborate the issue that, if host and guest run enclaves from different
> signer? If host has such policy, and we are allowing creating guests on such
> host, I think that typically we will have the same policy in the guest

Yes, I presume this too, but.

> (vetted by guest's kernel). The owner of that host should be aware of the
> risk (if there's any) by creating guest and run enclave inside it.

No.  The host does not trust the guest in general.  If the host has a
policy that the only enclave that shall run is X, that doesn't mean
that the host shall reject all enclaves requested by the normal
userspace API except X but that, if /dev/kvm is used, then the user is
magically trusted to not load a guest that fails to respect the host
policy.  It means that the only enclave that shall run is X regardless
of what interface is used.  The host must only allow X to be loaded by
its userspace and the host must only allow X to be loaded by a guest.