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

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Tue, Jun 13, 2017 at 09:57:18PM +0300, Jarkko Sakkinen wrote:
> On Mon, Jun 12, 2017 at 09:53:41PM +1200, Huang, Kai wrote:
> > > > This is simple, we simply won't allow guest to choose its own
> > > > IA32_SGXLEPUBKEYHASHn by specifying 'lehash' value in Qemu parameter when
> > > > creating the guest.
> > > 
> > > Why not? You could have virtual MSRs and ask host LE to generate token
> > > if they match to modulus.
> > 
> > The guest has its own LE running inside, and guest's LE will generate token
> > for enclaves in guest. The host will not generate token for guest in any
> > circumstances, because this is totally guest's behavior.
> 
> Why can't host LE generate the token without guest knowning it and
> supply it with EINIT?
> > > Seriously sounds like a stupid constraint or I'm not getting something
> > > (which also might be the case). If you anyway trap EINIT, you could
> > > create a special case for guest LE.
> > 
> > This is not constraint, but KVM has to emulate hardware correctly. For this
> > part please see my explanation above.
> 
> I'm being now totally honest to your: your explanation makes absolutely
> zero sense to me. You don't need a 1000+ words to explain the scenarios
> where "host as a delegate LE" approach would go wrong.
> 
> Please just pinpoint the scenarios where it goes wrong. I'll ignore
> the text below.
> 
> /Jarkko

When I've been reading this discussion the biggest lesson for me has
been that this is a new argument for having in-kernel LE in addition
to what Andy has stated before: the MSRs *never* need to be updated on
behalf of the guest.

/Jarkko