Re: [PATCH RFC 00/10] Intel EPT-Based Sub-page Write Protection Support.

[Mihai DonÈu]

On Wed, 2017-10-18 at 11:35 +0200, Paolo Bonzini wrote:
> On 16/10/2017 02:08, Yi Zhang wrote:
> > > And the introspection facility by Mihai uses a completely
> > > different API for the introspector, based on sockets rather than ioctls.
> > > So I'm not sure this is the right API at all.
> > 
> > Currently,  We only block the write access, As far as I know an example,
> > we now using it in a security daemon:
> 
> Understood.  However, I think QEMU is the wrong place to set this up.
> 
> If the kernel wants to protect _itself_, it should use a hypercall.  If
> an introspector appliance wants to protect the guest kernel, it should
> use the socket that connects it to the hypervisor.

We have been looking at using SPP for VMI for quite some time. If a
guest kernel will be able to control it (can it do so with EPT?) then
it would be useful a simple switch that disables this ability, as an
introspector wouldn't want the guest is trying to protect to interfere
with it.

Also, if Intel doesn't have a specific use case for it that requires
separate access to SPP control, then maybe we can fold it into the VMI 
API we are working on?

Thanks,

> > Consider It has a server which launching in the host user-space, and a
> > client launching in the guest kernel. Yes, they are communicate with
> > sockets. The guest kernel wanna protect a special area to prevent all
> > the process including the kernel itself modify this area. the client
> > could send the guest physical address via the security socket to server
> > side, and server would update these protection into KVM. Thus, all the
> > write access in a guest specific area will be blocked.
> > 
> > Now the implementation only on the second half(maybe third ^_^) of this
> > example: 'How kvm set the write-protect into a specific GFN?'
> > 
> > Maybe a user space tools which use ioctl let kvm mmu update the
> > write-protection is a better choice.

-- 
Mihai DonÈu