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

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Date:   Fri, 20 Oct 2017 16:47:15 +0800
From:   Yi Zhang <yi.z.zhang@...ux.intel.com>
To:     Mihai Donțu <mdontu@...defender.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH RFC 00/10] Intel EPT-Based Sub-page Write Protection
 Support.

On 2017-10-18 at 17:13:18 +0300, Mihai Donțu wrote:
> 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.

Could you mind to provide more information and history about your
investigation?

> 
> 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?

That's totally Excellent as we really don't have a specific user case at
this time.
BTW, I have already submit the SPP implementation draft in Xen side.
when you got some time, you can take a look at if that match your
requirement.

> 
> 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 Donțu
>