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Date: Wed, 3 Aug 2016 01:44:38 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Ksummit-discuss] late self-nomination
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On Tue, Aug 02, 2016 at 03:00:13PM -0400, Paolo Bonzini wrote:
> > > On x86 with VMX, the EPT page tables have separate R, W, and X bits.
> > > If a hypervisor were to limit the guest physical address space to the
> > > lower half (high bit always clear) and then alias all of it with the
> > > high guest physical address bit set and R clear, then the guest could
> > > use the high physical address bit as an effective R bit.  That would
> > > allow PROT_WRITE, PROT_EXEC, and PROT_WRITE|PROT_EXEC mappings to work
> > > without granting read access.
> > > 
> > > Doing this would provide some protection against attacks that use a
> > > wild read to scan for code or data structures at otherwise
> > > unpredictable addresses or to blindly search for ROP gadgets.
> > 
> > Thanks - I expect we'll discuss this topic with other kvm folks quite a
> > bit on the kvm forum end of August, as well.
> 
> I won't be able to attend kernel summit (I haven't nominated me for this
> reason) so I support Michael's presence!
> 
> Paolo

I didn't realize. In that case I might be able to also give some
kind of summary from the kvm forum as well, if there's interest.

-- 
MST