Re: [PATCH] KVM: VMX: mark unusable segment as nonpresent

[Gleb Natapov <gleb@redhat.com>]

On Tue, Jul 02, 2013 at 10:15:54AM +0200, Paolo Bonzini wrote:
> Il 28/06/2013 12:17, Gleb Natapov ha scritto:
> > Some userspaces do not preserve unusable property. Since usable
> > segment has to be present according to VMX spec we can use present
> > property to amend userspace bug by making unusable segment always
> > nonpresent. vmx_segment_access_rights() already marks nonpresent segment
> > as unusable.
> > 
> > Cc: stable@vger.kernel.org # 3.9+
> > Reported-by: Stefan Pietsch <stefan.pietsch@lsexperts.de>
> > Tested-by: Stefan Pietsch <stefan.pietsch@lsexperts.de>
> > Signed-off-by: Gleb Natapov <gleb@redhat.com>
> > 
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index 260a919..5402c94 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -3399,15 +3399,22 @@ static void vmx_get_segment(struct kvm_vcpu *vcpu,
> >  	var->limit = vmx_read_guest_seg_limit(vmx, seg);
> >  	var->selector = vmx_read_guest_seg_selector(vmx, seg);
> >  	ar = vmx_read_guest_seg_ar(vmx, seg);
> > +	var->unusable = (ar >> 16) & 1;
> >  	var->type = ar & 15;
> >  	var->s = (ar >> 4) & 1;
> >  	var->dpl = (ar >> 5) & 3;
> > -	var->present = (ar >> 7) & 1;
> > +	/*
> > +	 * Some userspaces do not preserve unusable property. Since usable
> > +	 * segment has to be present according to VMX spec we can use present
> > +	 * property to amend userspace bug by making unusable segment always
> > +	 * nonpresent. vmx_segment_access_rights() already marks nonpresent
> > +	 * segment as unusable.
> > +	 */
> > +	var->present = !var->unusable;
> >  	var->avl = (ar >> 12) & 1;
> >  	var->l = (ar >> 13) & 1;
> >  	var->db = (ar >> 14) & 1;
> >  	var->g = (ar >> 15) & 1;
> > -	var->unusable = (ar >> 16) & 1;
> >  }
> >  
> >  static u64 vmx_get_segment_base(struct kvm_vcpu *vcpu, int seg)
> > --
> > 			Gleb.
> > 
> 
> Looks good, but for now I'm leaving it out of the 3.11 pull request.
> Applied to queue.
> 
It affects people so lets target it to 3.10/3.9-stable.

--
			Gleb.