On Thu, Apr 18, 2013 at 10:07:11AM +0300, Abel Gordon wrote:
>
>
> Gleb Natapov <gleb@xxxxxxxxxx> wrote on 18/04/2013 09:38:43 AM:
>
> > On Wed, Apr 17, 2013 at 08:07:40PM +0300, Abel Gordon wrote:
> > > Allocate a shadow vmcs used by the processor to shadow part of the
> fields
> > > stored in the software defined VMCS12 (let L1 access fields without
> causing
> > > exits). Note we keep a shadow vmcs only for the current vmcs12.
> > Once a vmcs12
> > > becomes non-current, its shadow vmcs is released.
> > >
> > >
> > > Signed-off-by: Abel Gordon <abelg@xxxxxxxxxx>
> > > ---
> > > arch/x86/kvm/vmx.c | 12 ++++++++++++
> > > 1 file changed, 12 insertions(+)
> > >
> > > --- .before/arch/x86/kvm/vmx.c 2013-04-17 19:58:32.000000000 +0300
> > > +++ .after/arch/x86/kvm/vmx.c 2013-04-17 19:58:32.000000000 +0300
> > > @@ -355,6 +355,7 @@ struct nested_vmx {
> > > /* The host-usable pointer to the above */
> > > struct page *current_vmcs12_page;
> > > struct vmcs12 *current_vmcs12;
> > > + struct vmcs *current_shadow_vmcs;
> > >
> > > /* vmcs02_list cache of VMCSs recently used to run L2 guests */
> > > struct list_head vmcs02_pool;
> > > @@ -5517,6 +5518,7 @@ static int handle_vmon(struct kvm_vcpu *
> > > {
> > > struct kvm_segment cs;
> > > struct vcpu_vmx *vmx = to_vmx(vcpu);
> > > + struct vmcs *shadow_vmcs;
> > >
> > > /* The Intel VMX Instruction Reference lists a bunch of bits that
> > > * are prerequisite to running VMXON, most notably cr4.VMXE must be
> > > @@ -5540,6 +5542,16 @@ static int handle_vmon(struct kvm_vcpu *
> > > kvm_inject_gp(vcpu, 0);
> > > return 1;
> > > }
> > > + if (enable_shadow_vmcs) {
> > > + shadow_vmcs = alloc_vmcs();
> > > + if (!shadow_vmcs)
> > > + return -ENOMEM;
> > > + /* mark vmcs as shadow */
> > > + shadow_vmcs->revision_id |= (1u << 31);
> > > + /* init shadow vmcs */
> > > + vmcs_clear(shadow_vmcs);
> > > + vmx->nested.current_shadow_vmcs = shadow_vmcs;
> > > + }
> > >
> > Guest can ddos host by calling vmxon repeatedly causing host to leak
> > memory. This point to a bug in vmxon implementation. vmxon should call
> > nested_vmx_failInvalid() if (vmx->nested.vmxon).
>
> Good point. I just checked the spec (VMXON pseudo-code) to verify
> the right emulation:
> According to the pseudo-code we should:
> ELSE VMfail(“VMXON executed in VMX root operation”) which means:
>
> VMfail(ErrorNumber):
> IF VMCS pointer is valid
> THEN VMfailValid(ErrorNumber);
> ELSE VMfailInvalid;
> FI;
>
>
> So, I'll call nested_vmx_failValid if nested.current_vmptr != -1ull
> Otherwise, I'll call nested_vmx_failInvalid.
>
Just call nested_vmx_failValid(). It does that internally.
--
Gleb.
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