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.
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