Commit 4873041d authored Mar 09, 2020 by Vitaly Kuznetsov Committed by Greg Kroah-Hartman Mar 18, 2020

KVM: nVMX: avoid NULL pointer dereference with incorrect EVMCS GPAs



commit 95fa10103dabc38be5de8efdfced5e67576ed896 upstream.

When an EVMCS enabled L1 guest on KVM will tries doing enlightened VMEnter
with EVMCS GPA = 0 the host crashes because the

evmcs_gpa != vmx->nested.hv_evmcs_vmptr

condition in nested_vmx_handle_enlightened_vmptrld() will evaluate to
false (as nested.hv_evmcs_vmptr is zeroed after init). The crash will
happen on vmx->nested.hv_evmcs pointer dereference.

Another problematic EVMCS ptr value is '-1' but it only causes host crash
after nested_release_evmcs() invocation. The problem is exactly the same as
with '0', we mistakenly think that the EVMCS pointer hasn't changed and
thus nested.hv_evmcs_vmptr is valid.

Resolve the issue by adding an additional !vmx->nested.hv_evmcs
check to nested_vmx_handle_enlightened_vmptrld(), this way we will
always be trying kvm_vcpu_map() when nested.hv_evmcs is NULL
and this is supposed to catch all invalid EVMCS GPAs.

Also, initialize hv_evmcs_vmptr to '0' in nested_release_evmcs()
to be consistent with initialization where we don't currently
set hv_evmcs_vmptr to '-1'.

Cc: stable@vger.kernel.org
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 84c6ce00

arch/x86/kvm/vmx/nested.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -223,7 +223,7 @@ static inline void nested_release_evmcs(struct kvm_vcpu *vcpu)
		return;

		kvm_vcpu_unmap(vcpu, &vmx->nested.hv_evmcs_map, true);
		vmx->nested.hv_evmcs_vmptr = -1ull;
		vmx->nested.hv_evmcs_vmptr = 0;
		vmx->nested.hv_evmcs = NULL;
		}

		@@ -1828,7 +1828,8 @@ static int nested_vmx_handle_enlightened_vmptrld(struct kvm_vcpu *vcpu,
		if (!nested_enlightened_vmentry(vcpu, &evmcs_gpa))
		return 1;

		if (unlikely(evmcs_gpa != vmx->nested.hv_evmcs_vmptr)) {
		if (unlikely(!vmx->nested.hv_evmcs \|\|
		evmcs_gpa != vmx->nested.hv_evmcs_vmptr)) {
		if (!vmx->nested.hv_evmcs)
		vmx->nested.current_vmptr = -1ull;