[PATCH 4.4 25/41] kvm: nVMX: Dont allow L2 to access the hardware CR8

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jim Mattson <jmattson@google.com>

commit 51aa68e7d57e3217192d88ce90fd5b8ef29ec94f upstream.

If L1 does not specify the "use TPR shadow" VM-execution control in
vmcs12, then L0 must specify the "CR8-load exiting" and "CR8-store
exiting" VM-execution controls in vmcs02. Failure to do so will give
the L2 VM unrestricted read/write access to the hardware CR8.

This fixes CVE-2017-12154.

Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/kvm/vmx.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -9683,6 +9683,11 @@ static void prepare_vmcs02(struct kvm_vc
 		vmcs_write64(VIRTUAL_APIC_PAGE_ADDR,
 				page_to_phys(vmx->nested.virtual_apic_page));
 		vmcs_write32(TPR_THRESHOLD, vmcs12->tpr_threshold);
+	} else {
+#ifdef CONFIG_X86_64
+		exec_control |= CPU_BASED_CR8_LOAD_EXITING |
+				CPU_BASED_CR8_STORE_EXITING;
+#endif
 	}
 
 	if (cpu_has_vmx_msr_bitmap() &&