kvm: nVMX: Don't allow L2 to access the hardware CR8

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>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 0920499..8e1ae71 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10525,6 +10525,11 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
        if (exec_control & CPU_BASED_TPR_SHADOW) {
                vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, -1ull);
                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
        }
 
        /*