kvm: nVMX: Enforce cpl=0 for VMX instructions

VMX instructions executed inside a L1 VM will always trigger a VM exit
even when executed with cpl 3. This means we must perform the
privilege check in software.

Fixes: 70f3aac964ae("kvm: nVMX: Remove superfluous VMX instruction fault checks")
Cc: stable@vger.kernel.org
Signed-off-by: Felix Wilhelm <fwilhelm@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 709de996f063..4bf1f9de9332 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -7905,6 +7905,12 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
                 return 1;
         }
 
+        /* CPL=0 must be checked manually. */
+        if (vmx_get_cpl(vcpu)) {
+                kvm_queue_exception(vcpu, UD_VECTOR);
+                return 1;
+        }
+
         if (vmx->nested.vmxon) {
                 nested_vmx_failValid(vcpu, VMXERR_VMXON_IN_VMX_ROOT_OPERATION);
                 return kvm_skip_emulated_instruction(vcpu);
@@ -7964,6 +7970,11 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
  */
 static int nested_vmx_check_permission(struct kvm_vcpu *vcpu)
 {
+        if (vmx_get_cpl(vcpu)) {
+                kvm_queue_exception(vcpu, UD_VECTOR);
+                return 0;
+        }
+
         if (!to_vmx(vcpu)->nested.vmxon) {
                 kvm_queue_exception(vcpu, UD_VECTOR);
                 return 0;
@@ -8283,7 +8294,7 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
                 if (get_vmx_mem_address(vcpu, exit_qualification,
                                 vmx_instruction_info, true, &gva))
                         return 1;
-                /* _system ok, as hardware has verified cpl=0 */
+                /* _system ok, nested_vmx_check_permission has verified cpl=0 */
                 kvm_write_guest_virt_system(&vcpu->arch.emulate_ctxt, gva,
                              &field_value, (is_long_mode(vcpu) ? 8 : 4), NULL);
         }
@@ -8448,7 +8459,7 @@ static int handle_vmptrst(struct kvm_vcpu *vcpu)
         if (get_vmx_mem_address(vcpu, exit_qualification,
                         vmx_instruction_info, true, &vmcs_gva))
                 return 1;
-        /* ok to use *_system, as hardware has verified cpl=0 */
+        /* *_system ok, nested_vmx_check_permission has verified cpl=0 */
         if (kvm_write_guest_virt_system(&vcpu->arch.emulate_ctxt, vmcs_gva,
                                  (void *)&to_vmx(vcpu)->nested.current_vmptr,
                                  sizeof(u64), &e)) {