KVM: x86 emulator: Forbid modifying CS segment register by mov instruction

commit 8b9f44140bc4afd2698413cd9960c3912168ee91 upstream.

Inject #UD if guest attempts to do so. This is in accordance to Intel
SDM.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index f4e2a49513f1..3b9aca42cd30 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1987,6 +1987,12 @@ special_insn:
                 int err;
 
                 sel = c->src.val;
+
+                if (c->modrm_reg == VCPU_SREG_CS) {
+                        kvm_queue_exception(ctxt->vcpu, UD_VECTOR);
+                        goto done;
+                }
+
                 if (c->modrm_reg == VCPU_SREG_SS)
                         toggle_interruptibility(ctxt, X86_SHADOW_INT_MOV_SS);