KVM: emulator: fix real mode segment checks in address linearization

In real mode CS register is writable, so do not #GP on write.
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/emulate.c

@@ -677,8 +677,9 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
 						addr.seg);
 		if (!usable)
 			goto bad;
-		/* code segment or read-only data segment */
-		if (((desc.type & 8) || !(desc.type & 2)) && write)
+		/* code segment in protected mode or read-only data segment */
+		if ((((ctxt->mode != X86EMUL_MODE_REAL) && (desc.type & 8))
+					|| !(desc.type & 2)) && write)
 			goto bad;
 		/* unreadable code segment */
 		if (!fetch && (desc.type & 8) && !(desc.type & 2))