KVM: x86: Inter-privilege level ret emulation is not implemeneted

commit 9e8919ae793f4edfaa29694a70f71a515ae9942a upstream.

Return unhandlable error on inter-privilege level ret instruction.  This is
since the current emulation does not check the privilege level correctly when
loading the CS, and does not pop RSP/SS as needed.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index f5302da..638cab5 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1818,6 +1818,7 @@ static int em_ret_far(struct x86_emulate_ctxt *ctxt)
 {
        int rc;
        unsigned long cs;
+       int cpl = ctxt->ops->cpl(ctxt);
 
        rc = emulate_pop(ctxt, &ctxt->_eip, ctxt->op_bytes);
        if (rc != X86EMUL_CONTINUE)
@@ -1827,6 +1828,9 @@ static int em_ret_far(struct x86_emulate_ctxt *ctxt)
        rc = emulate_pop(ctxt, &cs, ctxt->op_bytes);
        if (rc != X86EMUL_CONTINUE)
                return rc;
+       /* Outer-privilege level return is not implemented */
+       if (ctxt->mode >= X86EMUL_MODE_PROT16 && (cs & 3) > cpl)
+               return X86EMUL_UNHANDLEABLE;
        rc = load_segment_descriptor(ctxt, (u16)cs, VCPU_SREG_CS);
        return rc;
 }