[PATCH 3.2 001/131] KVM: x86: Inter-privilege level ret emulation is not implemeneted

[Ben Hutchings]

3.2.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Nadav Amit <namit@xxxxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/kvm/emulate.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1818,6 +1818,7 @@ static int em_ret_far(struct x86_emulate
 {
 	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
 	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;
 }

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