[PATCH 3.10 28/55] KVM: x86: Inter-privilege level ret emulation is not implemeneted

Greg Kroah-Hartman
2014-09-03T23:40:45Z

From: Nadav Amit <namit@cs.technion.ac.il>

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/emulate.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2209,6 +2209,7 @@ 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)
@@ -2218,6 +2219,9 @@ 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;
}