[PATCH v2 3/9] KVM: x86: Inter privilage level ret emulation is not implemeneted

Nadav Amit
2014-06-18T14:19:38Z

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

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
arch/x86/kvm/emulate.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 3c8d867..0183350 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2019,6 +2019,7 @@ 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)
@@ -2028,6 +2029,9 @@ 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-privilage 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;
}
--
1.9.1