[PATCH 2/3] KVM: x86: Emulator support for #UD on CPL>0

Nadav Amit
2014-06-18T14:19:58Z

Certain instructions (e.g., mwait and monitor) cause a #UD exception when they
are executed in privilaged mode. This is in contrast to the regular privilaged
instructions which cause #GP. In order not to mess with SVM interception of
mwait and monitor which assumes privilage level assertions take place before
interception, a flag has been added.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
arch/x86/kvm/emulate.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index f90194d..ef7a5a0 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -163,6 +163,7 @@
#define SrcWrite ((u64)1 << 46) /* Write back src operand */
#define NoMod ((u64)1 << 47) /* Mod field is ignored */
#define NoBigReal ((u64)1 << 48) /* No big real mode */
+#define UDOnPriv ((u64)1 << 49) /* #UD instead of #GP on CPL > 0 */

#define DstXacc (DstAccLo | SrcAccHi | SrcWrite)

@@ -4560,7 +4561,10 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)

/* Privileged instruction can be executed only in CPL=0 */
if ((ctxt->d & Priv) && ops->cpl(ctxt)) {
- rc = emulate_gp(ctxt, 0);
+ if (ctxt->d & UDOnPriv)
+ rc = emulate_ud(ctxt);
+ else
+ rc = emulate_gp(ctxt, 0);
goto done;
}

--
1.9.1