Change BKPT and UDF encodings on ARM.

src/trusted/validator_arm/actual_classes.cc

Index: src/trusted/validator_arm/actual_classes.cc
diff --git a/src/trusted/validator_arm/actual_classes.cc b/src/trusted/validator_arm/actual_classes.cc
index 505a3ef94fb23f15d640083cde8993ecdd470aa7..f190e772ba9652496fdf6a572fd7a229acda02c9 100644
--- a/src/trusted/validator_arm/actual_classes.cc
+++ b/src/trusted/validator_arm/actual_classes.cc
@@ -528,22 +528,34 @@ RegisterList EffectiveNoOp::defs(Instruction i) const {
   return RegisterList();
 }
 
-// Roadblock
-SafetyLevel Roadblock::safety(Instruction i) const {
-  UNREFERENCED_PARAMETER(i);
-  return MAY_BE_SAFE;
+// PermanentlyUndefined
+SafetyLevel PermanentlyUndefined::safety(Instruction i) const {
+  // Restrict UDF's encoding to values we've chosen as safe.
+  if ((i.Bits(31, 0) == kHaltFill) ||
+      (i.Bits(31, 0) == kAbortNow))
+    return MAY_BE_SAFE;
+  return FORBIDDEN_OPERANDS;
 }
 
-RegisterList Roadblock::defs(Instruction i) const {
+RegisterList PermanentlyUndefined::defs(Instruction i) const {
   UNREFERENCED_PARAMETER(i);
   return RegisterList();
 }
 
 // Breakpoint
 SafetyLevel Breakpoint::safety(Instruction i) const {
-  return i.GetCondition() == Instruction::AL
-      ? MAY_BE_SAFE
-      : UNPREDICTABLE;
+  if (i.GetCondition() != Instruction::AL)
+    return UNPREDICTABLE;
+  // Restrict BKPT's encoding to values we've chosen as safe.
+  if ((i.Bits(31, 0) == kLiteralPoolHeadInstruction) ||
+      (i.Bits(31, 0) == kBreakpoint))
+    return MAY_BE_SAFE;
+  return FORBIDDEN_OPERANDS;
+}
+
+RegisterList Breakpoint::defs(Instruction i) const {
+  UNREFERENCED_PARAMETER(i);
+  return RegisterList();
 }
 
 bool Breakpoint::is_literal_pool_head(const Instruction i) const {