ARM validator: fix sandbox escape with SP update at the end of the last bundle

src/trusted/validator_arm/validator.cc

Index: src/trusted/validator_arm/validator.cc
diff --git a/src/trusted/validator_arm/validator.cc b/src/trusted/validator_arm/validator.cc
index 2e19a8dd495bad2aa33607866880432055cf61ed..e2691706db241a0856de13ad925437b8347f39fe 100644
--- a/src/trusted/validator_arm/validator.cc
+++ b/src/trusted/validator_arm/validator.cc
@@ -721,6 +721,12 @@ bool SfiValidator::validate_fallthrough(const CodeSegment& segment,
     pred.Copy(inst);
   }
 
+  // Validate the last instruction, paired with a nop.
+  const Instruction nop(nacl_arm_dec::kNop);
+  DecodedInstruction one_past_end(segment.end_addr(), nop,
+                                  decode_state_.decode(nop));
+  complete_success &= apply_patterns(pred, one_past_end, critical, out);
+
   return complete_success;
 }