disable unpriv perf by default in user{,debug} builds

Bug: 29054680

Change-Id: If04bc63fc366006cde842a50b7c764f89d7449a6
diff --git a/core/main.mk b/core/main.mk
index 9866dff..bfa060c 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -376,6 +376,7 @@
 ifneq (,$(user_variant))
   # Target is secure in user builds.
   ADDITIONAL_DEFAULT_PROPERTIES += ro.secure=1
+  ADDITIONAL_DEFAULT_PROPERTIES += security.perf_harden=1
 
   ifeq ($(user_variant),user)
     ADDITIONAL_DEFAULT_PROPERTIES += ro.adb.secure=1