Stop initializing code pages with RWX permissions

runtime/vm/pages.cc

Index: runtime/vm/pages.cc
diff --git a/runtime/vm/pages.cc b/runtime/vm/pages.cc
index 5d5df0e2d559398f7494b34059206646c3399233..02a566c1a256faf33b4333ca78a8ed27bc6b3975 100644
--- a/runtime/vm/pages.cc
+++ b/runtime/vm/pages.cc
@@ -50,7 +50,9 @@ HeapPage* HeapPage::Initialize(VirtualMemory* memory, PageType type) {
   ASSERT(memory != NULL);
   ASSERT(memory->size() > VirtualMemory::PageSize());
   bool is_executable = (type == kExecutable);
-  if (!memory->Commit(is_executable)) {
+  // Create the new page executable (RWX) only if we're not in W^X mode
+  bool create_executable = !FLAG_write_protect_code;

[siva, 2016/01/28 00:10:16]

Shouldn't this be

bool create_executable = !FLAG_write_protect_code && is_executable;

otherwise you end up creating executable pages even not asked for when the flag
is not set.

[Todd Eisenberger, 2016/01/28 00:21:05]

Good catch; got caught up with finding the RWX leak that I forgot about the non
protected case.

+  if (!memory->Commit(create_executable)) {
     return NULL;
   }
   HeapPage* result = reinterpret_cast<HeapPage*>(memory->address());