Stop initializing code pages with RWX permissions

runtime/vm/pages.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/pages.h"
 
 #include "platform/assert.h"
 #include "vm/compiler_stats.h"
 #include "vm/gc_marker.h"
 #include "vm/gc_sweeper.h"
@@ skipping 32 matching lines @@
 #else  // TARGET_ARCH_MIPS || TARGET_ARCH_ARM64
 DEFINE_FLAG(bool, concurrent_sweep, true,
             "Concurrent sweep for old generation.");
 #endif  // TARGET_ARCH_MIPS || TARGET_ARCH_ARM64
 DEFINE_FLAG(bool, log_growth, false, "Log PageSpace growth policy decisions.");
 
 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());
   ASSERT(result != NULL);
   result->memory_ = memory;
   result->next_ = NULL;
   result->executable_ = is_executable;
   return result;
 }
 
@@ skipping 1151 matching lines @@
     return 0;
   } else {
     ASSERT(total_time >= gc_time);
     int result = static_cast<int>((static_cast<double>(gc_time) /
                                    static_cast<double>(total_time)) * 100);
     return result;
   }
 }
 
 }  // namespace dart