Write protect executable pages in the VM.

runtime/vm/virtual_memory_win.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/globals.h"
 #if defined(TARGET_OS_WINDOWS)
 
 #include "vm/virtual_memory.h"
 
 #include "platform/assert.h"
@@ skipping 45 matching lines @@
   ASSERT(Contains(addr));
   ASSERT(Contains(addr + size) || (addr + size == end()));
   int prot = executable ? PAGE_EXECUTE_READWRITE : PAGE_READWRITE;
   if (VirtualAlloc(address(), size, MEM_COMMIT, prot) == NULL) {
     return false;
   }
   return true;
 }
 
 
-bool VirtualMemory::Protect(Protection mode) {
+bool VirtualMemory::Protect(void* address, intptr_t size, Protection mode) {
+  uword start_address = reinterpret_cast<uword>(address);
+  uword end_address = start_address + size;
+  uword page_address = start_address & ~(PageSize() - 1);
   DWORD prot = 0;
   switch (mode) {
     case kNoAccess:
       prot = PAGE_NOACCESS;
       break;
     case kReadOnly:
       prot = PAGE_READONLY;
       break;
     case kReadWrite:
       prot = PAGE_READWRITE;
       break;
     case kReadExecute:
       prot = PAGE_EXECUTE_READ;
       break;
     case kReadWriteExecute:
       prot = PAGE_EXECUTE_READWRITE;
       break;
   }
   DWORD old_prot = 0;
-  return VirtualProtect(address(), size(), prot, &old_prot);
+  return VirtualProtect(reinterpret_cast<void*>(address),
+                        end_address - page_address,
+                        prot,
+                        &old_prot);
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_WINDOWS)