Add a guard page in front of metadata allocations.

third_party/tcmalloc/chromium/src/windows/port.cc

 /* Copyright (c) 2007, Google Inc.
  * All rights reserved.
  * 
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  * 
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 240 matching lines @@
   if (result == NULL)
     return NULL;
 
   // If the result is not aligned memory fragmentation will result which can
   // lead to pathological memory use.
   assert((reinterpret_cast<uintptr_t>(result) & (alignment - 1)) == 0);
 
   return result;
 }
 
+size_t TCMalloc_SystemAddGuard(void* start, size_t size) {
+  static size_t pagesize = 0;
+  if (pagesize == 0) {
+    SYSTEM_INFO system_info;
+    GetSystemInfo(&system_info);
+    pagesize = system_info.dwPageSize;
+  }
+

[jar (doing other things), 2011/11/24 00:30:54]

You need to exit if size < pagesize.

You might assert if you'd like.

[jschuh, 2011/11/24 01:02:05]

Ugh. That was dumb.

+  // We know that TCMalloc_SystemAlloc will give us a correct page alignment
+  // regardless, so we can just assert to detect erroneous callers.
+  assert(reinterpret_cast<size_t>(start) % pagesize == 0);
+
+  // Add a guard page to catch metadata corruption. We're using the
+  // PAGE_GUARD flag rather than NO_ACCESS because we want the unique
+  // exception in crash reports.
+  DWORD permissions = 0;
+  if (VirtualProtect(start, pagesize, PAGE_READONLY | PAGE_GUARD,
+                     &permissions)) {
+    return pagesize;
+  }
+
+  return 0;
+}
+
 void TCMalloc_SystemRelease(void* start, size_t length) {
   if (VirtualFree(start, length, MEM_DECOMMIT))
     return;
 
   // The decommit may fail if the memory region consists of allocations
   // from more than one call to VirtualAlloc.  In this case, fall back to
   // using VirtualQuery to retrieve the allocation boundaries and decommit
   // them each individually.
 
   char* ptr = static_cast<char*>(start);
@@ skipping 57 matching lines @@
       if ((strlen(fname) >= prefix_length) &&
           (memcmp(fname, prefix, prefix_length) == 0)) {
         RAW_VLOG(0, "Removing old heap profile %s\n", fname);
         // TODO(csilvers): we really need to unlink dirname + fname
         _unlink(fname);
       }
     } while (FindNextFileA(hFind, &found) != FALSE);  // A is for Ansi
     FindClose(hFind);
   }
 }