Make fastmalloc use guardpages

https://bugs.webkit.org/show_bug.cgi?id=111353

Reviewed by Anders Carlsson.

Add PROT_NONE pages at the beginning and end of every
mmap call made by fastmalloc.

* wtf/TCSystemAlloc.cpp:
(TryMmap):

Canonical link: https://commits.webkit.org/129984@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@144971 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WTF/ChangeLog

@@ -1,3 +1,16 @@
+2013-03-04  Oliver Hunt  <oliver@apple.com>
+
+        Make fastmalloc use guardpages
+        https://bugs.webkit.org/show_bug.cgi?id=111353
+
+        Reviewed by Anders Carlsson.
+
+        Add PROT_NONE pages at the beginning and end of every
+        mmap call made by fastmalloc.
+
+        * wtf/TCSystemAlloc.cpp:
+        (TryMmap):
+
 2013-03-06  Paweł Forysiuk  <tuxator@o2.pl>
 
         Typo in inline function in ByteOrder.h

Source/WTF/wtf/TCSystemAlloc.cpp

@@ -35,6 +35,7 @@
 #include "TCSystemAlloc.h"
 
 #include "Assertions.h"
+#include "CheckedArithmetic.h"
 #include "TCSpinLock.h"
 #include "UnusedParam.h"
 #include "VMTags.h"
@@ -166,15 +167,18 @@ static void* TryMmap(size_t size, size_t *actual_size, size_t alignment) {
   if (alignment > pagesize) {
     extra = alignment - pagesize;
   }
-  void* result = mmap(NULL, size + extra,
+  Checked<size_t> mapSize = Checked<size_t>(size) + extra + 2 * pagesize;
+  void* result = mmap(NULL, mapSize.unsafeGet(),
                       PROT_READ | PROT_WRITE,
                       MAP_PRIVATE|MAP_ANONYMOUS,
                       VM_TAG_FOR_TCMALLOC_MEMORY, 0);
   if (result == reinterpret_cast<void*>(MAP_FAILED)) {
     mmap_failure = true;
     return NULL;
   }
-
+  mmap(result, pagesize, PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANON, VM_TAG_FOR_TCMALLOC_MEMORY, 0);
+  mmap(static_cast<char*>(result) + (mapSize - pagesize).unsafeGet(), pagesize, PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANON, VM_TAG_FOR_TCMALLOC_MEMORY, 0);
+  result = static_cast<char*>(result) + pagesize;
   // Adjust the return memory so it is aligned
   uintptr_t ptr = reinterpret_cast<uintptr_t>(result);
   size_t adjust = 0;