Randomize allocation addresses on windows.

src/platform-win32.cc

Index: src/platform-win32.cc
===================================================================
--- src/platform-win32.cc	(revision 10785)
+++ src/platform-win32.cc	(working copy)
@@ -830,10 +830,7 @@
   return allocate_alignment;
 }
 

[Vyacheslav Egorov (Chromium), 2012/02/22 12:22:36]

one more new line

-
-void* OS::Allocate(const size_t requested,
-                   size_t* allocated,
-                   bool is_executable) {
+void* OS::GetRandomAddr() {
   // The address range used to randomize RWX allocations in OS::Allocate
   // Try not to map pages into the default range that windows loads DLLs
   // Use a multiple of 64k to prevent committing unused memory.
@@ -846,10 +843,18 @@
   static const intptr_t kAllocationRandomAddressMin = 0x04000000;
   static const intptr_t kAllocationRandomAddressMax = 0x3FFF0000;
 #endif
+  uintptr_t address = (V8::RandomPrivate(Isolate::Current()) << kPageSizeBits)
+      | kAllocationRandomAddressMin;
+  address &= kAllocationRandomAddressMax;
+  return reinterpret_cast<void *>(address);
+}
 

[Vyacheslav Egorov (Chromium), 2012/02/22 12:22:36]

one more new line

+void* OS::Allocate(const size_t requested,
+                   size_t* allocated,
+                   bool is_executable) {
   // VirtualAlloc rounds allocated size to page size automatically.
   size_t msize = RoundUp(requested, static_cast<int>(GetPageSize()));
-  intptr_t address = 0;
+  void* address = 0;
 
   // Windows XP SP2 allows Data Excution Prevention (DEP).
   int prot = is_executable ? PAGE_EXECUTE_READWRITE : PAGE_READWRITE;
@@ -857,12 +862,10 @@
   // For exectutable pages try and randomize the allocation address
   if (prot == PAGE_EXECUTE_READWRITE &&
       msize >= static_cast<size_t>(Page::kPageSize)) {
-    address = (V8::RandomPrivate(Isolate::Current()) << kPageSizeBits)
-      | kAllocationRandomAddressMin;
-    address &= kAllocationRandomAddressMax;
+    address = OS::GetRandomAddr();

[Vyacheslav Egorov (Chromium), 2012/02/22 12:22:36]

I don't think GetRandomAddr has to be member of OS it could as well be just a
static global function.

   }
 
-  LPVOID mbase = VirtualAlloc(reinterpret_cast<void *>(address),
+  LPVOID mbase = VirtualAlloc(address,
                               msize,
                               MEM_COMMIT | MEM_RESERVE,
                               prot);
@@ -1471,7 +1474,18 @@
 
 
 void* VirtualMemory::ReserveRegion(size_t size) {
-  return VirtualAlloc(NULL, size, MEM_RESERVE, PAGE_NOACCESS);
+  void* address = 0;
+  LPVOID mbase = NULL;
+
+  for (size_t attempts = 0; mbase == NULL && attempts < 3; ++attempts) {
+    address = OS::GetRandomAddr();
+    mbase = VirtualAlloc(address, size, MEM_RESERVE, PAGE_NOACCESS);
+  }
+
+  // After three attempts give up and let the OS find an address to use.
+  if (mbase == NULL)
+    mbase = VirtualAlloc(NULL, size, MEM_RESERVE, PAGE_NOACCESS);

[Vyacheslav Egorov (Chromium), 2012/02/22 12:22:36]

we do not omit {} for if-s that span several lines.

+  return mbase;

[Vyacheslav Egorov (Chromium), 2012/02/22 12:22:36]

I would abstract loop and last attempt into a function and call it from two
different places. 

 }