Use the full 47 bits of address space on Windows >= 8.1.

base/allocator/partition_allocator/address_space_randomization.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/allocator/partition_allocator/address_space_randomization.h"
 
 #include "base/allocator/partition_allocator/page_allocator.h"
 #include "base/allocator/partition_allocator/spin_lock.h"
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
+#include <VersionHelpers.h>
 #else
 #include <sys/time.h>
 #include <unistd.h>
 #endif
 
 namespace base {
 
 namespace {
 
 // This is the same PRNG as used by tcmalloc for mapping address randomness;
@@ skipping 59 matching lines @@
 // balance good ASLR against not fragmenting the address space too badly.
 void* GetRandomPageBase() {
   uintptr_t random;
   random = static_cast<uintptr_t>(ranval(&s_ranctx));
 #if defined(ARCH_CPU_X86_64)
   random <<= 32UL;
   random |= static_cast<uintptr_t>(ranval(&s_ranctx));
 // This address mask gives a low likelihood of address space collisions. We
 // handle the situation gracefully if there is a collision.
 #if defined(OS_WIN)
-  // 64-bit Windows has a bizarrely small 8TB user address space. Allocates in
-  // the 1-5TB region. TODO(palmer): See if Windows >= 8.1 has the full 47 bits,
-  // and use it if so. crbug.com/672219
   random &= 0x3ffffffffffUL;
-  random += 0x10000000000UL;
+  // Windows >= 8.1 has the full 47 bits. Use them where available.
+  static bool windows_81 = false;
+  static bool windows_81_initialized = false;
+  if (!windows_81_initialized) {
+    windows_81 = IsWindows8Point1OrGreater();

[Will Harris, 2017/03/28 16:42:16]

can this code use base::win::GetVersion - by convention we prefer to use these
base apis rather than the windows ones.

Also, it takes care of the lazy initialization.

[palmer, 2017/03/28 19:05:35]

Thanks. Using it now, although I might have to go back to
IsWindows8Point1OrGreater if we end up needing to further reduces PA's base
dependencies.

+    windows_81_initialized = true;
+  }
+  if (!windows_81) {
+    random += 0x10000000000UL;
+  }
 #elif defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
   // This range is copied from the TSan source, but works for all tools.
   random &= 0x007fffffffffUL;
   random += 0x7e8000000000UL;
 #else
   // Linux and OS X support the full 47-bit user space of x64 processors.
   random &= 0x3fffffffffffUL;
 #endif
 #elif defined(ARCH_CPU_ARM64)
   // ARM64 on Linux has 39-bit user space.
@@ skipping 14 matching lines @@
   // This is a good range on Windows, Linux and Mac.
   // Allocates in the 0.5-1.5GB region.
   random &= 0x3fffffff;
   random += 0x20000000;
 #endif  // defined(ARCH_CPU_X86_64)
   random &= kPageAllocationGranularityBaseMask;
   return reinterpret_cast<void*>(random);
 }
 
 }  // namespace base