1 // Copyright 2014 The Chromium Authors
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #include "partition_alloc/address_space_randomization.h"
6 
7 #include "build/build_config.h"
8 #include "partition_alloc/partition_alloc_buildflags.h"
9 #include "partition_alloc/partition_alloc_check.h"
10 #include "partition_alloc/random.h"
11 
12 #if BUILDFLAG(IS_WIN)
13 #include <windows.h>
14 #endif
15 
16 namespace partition_alloc {
17 
GetRandomPageBase()18 uintptr_t GetRandomPageBase() {
19   uintptr_t random = static_cast<uintptr_t>(internal::RandomValue());
20 
21 #if BUILDFLAG(HAS_64_BIT_POINTERS)
22   random <<= 32ULL;
23   random |= static_cast<uintptr_t>(internal::RandomValue());
24 
25   // The ASLRMask() and ASLROffset() constants will be suitable for the
26   // OS and build configuration.
27   random &= internal::ASLRMask();
28   random += internal::ASLROffset();
29 #else  // BUILDFLAG(HAS_64_BIT_POINTERS)
30 #if BUILDFLAG(IS_WIN)
31   // On win32 host systems the randomization plus huge alignment causes
32   // excessive fragmentation. Plus most of these systems lack ASLR, so the
33   // randomization isn't buying anything. In that case we just skip it.
34   // TODO(palmer): Just dump the randomization when HE-ASLR is present.
35   static BOOL is_wow64 = -1;
36   if (is_wow64 == -1 && !IsWow64Process(GetCurrentProcess(), &is_wow64)) {
37     is_wow64 = FALSE;
38   }
39   if (!is_wow64) {
40     return 0;
41   }
42 #endif  // BUILDFLAG(IS_WIN)
43   random &= internal::ASLRMask();
44   random += internal::ASLROffset();
45 #endif  // BUILDFLAG(HAS_64_BIT_POINTERS)
46 
47   PA_DCHECK(!(random & internal::PageAllocationGranularityOffsetMask()));
48   return random;
49 }
50 
51 }  // namespace partition_alloc
52