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Side by Side Diff: Source/wtf/AddressSpaceRandomization.cpp

Issue 343753004: Oilpan: Improve address space randomization for the Oilpan heap. (Closed) Base URL: svn://svn.chromium.org/blink/trunk
Patch Set: fix typo Created 6 years, 5 months ago
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1 // Copyright 2014 The Chromium Authors. All rights reserved.
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 "config.h"
6 #include "wtf/AddressSpaceRandomization.h"
7
8 #include "wtf/PageAllocator.h"
9 #include "wtf/ProcessID.h"
10 #include "wtf/SpinLock.h"
11
12 namespace WTF {
13
14 namespace {
15
16 // This is the same PRNG as used by tcmalloc for mapping address randomness;
17 // see http://burtleburtle.net/bob/rand/smallprng.html
18 struct ranctx {
19 int lock;
20 bool initialized;
21 uint32_t a;
22 uint32_t b;
23 uint32_t c;
24 uint32_t d;
25 };
26
27 #define rot(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
28
29 uint32_t ranvalInternal(ranctx* x)
30 {
31 uint32_t e = x->a - rot(x->b, 27);
32 x->a = x->b ^ rot(x->c, 17);
33 x->b = x->c + x->d;
34 x->c = x->d + e;
35 x->d = e + x->a;
36 return x->d;
37 }
38
39 #undef rot
40
41 uint32_t ranval(ranctx* x)
42 {
43 spinLockLock(&x->lock);
44 if (UNLIKELY(!x->initialized)) {
45 x->initialized = true;
46 char c;
47 uint32_t seed = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(&c));
48 seed ^= static_cast<uint32_t>(getCurrentProcessID());
49 x->a = 0xf1ea5eed;
50 x->b = x->c = x->d = seed;
51 for (int i = 0; i < 20; ++i) {
52 (void) ranvalInternal(x);
53 }
54 }
55 uint32_t ret = ranvalInternal(x);
56 spinLockUnlock(&x->lock);
57 return ret;
58 }
59
60 static struct ranctx s_ranctx;
61
62 }
63
64 // Calculates a random preferred mapping address. In calculating an
65 // address, we balance good ASLR against not fragmenting the address
66 // space too badly.
67 void* getRandomPageBase()
68 {
69 uintptr_t random;
70 random = static_cast<uintptr_t>(ranval(&s_ranctx));
71 #if CPU(X86_64)
72 random <<= 32UL;
73 random |= static_cast<uintptr_t>(ranval(&s_ranctx));
74 // This address mask gives a low liklihood of address space collisions.
75 // We handle the situation gracefully if there is a collision.
76 #if OS(WIN)
77 // 64-bit Windows has a bizarrely small 8TB user address space.
78 // Allocates in the 1-5TB region.
79 random &= 0x3ffffffffffUL;
80 random += 0x10000000000UL;
81 #else
82 // Linux and OS X support the full 47-bit user space of x64 processors.
83 random &= 0x3fffffffffffUL;
84 #endif
85 #elif CPU(ARM64)
86 // ARM64 on Linux has 39-bit user space.
87 random &= 0x3fffffffffUL;
88 random += 0x1000000000UL;
89 #else // !CPU(X86_64) && !CPU(ARM64)
90 // This is a good range on Windows, Linux and Mac.
91 // Allocates in the 0.5-1.5GB region.
92 random &= 0x3fffffff;
93 random += 0x20000000;
94 #endif // CPU(X86_64)
95 random &= kPageAllocationGranularityBaseMask;
96 return reinterpret_cast<void*>(random);
97 }
98
99 }
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