1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
|
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/*
* A poison value that can be used to fill a memory space with
* an address that leads to a safe crash when dereferenced.
*/
#include "mozilla/Poison.h"
#include "mozilla/Assertions.h"
#ifdef _WIN32
# include <windows.h>
#elif !defined(__OS2__)
# include <unistd.h>
# ifndef __wasi__
# include <sys/mman.h>
# ifndef MAP_ANON
# ifdef MAP_ANONYMOUS
# define MAP_ANON MAP_ANONYMOUS
# else
# error "Don't know how to get anonymous memory"
# endif
# endif
# endif
#endif
// Freed memory is filled with a poison value, which we arrange to
// form a pointer either to an always-unmapped region of the address
// space, or to a page that has been reserved and rendered
// inaccessible via OS primitives. See tests/TestPoisonArea.cpp for
// extensive discussion of the requirements for this page. The code
// from here to 'class FreeList' needs to be kept in sync with that
// file.
#ifdef _WIN32
static void* ReserveRegion(uintptr_t aRegion, uintptr_t aSize) {
return VirtualAlloc((void*)aRegion, aSize, MEM_RESERVE, PAGE_NOACCESS);
}
static void ReleaseRegion(void* aRegion, uintptr_t aSize) {
VirtualFree(aRegion, aSize, MEM_RELEASE);
}
static bool ProbeRegion(uintptr_t aRegion, uintptr_t aSize) {
SYSTEM_INFO sinfo;
GetSystemInfo(&sinfo);
if (aRegion >= (uintptr_t)sinfo.lpMaximumApplicationAddress &&
aRegion + aSize >= (uintptr_t)sinfo.lpMaximumApplicationAddress) {
return true;
} else {
return false;
}
}
static uintptr_t GetDesiredRegionSize() {
SYSTEM_INFO sinfo;
GetSystemInfo(&sinfo);
return sinfo.dwAllocationGranularity;
}
# define RESERVE_FAILED 0
#elif defined(__OS2__)
static void* ReserveRegion(uintptr_t aRegion, uintptr_t aSize) {
// OS/2 doesn't support allocation at an arbitrary address,
// so return an address that is known to be invalid.
return (void*)0xFFFD0000;
}
static void ReleaseRegion(void* aRegion, uintptr_t aSize) { return; }
static bool ProbeRegion(uintptr_t aRegion, uintptr_t aSize) {
// There's no reliable way to probe an address in the system
// arena other than by touching it and seeing if a trap occurs.
return false;
}
static uintptr_t GetDesiredRegionSize() {
// Page size is fixed at 4k.
return 0x1000;
}
# define RESERVE_FAILED 0
#elif defined(__wasi__)
# define RESERVE_FAILED 0
static void* ReserveRegion(uintptr_t aRegion, uintptr_t aSize) {
return RESERVE_FAILED;
}
static void ReleaseRegion(void* aRegion, uintptr_t aSize) { return; }
static bool ProbeRegion(uintptr_t aRegion, uintptr_t aSize) {
const auto pageSize = 1 << 16;
MOZ_ASSERT(pageSize == sysconf(_SC_PAGESIZE));
auto heapSize = __builtin_wasm_memory_size(0) * pageSize;
return aRegion + aSize < heapSize;
}
static uintptr_t GetDesiredRegionSize() { return 0; }
#else // __wasi__
# include "mozilla/TaggedAnonymousMemory.h"
static void* ReserveRegion(uintptr_t aRegion, uintptr_t aSize) {
return MozTaggedAnonymousMmap(reinterpret_cast<void*>(aRegion), aSize,
PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0,
"poison");
}
static void ReleaseRegion(void* aRegion, uintptr_t aSize) {
munmap(aRegion, aSize);
}
static bool ProbeRegion(uintptr_t aRegion, uintptr_t aSize) {
# ifdef XP_SOLARIS
if (posix_madvise(reinterpret_cast<void*>(aRegion), aSize,
POSIX_MADV_NORMAL)) {
# else
if (madvise(reinterpret_cast<void*>(aRegion), aSize, MADV_NORMAL)) {
# endif
return true;
}
return false;
}
static uintptr_t GetDesiredRegionSize() { return sysconf(_SC_PAGESIZE); }
# define RESERVE_FAILED MAP_FAILED
#endif // system dependencies
static_assert((sizeof(uintptr_t) == 4 || sizeof(uintptr_t) == 8) &&
(sizeof(uintptr_t) == sizeof(void*)));
static uintptr_t ReservePoisonArea(uintptr_t rgnsize) {
if (sizeof(uintptr_t) == 8) {
// Use the hardware-inaccessible region.
// We have to avoid 64-bit constants and shifts by 32 bits, since this
// code is compiled in 32-bit mode, although it is never executed there.
return (((uintptr_t(0x7FFFFFFFu) << 31) << 1 | uintptr_t(0xF0DEAFFFu)) &
~(rgnsize - 1));
}
// First see if we can allocate the preferred poison address from the OS.
uintptr_t candidate = (0xF0DEAFFF & ~(rgnsize - 1));
void* result = ReserveRegion(candidate, rgnsize);
if (result == (void*)candidate) {
// success - inaccessible page allocated
return candidate;
}
// That didn't work, so see if the preferred address is within a range
// of permanently inacessible memory.
if (ProbeRegion(candidate, rgnsize)) {
// success - selected page cannot be usable memory
if (result != RESERVE_FAILED) {
ReleaseRegion(result, rgnsize);
}
return candidate;
}
// The preferred address is already in use. Did the OS give us a
// consolation prize?
if (result != RESERVE_FAILED) {
return uintptr_t(result);
}
// It didn't, so try to allocate again, without any constraint on
// the address.
result = ReserveRegion(0, rgnsize);
if (result != RESERVE_FAILED) {
return uintptr_t(result);
}
MOZ_CRASH("no usable poison region identified");
}
static uintptr_t GetPoisonValue(uintptr_t aBase, uintptr_t aSize) {
if (aSize == 0) { // can't happen
return 0;
}
return aBase + aSize / 2 - 1;
}
// Poison is used so pervasively throughout the codebase that we decided it was
// best to actually use ordered dynamic initialization of globals (AKA static
// constructors) for this. This way everything will have properly initialized
// poison -- except other dynamic initialization code in libmozglue, which there
// shouldn't be much of. (libmozglue is one of the first things loaded, and
// specifically comes before libxul, so nearly all gecko code runs strictly
// after this.)
extern "C" {
uintptr_t gMozillaPoisonSize = GetDesiredRegionSize();
uintptr_t gMozillaPoisonBase = ReservePoisonArea(gMozillaPoisonSize);
uintptr_t gMozillaPoisonValue =
GetPoisonValue(gMozillaPoisonBase, gMozillaPoisonSize);
}
|
