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author kent <kent@cr.ie.u-ryukyu.ac.jp>
date Fri, 17 Jul 2009 14:47:48 +0900
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1 /* Linux host-specific hook definitions.
2 Copyright (C) 2004, 2005, 2007, 2008 Free Software Foundation, Inc.
3
4 This file is part of GCC.
5
6 GCC is free software; you can redistribute it and/or modify it
7 under the terms of the GNU General Public License as published
8 by the Free Software Foundation; either version 3, or (at your
9 option) any later version.
10
11 GCC is distributed in the hope that it will be useful, but WITHOUT
12 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
13 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
14 License for more details.
15
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
19
20 #include "config.h"
21 #include "system.h"
22 #include "coretypes.h"
23 #include <sys/mman.h>
24 #include <limits.h>
25 #include "hosthooks.h"
26 #include "hosthooks-def.h"
27
28
29 /* Linux has a feature called exec-shield-randomize that perturbs the
30 address of non-fixed mapped segments by a (relatively) small amount.
31 The feature is intended to make it harder to attack the system with
32 buffer overflow attacks, since every invocation of a program will
33 have its libraries and data segments at slightly different addresses.
34
35 This feature causes us problems with PCH because it makes it that
36 much harder to acquire a stable location at which to map our PCH
37 data file.
38
39 [ The feature causes other points of non-determinism within the
40 compiler as well, so we'd *really* like to be able to have the
41 driver disable exec-shield-randomize for the process group, but
42 that isn't possible at present. ]
43
44 We're going to try several things:
45
46 * Select an architecture specific address as "likely" and see
47 if that's free. For our 64-bit hosts, we can easily choose
48 an address in Never Never Land.
49
50 * If exec-shield-randomize is disabled, then just use the
51 address chosen by mmap in step one.
52
53 * If exec-shield-randomize is enabled, then temporarily allocate
54 32M of memory as a buffer, then allocate PCH memory, then
55 free the buffer. The theory here is that the perturbation is
56 no more than 16M, and so by allocating our buffer larger than
57 that we make it considerably more likely that the address will
58 be free when we want to load the data back.
59 */
60
61 #undef HOST_HOOKS_GT_PCH_GET_ADDRESS
62 #define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address
63
64 #undef HOST_HOOKS_GT_PCH_USE_ADDRESS
65 #define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address
66
67 /* For various ports, try to guess a fixed spot in the vm space
68 that's probably free. */
69 #if defined(__alpha)
70 # define TRY_EMPTY_VM_SPACE 0x10000000000
71 #elif defined(__ia64)
72 # define TRY_EMPTY_VM_SPACE 0x2000000100000000
73 #elif defined(__x86_64)
74 # define TRY_EMPTY_VM_SPACE 0x1000000000
75 #elif defined(__i386)
76 # define TRY_EMPTY_VM_SPACE 0x60000000
77 #elif defined(__powerpc__)
78 # define TRY_EMPTY_VM_SPACE 0x60000000
79 #elif defined(__s390x__)
80 # define TRY_EMPTY_VM_SPACE 0x8000000000
81 #elif defined(__s390__)
82 # define TRY_EMPTY_VM_SPACE 0x60000000
83 #elif defined(__sparc__) && defined(__LP64__)
84 # define TRY_EMPTY_VM_SPACE 0x8000000000
85 #elif defined(__sparc__)
86 # define TRY_EMPTY_VM_SPACE 0x60000000
87 #elif defined(__mc68000__)
88 # define TRY_EMPTY_VM_SPACE 0x40000000
89 #else
90 # define TRY_EMPTY_VM_SPACE 0
91 #endif
92
93 /* Determine a location where we might be able to reliably allocate SIZE
94 bytes. FD is the PCH file, though we should return with the file
95 unmapped. */
96
97 static void *
98 linux_gt_pch_get_address (size_t size, int fd)
99 {
100 size_t buffer_size = 32 * 1024 * 1024;
101 void *addr, *buffer;
102 FILE *f;
103 bool randomize_on;
104
105 addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
106 MAP_PRIVATE, fd, 0);
107
108 /* If we failed the map, that means there's *no* free space. */
109 if (addr == (void *) MAP_FAILED)
110 return NULL;
111 /* Unmap the area before returning. */
112 munmap (addr, size);
113
114 /* If we got the exact area we requested, then that's great. */
115 if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
116 return addr;
117
118 /* If we didn't, then we need to look to see if virtual address
119 randomization is on. That is recorded in
120 kernel.randomize_va_space. An older implementation used
121 kernel.exec-shield-randomize. */
122 f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
123 if (f == NULL)
124 f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
125 randomize_on = false;
126 if (f != NULL)
127 {
128 char buf[100];
129 size_t c;
130
131 c = fread (buf, 1, sizeof buf - 1, f);
132 if (c > 0)
133 {
134 buf[c] = '\0';
135 randomize_on = (atoi (buf) > 0);
136 }
137 fclose (f);
138 }
139
140 /* If it isn't, then accept the address that mmap selected as fine. */
141 if (!randomize_on)
142 return addr;
143
144 /* Otherwise, we need to try again with buffer space. */
145 buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
146 addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
147 if (buffer != (void *) MAP_FAILED)
148 munmap (buffer, buffer_size);
149 if (addr == (void *) MAP_FAILED)
150 return NULL;
151 munmap (addr, size);
152
153 return addr;
154 }
155
156 /* Map SIZE bytes of FD+OFFSET at BASE. Return 1 if we succeeded at
157 mapping the data at BASE, -1 if we couldn't.
158
159 It's not possibly to reliably mmap a file using MAP_PRIVATE to
160 a specific START address on either hpux or linux. First we see
161 if mmap with MAP_PRIVATE works. If it does, we are off to the
162 races. If it doesn't, we try an anonymous private mmap since the
163 kernel is more likely to honor the BASE address in anonymous maps.
164 We then copy the data to the anonymous private map. This assumes
165 of course that we don't need to change the data in the PCH file
166 after it is created.
167
168 This approach obviously causes a performance penalty but there is
169 little else we can do given the current PCH implementation. */
170
171 static int
172 linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
173 {
174 void *addr;
175
176 /* We're called with size == 0 if we're not planning to load a PCH
177 file at all. This allows the hook to free any static space that
178 we might have allocated at link time. */
179 if (size == 0)
180 return -1;
181
182 /* Try to map the file with MAP_PRIVATE. */
183 addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
184
185 if (addr == base)
186 return 1;
187
188 if (addr != (void *) MAP_FAILED)
189 munmap (addr, size);
190
191 /* Try to make an anonymous private mmap at the desired location. */
192 addr = mmap (base, size, PROT_READ | PROT_WRITE,
193 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
194
195 if (addr != base)
196 {
197 if (addr != (void *) MAP_FAILED)
198 munmap (addr, size);
199 return -1;
200 }
201
202 if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
203 return -1;
204
205 while (size)
206 {
207 ssize_t nbytes;
208
209 nbytes = read (fd, base, MIN (size, SSIZE_MAX));
210 if (nbytes <= 0)
211 return -1;
212 base = (char *) base + nbytes;
213 size -= nbytes;
214 }
215
216 return 1;
217 }
218
219
220 const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;