1 /* Linux host-specific hook definitions.
2 Copyright (C) 2004-2018 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 "hosthooks.h"
24 #include "hosthooks-def.h"
25
26
27 /* Linux has a feature called exec-shield-randomize that perturbs the
28 address of non-fixed mapped segments by a (relatively) small amount.
29 The feature is intended to make it harder to attack the system with
30 buffer overflow attacks, since every invocation of a program will
31 have its libraries and data segments at slightly different addresses.
32
33 This feature causes us problems with PCH because it makes it that
34 much harder to acquire a stable location at which to map our PCH
35 data file.
36
37 [ The feature causes other points of non-determinism within the
38 compiler as well, so we'd *really* like to be able to have the
39 driver disable exec-shield-randomize for the process group, but
40 that isn't possible at present. ]
41
42 We're going to try several things:
43
44 * Select an architecture specific address as "likely" and see
45 if that's free. For our 64-bit hosts, we can easily choose
46 an address in Never Never Land.
47
48 * If exec-shield-randomize is disabled, then just use the
49 address chosen by mmap in step one.
50
51 * If exec-shield-randomize is enabled, then temporarily allocate
52 32M of memory as a buffer, then allocate PCH memory, then
53 free the buffer. The theory here is that the perturbation is
54 no more than 16M, and so by allocating our buffer larger than
55 that we make it considerably more likely that the address will
56 be free when we want to load the data back.
57 */
58
59 #undef HOST_HOOKS_GT_PCH_GET_ADDRESS
60 #define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address
61
62 #undef HOST_HOOKS_GT_PCH_USE_ADDRESS
63 #define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address
64
65 /* For various ports, try to guess a fixed spot in the vm space
66 that's probably free. */
67 #if defined(__alpha)
68 # define TRY_EMPTY_VM_SPACE 0x10000000000
69 #elif defined(__ia64)
70 # define TRY_EMPTY_VM_SPACE 0x2000000100000000
71 #elif defined(__x86_64) && defined(__LP64__)
72 # define TRY_EMPTY_VM_SPACE 0x1000000000
73 #elif defined(__x86_64)
74 # define TRY_EMPTY_VM_SPACE 0x60000000
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 #elif defined(__aarch64__) && defined(__ILP32__)
90 # define TRY_EMPTY_VM_SPACE 0x60000000
91 #elif defined(__aarch64__)
92 # define TRY_EMPTY_VM_SPACE 0x1000000000
93 #elif defined(__ARM_EABI__)
94 # define TRY_EMPTY_VM_SPACE 0x60000000
95 #elif defined(__mips__) && defined(__LP64__)
96 # define TRY_EMPTY_VM_SPACE 0x8000000000
97 #elif defined(__mips__)
98 # define TRY_EMPTY_VM_SPACE 0x60000000
99 #else
100 # define TRY_EMPTY_VM_SPACE 0
101 #endif
102
103 /* Determine a location where we might be able to reliably allocate SIZE
104 bytes. FD is the PCH file, though we should return with the file
105 unmapped. */
106
107 static void *
linux_gt_pch_get_address(size_t size,int fd)108 linux_gt_pch_get_address (size_t size, int fd)
109 {
110 size_t buffer_size = 32 * 1024 * 1024;
111 void *addr, *buffer;
112 FILE *f;
113 bool randomize_on;
114
115 addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
116 MAP_PRIVATE, fd, 0);
117
118 /* If we failed the map, that means there's *no* free space. */
119 if (addr == (void *) MAP_FAILED)
120 return NULL;
121 /* Unmap the area before returning. */
122 munmap (addr, size);
123
124 /* If we got the exact area we requested, then that's great. */
125 if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
126 return addr;
127
128 /* If we didn't, then we need to look to see if virtual address
129 randomization is on. That is recorded in
130 kernel.randomize_va_space. An older implementation used
131 kernel.exec-shield-randomize. */
132 f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
133 if (f == NULL)
134 f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
135 randomize_on = false;
136 if (f != NULL)
137 {
138 char buf[100];
139 size_t c;
140
141 c = fread (buf, 1, sizeof buf - 1, f);
142 if (c > 0)
143 {
144 buf[c] = '\0';
145 randomize_on = (atoi (buf) > 0);
146 }
147 fclose (f);
148 }
149
150 /* If it isn't, then accept the address that mmap selected as fine. */
151 if (!randomize_on)
152 return addr;
153
154 /* Otherwise, we need to try again with buffer space. */
155 buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
156 addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
157 if (buffer != (void *) MAP_FAILED)
158 munmap (buffer, buffer_size);
159 if (addr == (void *) MAP_FAILED)
160 return NULL;
161 munmap (addr, size);
162
163 return addr;
164 }
165
166 /* Map SIZE bytes of FD+OFFSET at BASE. Return 1 if we succeeded at
167 mapping the data at BASE, -1 if we couldn't.
168
169 It's not possibly to reliably mmap a file using MAP_PRIVATE to
170 a specific START address on either hpux or linux. First we see
171 if mmap with MAP_PRIVATE works. If it does, we are off to the
172 races. If it doesn't, we try an anonymous private mmap since the
173 kernel is more likely to honor the BASE address in anonymous maps.
174 We then copy the data to the anonymous private map. This assumes
175 of course that we don't need to change the data in the PCH file
176 after it is created.
177
178 This approach obviously causes a performance penalty but there is
179 little else we can do given the current PCH implementation. */
180
181 static int
linux_gt_pch_use_address(void * base,size_t size,int fd,size_t offset)182 linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
183 {
184 void *addr;
185
186 /* We're called with size == 0 if we're not planning to load a PCH
187 file at all. This allows the hook to free any static space that
188 we might have allocated at link time. */
189 if (size == 0)
190 return -1;
191
192 /* Try to map the file with MAP_PRIVATE. */
193 addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
194
195 if (addr == base)
196 return 1;
197
198 if (addr != (void *) MAP_FAILED)
199 munmap (addr, size);
200
201 /* Try to make an anonymous private mmap at the desired location. */
202 addr = mmap (base, size, PROT_READ | PROT_WRITE,
203 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
204
205 if (addr != base)
206 {
207 if (addr != (void *) MAP_FAILED)
208 munmap (addr, size);
209 return -1;
210 }
211
212 if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
213 return -1;
214
215 while (size)
216 {
217 ssize_t nbytes;
218
219 nbytes = read (fd, base, MIN (size, (size_t)-1 >> 1));
220 if (nbytes <= 0)
221 return -1;
222 base = (char *) base + nbytes;
223 size -= nbytes;
224 }
225
226 return 1;
227 }
228
229
230 const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;
231