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53ee4dac | 1 | /* Linux host-specific hook definitions. |
f1717362 | 2 | Copyright (C) 2004-2016 Free Software Foundation, Inc. |
53ee4dac | 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 | |
038d1e19 | 8 | by the Free Software Foundation; either version 3, or (at your |
53ee4dac | 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 | |
038d1e19 | 17 | along with GCC; see the file COPYING3. If not see |
18 | <http://www.gnu.org/licenses/>. */ | |
53ee4dac | 19 | |
20 | #include "config.h" | |
21 | #include "system.h" | |
22 | #include "coretypes.h" | |
53ee4dac | 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 | ||
da7821f5 | 62 | #undef HOST_HOOKS_GT_PCH_USE_ADDRESS |
63 | #define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address | |
64 | ||
53ee4dac | 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 | |
7a1c6e92 | 71 | #elif defined(__x86_64) && defined(__LP64__) |
53ee4dac | 72 | # define TRY_EMPTY_VM_SPACE 0x1000000000 |
7a1c6e92 | 73 | #elif defined(__x86_64) |
74 | # define TRY_EMPTY_VM_SPACE 0x60000000 | |
53ee4dac | 75 | #elif defined(__i386) |
76 | # define TRY_EMPTY_VM_SPACE 0x60000000 | |
64e3aa3a | 77 | #elif defined(__powerpc__) |
78 | # define TRY_EMPTY_VM_SPACE 0x60000000 | |
91b6c440 | 79 | #elif defined(__s390x__) |
80 | # define TRY_EMPTY_VM_SPACE 0x8000000000 | |
81 | #elif defined(__s390__) | |
82 | # define TRY_EMPTY_VM_SPACE 0x60000000 | |
15b2ce92 | 83 | #elif defined(__sparc__) && defined(__LP64__) |
84 | # define TRY_EMPTY_VM_SPACE 0x8000000000 | |
85 | #elif defined(__sparc__) | |
86 | # define TRY_EMPTY_VM_SPACE 0x60000000 | |
19f42ddf | 87 | #elif defined(__mc68000__) |
88 | # define TRY_EMPTY_VM_SPACE 0x40000000 | |
e4b851a3 | 89 | #elif defined(__aarch64__) && defined(__ILP32__) |
90 | # define TRY_EMPTY_VM_SPACE 0x60000000 | |
f2139b9c | 91 | #elif defined(__aarch64__) |
92 | # define TRY_EMPTY_VM_SPACE 0x1000000000 | |
c275616e | 93 | #elif defined(__ARM_EABI__) |
94 | # define TRY_EMPTY_VM_SPACE 0x60000000 | |
d928709e | 95 | #elif defined(__mips__) && defined(__LP64__) |
96 | # define TRY_EMPTY_VM_SPACE 0x8000000000 | |
97 | #elif defined(__mips__) | |
98 | # define TRY_EMPTY_VM_SPACE 0x60000000 | |
53ee4dac | 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 * | |
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 | ||
5293fdcb | 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"); | |
53ee4dac | 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 | ||
da7821f5 | 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 | |
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 | ||
bfd54518 | 219 | nbytes = read (fd, base, MIN (size, (size_t)-1 >> 1)); |
da7821f5 | 220 | if (nbytes <= 0) |
221 | return -1; | |
222 | base = (char *) base + nbytes; | |
223 | size -= nbytes; | |
224 | } | |
225 | ||
226 | return 1; | |
227 | } | |
228 | ||
53ee4dac | 229 | \f |
230 | const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER; |