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1 : : /* Linux host-specific hook definitions.
2 : : Copyright (C) 2004-2024 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 : : #elif defined(__riscv) && defined (__LP64__)
100 : : # define TRY_EMPTY_VM_SPACE 0x1000000000
101 : : #elif defined(__loongarch__) && defined(__LP64__)
102 : : # define TRY_EMPTY_VM_SPACE 0x1000000000
103 : : #else
104 : : # define TRY_EMPTY_VM_SPACE 0
105 : : #endif
106 : :
107 : : /* Determine a location where we might be able to reliably allocate SIZE
108 : : bytes. FD is the PCH file, though we should return with the file
109 : : unmapped. */
110 : :
111 : : static void *
112 : 478 : linux_gt_pch_get_address (size_t size, int fd)
113 : : {
114 : 478 : size_t buffer_size = 32 * 1024 * 1024;
115 : 478 : void *addr, *buffer;
116 : 478 : FILE *f;
117 : 478 : bool randomize_on;
118 : :
119 : 478 : addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
120 : : MAP_PRIVATE, fd, 0);
121 : :
122 : : /* If we failed the map, that means there's *no* free space. */
123 : 478 : if (addr == (void *) MAP_FAILED)
124 : : return NULL;
125 : : /* Unmap the area before returning. */
126 : 478 : munmap (addr, size);
127 : :
128 : : /* If we got the exact area we requested, then that's great. */
129 : 478 : if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
130 : : return addr;
131 : :
132 : : /* If we didn't, then we need to look to see if virtual address
133 : : randomization is on. That is recorded in
134 : : kernel.randomize_va_space. An older implementation used
135 : : kernel.exec-shield-randomize. */
136 : 0 : f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
137 : 0 : if (f == NULL)
138 : 0 : f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
139 : 0 : randomize_on = false;
140 : 0 : if (f != NULL)
141 : : {
142 : 0 : char buf[100];
143 : 0 : size_t c;
144 : :
145 : 0 : c = fread (buf, 1, sizeof buf - 1, f);
146 : 0 : if (c > 0)
147 : : {
148 : 0 : buf[c] = '\0';
149 : 0 : randomize_on = (atoi (buf) > 0);
150 : : }
151 : 0 : fclose (f);
152 : : }
153 : :
154 : : /* If it isn't, then accept the address that mmap selected as fine. */
155 : 0 : if (!randomize_on)
156 : 0 : return addr;
157 : :
158 : : /* Otherwise, we need to try again with buffer space. */
159 : 0 : buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
160 : 0 : addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
161 : 0 : if (buffer != (void *) MAP_FAILED)
162 : 0 : munmap (buffer, buffer_size);
163 : 0 : if (addr == (void *) MAP_FAILED)
164 : : return NULL;
165 : 0 : munmap (addr, size);
166 : :
167 : 0 : return addr;
168 : : }
169 : :
170 : : /* Map SIZE bytes of FD+OFFSET at BASE. Return 1 if we succeeded at
171 : : mapping the data at BASE, -1 if we couldn't.
172 : :
173 : : It's not possibly to reliably mmap a file using MAP_PRIVATE to
174 : : a specific START address on either hpux or linux. First we see
175 : : if mmap with MAP_PRIVATE works. If it does, we are off to the
176 : : races. If it doesn't, we try an anonymous private mmap since the
177 : : kernel is more likely to honor the BASE address in anonymous maps.
178 : : We then copy the data to the anonymous private map. This assumes
179 : : of course that we don't need to change the data in the PCH file
180 : : after it is created.
181 : :
182 : : This approach obviously causes a performance penalty but there is
183 : : little else we can do given the current PCH implementation. */
184 : :
185 : : static int
186 : 197251 : linux_gt_pch_use_address (void *&base, size_t size, int fd, size_t offset)
187 : : {
188 : 197251 : void *addr;
189 : :
190 : : /* We're called with size == 0 if we're not planning to load a PCH
191 : : file at all. This allows the hook to free any static space that
192 : : we might have allocated at link time. */
193 : 197251 : if (size == 0)
194 : : return -1;
195 : :
196 : : /* Try to map the file with MAP_PRIVATE. */
197 : 347 : addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
198 : :
199 : 347 : if (addr == base)
200 : : return 1;
201 : :
202 : 0 : if (addr != (void *) MAP_FAILED)
203 : 0 : munmap (addr, size);
204 : :
205 : : /* Try to make an anonymous private mmap at the desired location. */
206 : 0 : addr = mmap (base, size, PROT_READ | PROT_WRITE,
207 : : MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
208 : :
209 : 0 : if (addr == (void *) MAP_FAILED)
210 : : return -1;
211 : :
212 : 0 : if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
213 : : return -1;
214 : :
215 : 0 : base = addr;
216 : :
217 : 0 : while (size)
218 : : {
219 : 0 : ssize_t nbytes;
220 : :
221 : 0 : nbytes = read (fd, addr, MIN (size, (size_t)-1 >> 1));
222 : 0 : if (nbytes <= 0)
223 : : return -1;
224 : 0 : addr = (char *) addr + nbytes;
225 : 0 : size -= nbytes;
226 : : }
227 : :
228 : : return 1;
229 : : }
230 : :
231 : :
232 : : const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;
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