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1 : /* Linux host-specific hook definitions.
2 : Copyright (C) 2004-2026 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 *
112 428 : linux_gt_pch_get_address (size_t size, int fd)
113 : {
114 428 : size_t buffer_size = 32 * 1024 * 1024;
115 428 : void *addr, *buffer;
116 428 : FILE *f;
117 428 : bool randomize_on;
118 :
119 428 : 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. */
123 428 : if (addr == (void *) MAP_FAILED)
124 : return NULL;
125 : /* Unmap the area before returning. */
126 428 : munmap (addr, size);
127 :
128 : /* If we got the exact area we requested, then that's great. */
129 428 : 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 201319 : linux_gt_pch_use_address (void *&base, size_t size, int fd, size_t offset)
187 : {
188 201319 : 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 201319 : if (size == 0)
194 : return -1;
195 :
196 : /* Try to map the file with MAP_PRIVATE. */
197 350 : addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
198 :
199 350 : 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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