1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
|
/* SPDX-License-Identifier: LGPL-2.1+ */
/***
This file is part of systemd.
Copyright 2014 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <errno.h>
#include <signal.h>
#include <stddef.h>
#include <sys/mman.h>
#include "macro.h"
#include "sigbus.h"
#include "util.h"
#define SIGBUS_QUEUE_MAX 64
static struct sigaction old_sigaction;
static unsigned n_installed = 0;
/* We maintain a fixed size list of page addresses that triggered a
SIGBUS. We access with list with atomic operations, so that we
don't have to deal with locks between signal handler and main
programs in possibly multiple threads. */
static void* volatile sigbus_queue[SIGBUS_QUEUE_MAX];
static volatile sig_atomic_t n_sigbus_queue = 0;
static void sigbus_push(void *addr) {
unsigned u;
assert(addr);
/* Find a free place, increase the number of entries and leave, if we can */
for (u = 0; u < SIGBUS_QUEUE_MAX; u++)
if (__sync_bool_compare_and_swap(&sigbus_queue[u], NULL, addr)) {
__sync_fetch_and_add(&n_sigbus_queue, 1);
return;
}
/* If we can't, make sure the queue size is out of bounds, to
* mark it as overflow */
for (;;) {
unsigned c;
__sync_synchronize();
c = n_sigbus_queue;
if (c > SIGBUS_QUEUE_MAX) /* already overflow */
return;
if (__sync_bool_compare_and_swap(&n_sigbus_queue, c, c + SIGBUS_QUEUE_MAX))
return;
}
}
int sigbus_pop(void **ret) {
assert(ret);
for (;;) {
unsigned u, c;
__sync_synchronize();
c = n_sigbus_queue;
if (_likely_(c == 0))
return 0;
if (_unlikely_(c >= SIGBUS_QUEUE_MAX))
return -EOVERFLOW;
for (u = 0; u < SIGBUS_QUEUE_MAX; u++) {
void *addr;
addr = sigbus_queue[u];
if (!addr)
continue;
if (__sync_bool_compare_and_swap(&sigbus_queue[u], addr, NULL)) {
__sync_fetch_and_sub(&n_sigbus_queue, 1);
*ret = addr;
return 1;
}
}
}
}
static void sigbus_handler(int sn, siginfo_t *si, void *data) {
unsigned long ul;
void *aligned;
assert(sn == SIGBUS);
assert(si);
if (si->si_code != BUS_ADRERR || !si->si_addr) {
assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0);
raise(SIGBUS);
return;
}
ul = (unsigned long) si->si_addr;
ul = ul / page_size();
ul = ul * page_size();
aligned = (void*) ul;
/* Let's remember which address failed */
sigbus_push(aligned);
/* Replace mapping with an anonymous page, so that the
* execution can continue, however with a zeroed out page */
assert_se(mmap(aligned, page_size(), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0) == aligned);
}
void sigbus_install(void) {
struct sigaction sa = {
.sa_sigaction = sigbus_handler,
.sa_flags = SA_SIGINFO,
};
n_installed++;
if (n_installed == 1)
assert_se(sigaction(SIGBUS, &sa, &old_sigaction) == 0);
return;
}
void sigbus_reset(void) {
if (n_installed <= 0)
return;
n_installed--;
if (n_installed == 0)
assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0);
return;
}
|
