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fa6ac760 LP |
1 | /*** |
2 | This file is part of systemd. | |
3 | ||
4 | Copyright 2014 Lennart Poettering | |
5 | ||
6 | systemd is free software; you can redistribute it and/or modify it | |
7 | under the terms of the GNU Lesser General Public License as published by | |
8 | the Free Software Foundation; either version 2.1 of the License, or | |
9 | (at your option) any later version. | |
10 | ||
11 | systemd is distributed in the hope that it will be useful, but | |
12 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
14 | Lesser General Public License for more details. | |
15 | ||
16 | You should have received a copy of the GNU Lesser General Public License | |
17 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
18 | ***/ | |
19 | ||
11c3a366 | 20 | #include <errno.h> |
fa6ac760 | 21 | #include <signal.h> |
11c3a366 | 22 | #include <stddef.h> |
fa6ac760 LP |
23 | #include <sys/mman.h> |
24 | ||
25 | #include "macro.h" | |
fa6ac760 | 26 | #include "sigbus.h" |
cf0fbc49 | 27 | #include "util.h" |
fa6ac760 LP |
28 | |
29 | #define SIGBUS_QUEUE_MAX 64 | |
30 | ||
31 | static struct sigaction old_sigaction; | |
32 | static unsigned n_installed = 0; | |
33 | ||
34 | /* We maintain a fixed size list of page addresses that triggered a | |
35 | SIGBUS. We access with list with atomic operations, so that we | |
36 | don't have to deal with locks between signal handler and main | |
37 | programs in possibly multiple threads. */ | |
38 | ||
39 | static void* volatile sigbus_queue[SIGBUS_QUEUE_MAX]; | |
40 | static volatile sig_atomic_t n_sigbus_queue = 0; | |
41 | ||
42 | static void sigbus_push(void *addr) { | |
43 | unsigned u; | |
44 | ||
45 | assert(addr); | |
46 | ||
47 | /* Find a free place, increase the number of entries and leave, if we can */ | |
48 | for (u = 0; u < SIGBUS_QUEUE_MAX; u++) | |
49 | if (__sync_bool_compare_and_swap(&sigbus_queue[u], NULL, addr)) { | |
50 | __sync_fetch_and_add(&n_sigbus_queue, 1); | |
51 | return; | |
52 | } | |
53 | ||
54 | /* If we can't, make sure the queue size is out of bounds, to | |
55 | * mark it as overflow */ | |
56 | for (;;) { | |
57 | unsigned c; | |
58 | ||
59 | __sync_synchronize(); | |
60 | c = n_sigbus_queue; | |
61 | ||
62 | if (c > SIGBUS_QUEUE_MAX) /* already overflow */ | |
63 | return; | |
64 | ||
65 | if (__sync_bool_compare_and_swap(&n_sigbus_queue, c, c + SIGBUS_QUEUE_MAX)) | |
66 | return; | |
67 | } | |
68 | } | |
69 | ||
70 | int sigbus_pop(void **ret) { | |
71 | assert(ret); | |
72 | ||
73 | for (;;) { | |
74 | unsigned u, c; | |
75 | ||
76 | __sync_synchronize(); | |
77 | c = n_sigbus_queue; | |
78 | ||
79 | if (_likely_(c == 0)) | |
80 | return 0; | |
81 | ||
82 | if (_unlikely_(c >= SIGBUS_QUEUE_MAX)) | |
83 | return -EOVERFLOW; | |
84 | ||
85 | for (u = 0; u < SIGBUS_QUEUE_MAX; u++) { | |
86 | void *addr; | |
87 | ||
88 | addr = sigbus_queue[u]; | |
89 | if (!addr) | |
90 | continue; | |
91 | ||
92 | if (__sync_bool_compare_and_swap(&sigbus_queue[u], addr, NULL)) { | |
93 | __sync_fetch_and_sub(&n_sigbus_queue, 1); | |
94 | *ret = addr; | |
95 | return 1; | |
96 | } | |
97 | } | |
98 | } | |
99 | } | |
100 | ||
101 | static void sigbus_handler(int sn, siginfo_t *si, void *data) { | |
102 | unsigned long ul; | |
103 | void *aligned; | |
104 | ||
105 | assert(sn == SIGBUS); | |
106 | assert(si); | |
107 | ||
108 | if (si->si_code != BUS_ADRERR || !si->si_addr) { | |
109 | assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0); | |
110 | raise(SIGBUS); | |
111 | return; | |
112 | } | |
113 | ||
114 | ul = (unsigned long) si->si_addr; | |
115 | ul = ul / page_size(); | |
116 | ul = ul * page_size(); | |
117 | aligned = (void*) ul; | |
118 | ||
119 | /* Let's remember which address failed */ | |
120 | sigbus_push(aligned); | |
121 | ||
122 | /* Replace mapping with an anonymous page, so that the | |
123 | * execution can continue, however with a zeroed out page */ | |
124 | assert_se(mmap(aligned, page_size(), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0) == aligned); | |
125 | } | |
126 | ||
127 | void sigbus_install(void) { | |
128 | struct sigaction sa = { | |
129 | .sa_sigaction = sigbus_handler, | |
130 | .sa_flags = SA_SIGINFO, | |
131 | }; | |
132 | ||
133 | n_installed++; | |
134 | ||
135 | if (n_installed == 1) | |
136 | assert_se(sigaction(SIGBUS, &sa, &old_sigaction) == 0); | |
137 | ||
138 | return; | |
139 | } | |
140 | ||
141 | void sigbus_reset(void) { | |
142 | ||
143 | if (n_installed <= 0) | |
144 | return; | |
145 | ||
146 | n_installed--; | |
147 | ||
148 | if (n_installed == 0) | |
149 | assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0); | |
150 | ||
151 | return; | |
152 | } |