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Commit | Line | Data |
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53e1b683 | 1 | /* SPDX-License-Identifier: LGPL-2.1+ */ |
fa6ac760 | 2 | |
11c3a366 | 3 | #include <errno.h> |
fa6ac760 | 4 | #include <signal.h> |
11c3a366 | 5 | #include <stddef.h> |
fa6ac760 LP |
6 | #include <sys/mman.h> |
7 | ||
8 | #include "macro.h" | |
fa6ac760 | 9 | #include "sigbus.h" |
cf0fbc49 | 10 | #include "util.h" |
fa6ac760 LP |
11 | |
12 | #define SIGBUS_QUEUE_MAX 64 | |
13 | ||
14 | static struct sigaction old_sigaction; | |
15 | static unsigned n_installed = 0; | |
16 | ||
17 | /* We maintain a fixed size list of page addresses that triggered a | |
18 | SIGBUS. We access with list with atomic operations, so that we | |
19 | don't have to deal with locks between signal handler and main | |
20 | programs in possibly multiple threads. */ | |
21 | ||
22 | static void* volatile sigbus_queue[SIGBUS_QUEUE_MAX]; | |
23 | static volatile sig_atomic_t n_sigbus_queue = 0; | |
24 | ||
25 | static void sigbus_push(void *addr) { | |
26 | unsigned u; | |
27 | ||
28 | assert(addr); | |
29 | ||
30 | /* Find a free place, increase the number of entries and leave, if we can */ | |
31 | for (u = 0; u < SIGBUS_QUEUE_MAX; u++) | |
32 | if (__sync_bool_compare_and_swap(&sigbus_queue[u], NULL, addr)) { | |
33 | __sync_fetch_and_add(&n_sigbus_queue, 1); | |
34 | return; | |
35 | } | |
36 | ||
37 | /* If we can't, make sure the queue size is out of bounds, to | |
38 | * mark it as overflow */ | |
39 | for (;;) { | |
40 | unsigned c; | |
41 | ||
42 | __sync_synchronize(); | |
43 | c = n_sigbus_queue; | |
44 | ||
45 | if (c > SIGBUS_QUEUE_MAX) /* already overflow */ | |
46 | return; | |
47 | ||
48 | if (__sync_bool_compare_and_swap(&n_sigbus_queue, c, c + SIGBUS_QUEUE_MAX)) | |
49 | return; | |
50 | } | |
51 | } | |
52 | ||
53 | int sigbus_pop(void **ret) { | |
54 | assert(ret); | |
55 | ||
56 | for (;;) { | |
57 | unsigned u, c; | |
58 | ||
59 | __sync_synchronize(); | |
60 | c = n_sigbus_queue; | |
61 | ||
62 | if (_likely_(c == 0)) | |
63 | return 0; | |
64 | ||
65 | if (_unlikely_(c >= SIGBUS_QUEUE_MAX)) | |
66 | return -EOVERFLOW; | |
67 | ||
68 | for (u = 0; u < SIGBUS_QUEUE_MAX; u++) { | |
69 | void *addr; | |
70 | ||
71 | addr = sigbus_queue[u]; | |
72 | if (!addr) | |
73 | continue; | |
74 | ||
75 | if (__sync_bool_compare_and_swap(&sigbus_queue[u], addr, NULL)) { | |
76 | __sync_fetch_and_sub(&n_sigbus_queue, 1); | |
77 | *ret = addr; | |
78 | return 1; | |
79 | } | |
80 | } | |
81 | } | |
82 | } | |
83 | ||
84 | static void sigbus_handler(int sn, siginfo_t *si, void *data) { | |
85 | unsigned long ul; | |
86 | void *aligned; | |
87 | ||
88 | assert(sn == SIGBUS); | |
89 | assert(si); | |
90 | ||
91 | if (si->si_code != BUS_ADRERR || !si->si_addr) { | |
92 | assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0); | |
93 | raise(SIGBUS); | |
94 | return; | |
95 | } | |
96 | ||
97 | ul = (unsigned long) si->si_addr; | |
98 | ul = ul / page_size(); | |
99 | ul = ul * page_size(); | |
100 | aligned = (void*) ul; | |
101 | ||
102 | /* Let's remember which address failed */ | |
103 | sigbus_push(aligned); | |
104 | ||
105 | /* Replace mapping with an anonymous page, so that the | |
106 | * execution can continue, however with a zeroed out page */ | |
107 | assert_se(mmap(aligned, page_size(), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0) == aligned); | |
108 | } | |
109 | ||
110 | void sigbus_install(void) { | |
111 | struct sigaction sa = { | |
112 | .sa_sigaction = sigbus_handler, | |
113 | .sa_flags = SA_SIGINFO, | |
114 | }; | |
115 | ||
1595b257 D |
116 | /* make sure that sysconf() is not called from a signal handler because |
117 | * it is not guaranteed to be async-signal-safe since POSIX.1-2008 */ | |
118 | (void) page_size(); | |
119 | ||
fa6ac760 LP |
120 | n_installed++; |
121 | ||
122 | if (n_installed == 1) | |
123 | assert_se(sigaction(SIGBUS, &sa, &old_sigaction) == 0); | |
124 | ||
125 | return; | |
126 | } | |
127 | ||
128 | void sigbus_reset(void) { | |
129 | ||
130 | if (n_installed <= 0) | |
131 | return; | |
132 | ||
133 | n_installed--; | |
134 | ||
135 | if (n_installed == 0) | |
136 | assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0); | |
137 | ||
138 | return; | |
139 | } |