1/*
2 * signal.c: Register a sigaltstack for objtool, to be able to
3 * run a signal handler on a separate stack even if
4 * the main process stack has overflown. Print out
5 * stack overflow errors when this happens.
6 */
7#include <stdio.h>
8#include <stdlib.h>
9#include <signal.h>
10#include <unistd.h>
11#include <sys/resource.h>
12#include <string.h>
13
14#include <objtool/objtool.h>
15#include <objtool/warn.h>
16
17static unsigned long stack_limit;
18
19static bool is_stack_overflow(void *fault_addr)
20{
21 unsigned long fault = (unsigned long)fault_addr;
22
23 /* Check if fault is in the guard page just below the limit. */
24 return fault < stack_limit && fault >= stack_limit - 4096;
25}
26
27static void signal_handler(int sig_num, siginfo_t *info, void *context)
28{
29 struct sigaction sa_dfl = {0};
30 const char *sig_name;
31 char msg[256];
32 int msg_len;
33
34 switch (sig_num) {
35 case SIGSEGV: sig_name = "SIGSEGV"; break;
36 case SIGBUS: sig_name = "SIGBUS"; break;
37 case SIGILL: sig_name = "SIGILL"; break;
38 case SIGABRT: sig_name = "SIGABRT"; break;
39 default: sig_name = "Unknown signal"; break;
40 }
41
42 if (is_stack_overflow(info->si_addr)) {
43 msg_len = snprintf(msg, sizeof(msg),
44 "%s: error: %s: objtool stack overflow!\n",
45 objname, sig_name);
46 } else {
47 msg_len = snprintf(msg, sizeof(msg),
48 "%s: error: %s: objtool crash!\n",
49 objname, sig_name);
50 }
51
52 msg_len = write(STDERR_FILENO, msg, msg_len);
53
54 /* Re-raise the signal to trigger the core dump */
55 sa_dfl.sa_handler = SIG_DFL;
56 sigaction(sig_num, &sa_dfl, NULL);
57 raise(sig_num);
58}
59
60static int read_stack_limit(void)
61{
62 unsigned long stack_start, stack_end;
63 struct rlimit rlim;
64 char line[256];
65 int ret = 0;
66 FILE *fp;
67
68 if (getrlimit(RLIMIT_STACK, &rlim)) {
69 ERROR_GLIBC("getrlimit");
70 return -1;
71 }
72
73 fp = fopen("/proc/self/maps", "r");
74 if (!fp) {
75 ERROR_GLIBC("fopen");
76 return -1;
77 }
78
79 while (fgets(line, sizeof(line), fp)) {
80 if (strstr(line, "[stack]")) {
81 if (sscanf(line, "%lx-%lx", &stack_start, &stack_end) != 2) {
82 ERROR_GLIBC("sscanf");
83 ret = -1;
84 goto done;
85 }
86 stack_limit = stack_end - rlim.rlim_cur;
87 goto done;
88 }
89 }
90
91 ret = -1;
92 ERROR("/proc/self/maps: can't find [stack]");
93
94done:
95 fclose(fp);
96
97 return ret;
98}
99
100int init_signal_handler(void)
101{
102 int signals[] = {SIGSEGV, SIGBUS, SIGILL, SIGABRT};
103 struct sigaction sa;
104 stack_t ss;
105
106 if (read_stack_limit())
107 return -1;
108
109 ss.ss_sp = malloc(SIGSTKSZ);
110 if (!ss.ss_sp) {
111 ERROR_GLIBC("malloc");
112 return -1;
113 }
114 ss.ss_size = SIGSTKSZ;
115 ss.ss_flags = 0;
116
117 if (sigaltstack(&ss, NULL) == -1) {
118 ERROR_GLIBC("sigaltstack");
119 return -1;
120 }
121
122 sa.sa_sigaction = signal_handler;
123 sigemptyset(&sa.sa_mask);
124
125 sa.sa_flags = SA_ONSTACK | SA_SIGINFO;
126
127 for (int i = 0; i < ARRAY_SIZE(signals); i++) {
128 if (sigaction(signals[i], &sa, NULL) == -1) {
129 ERROR_GLIBC("sigaction");
130 return -1;
131 }
132 }
133
134 return 0;
135}
136

source code of linux/tools/objtool/signal.c