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