| /* SPDX-License-Identifier: LGPL-2.1-or-later */ |
| |
| #include <errno.h> |
| #include <signal.h> |
| #include <stddef.h> |
| #include <sys/mman.h> |
| |
| #include "macro.h" |
| #include "memory-util.h" |
| #include "missing_syscall.h" |
| #include "process-util.h" |
| #include "sigbus.h" |
| #include "signal-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) { |
| assert(addr); |
| |
| /* Find a free place, increase the number of entries and leave, if we can */ |
| for (size_t u = 0; u < SIGBUS_QUEUE_MAX; u++) { |
| /* OK to initialize this here since we haven't started the atomic ops yet */ |
| void *tmp = NULL; |
| if (__atomic_compare_exchange_n(&sigbus_queue[u], &tmp, addr, false, |
| __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)) { |
| __atomic_fetch_add(&n_sigbus_queue, 1, __ATOMIC_SEQ_CST); |
| return; |
| } |
| } |
| |
| /* If we can't, make sure the queue size is out of bounds, to |
| * mark it as overflow */ |
| for (;;) { |
| sig_atomic_t c; |
| |
| __atomic_thread_fence(__ATOMIC_SEQ_CST); |
| c = n_sigbus_queue; |
| |
| if (c > SIGBUS_QUEUE_MAX) /* already overflow */ |
| return; |
| |
| /* OK if we clobber c here, since we either immediately return |
| * or it will be immediately reinitialized on next loop */ |
| if (__atomic_compare_exchange_n(&n_sigbus_queue, &c, c + SIGBUS_QUEUE_MAX, false, |
| __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)) |
| return; |
| } |
| } |
| |
| int sigbus_pop(void **ret) { |
| assert(ret); |
| |
| for (;;) { |
| unsigned u, c; |
| |
| __atomic_thread_fence(__ATOMIC_SEQ_CST); |
| 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; |
| |
| /* OK if we clobber addr here, since we either immediately return |
| * or it will be immediately reinitialized on next loop */ |
| if (__atomic_compare_exchange_n(&sigbus_queue[u], &addr, NULL, false, |
| __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)) { |
| __atomic_fetch_sub(&n_sigbus_queue, 1, __ATOMIC_SEQ_CST); |
| /* If we successfully entered this if condition, addr won't |
| * have been modified since its assignment, so safe to use it */ |
| *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); |
| propagate_signal(sn, si); |
| 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, |
| }; |
| |
| /* make sure that sysconf() is not called from a signal handler because |
| * it is not guaranteed to be async-signal-safe since POSIX.1-2008 */ |
| (void) page_size(); |
| |
| 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; |
| } |