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-rw-r--r--src/basic/sigbus.c151
1 files changed, 151 insertions, 0 deletions
diff --git a/src/basic/sigbus.c b/src/basic/sigbus.c
new file mode 100644
index 0000000..33e2045
--- /dev/null
+++ b/src/basic/sigbus.c
@@ -0,0 +1,151 @@
+/* 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"
+
+#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 overflowed */
+ for (;;) {
+ sig_atomic_t c;
+
+ __atomic_thread_fence(__ATOMIC_SEQ_CST);
+ c = n_sigbus_queue;
+
+ if (c > SIGBUS_QUEUE_MAX) /* already overflowed */
+ 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);
+ rt_sigqueueinfo(getpid_cached(), SIGBUS, 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;
+}