140 lines
3.8 KiB
C
140 lines
3.8 KiB
C
/* SPDX-License-Identifier: LGPL-2.1+ */
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#include <errno.h>
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#include <signal.h>
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#include <stddef.h>
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#include <sys/mman.h>
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#include "macro.h"
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#include "sigbus.h"
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#include "util.h"
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#define SIGBUS_QUEUE_MAX 64
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static struct sigaction old_sigaction;
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static unsigned n_installed = 0;
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/* We maintain a fixed size list of page addresses that triggered a
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SIGBUS. We access with list with atomic operations, so that we
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don't have to deal with locks between signal handler and main
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programs in possibly multiple threads. */
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static void* volatile sigbus_queue[SIGBUS_QUEUE_MAX];
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static volatile sig_atomic_t n_sigbus_queue = 0;
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static void sigbus_push(void *addr) {
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unsigned u;
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assert(addr);
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/* Find a free place, increase the number of entries and leave, if we can */
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for (u = 0; u < SIGBUS_QUEUE_MAX; u++)
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if (__sync_bool_compare_and_swap(&sigbus_queue[u], NULL, addr)) {
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__sync_fetch_and_add(&n_sigbus_queue, 1);
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return;
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}
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/* If we can't, make sure the queue size is out of bounds, to
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* mark it as overflow */
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for (;;) {
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unsigned c;
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__sync_synchronize();
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c = n_sigbus_queue;
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if (c > SIGBUS_QUEUE_MAX) /* already overflow */
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return;
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if (__sync_bool_compare_and_swap(&n_sigbus_queue, c, c + SIGBUS_QUEUE_MAX))
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return;
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}
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}
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int sigbus_pop(void **ret) {
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assert(ret);
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for (;;) {
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unsigned u, c;
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__sync_synchronize();
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c = n_sigbus_queue;
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if (_likely_(c == 0))
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return 0;
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if (_unlikely_(c >= SIGBUS_QUEUE_MAX))
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return -EOVERFLOW;
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for (u = 0; u < SIGBUS_QUEUE_MAX; u++) {
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void *addr;
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addr = sigbus_queue[u];
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if (!addr)
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continue;
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if (__sync_bool_compare_and_swap(&sigbus_queue[u], addr, NULL)) {
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__sync_fetch_and_sub(&n_sigbus_queue, 1);
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*ret = addr;
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return 1;
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}
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}
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}
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}
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static void sigbus_handler(int sn, siginfo_t *si, void *data) {
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unsigned long ul;
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void *aligned;
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assert(sn == SIGBUS);
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assert(si);
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if (si->si_code != BUS_ADRERR || !si->si_addr) {
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assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0);
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raise(SIGBUS);
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return;
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}
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ul = (unsigned long) si->si_addr;
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ul = ul / page_size();
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ul = ul * page_size();
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aligned = (void*) ul;
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/* Let's remember which address failed */
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sigbus_push(aligned);
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/* Replace mapping with an anonymous page, so that the
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* execution can continue, however with a zeroed out page */
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assert_se(mmap(aligned, page_size(), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0) == aligned);
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}
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void sigbus_install(void) {
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struct sigaction sa = {
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.sa_sigaction = sigbus_handler,
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.sa_flags = SA_SIGINFO,
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};
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/* make sure that sysconf() is not called from a signal handler because
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* it is not guaranteed to be async-signal-safe since POSIX.1-2008 */
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(void) page_size();
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n_installed++;
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if (n_installed == 1)
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assert_se(sigaction(SIGBUS, &sa, &old_sigaction) == 0);
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return;
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}
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void sigbus_reset(void) {
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if (n_installed <= 0)
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return;
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n_installed--;
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if (n_installed == 0)
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assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0);
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return;
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}
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