diff options
Diffstat (limited to 'src/shared')
| -rw-r--r-- | src/shared/sigbus.c | 152 | ||||
| -rw-r--r-- | src/shared/sigbus.h | 25 |
2 files changed, 177 insertions, 0 deletions
diff --git a/src/shared/sigbus.c b/src/shared/sigbus.c new file mode 100644 index 0000000000..0108603fe8 --- /dev/null +++ b/src/shared/sigbus.c @@ -0,0 +1,152 @@ +/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/ + +/*** + This file is part of systemd. + + Copyright 2014 Lennart Poettering + + systemd is free software; you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 2.1 of the License, or + (at your option) any later version. + + systemd is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with systemd; If not, see <http://www.gnu.org/licenses/>. +***/ + +#include <signal.h> +#include <sys/mman.h> + +#include "macro.h" +#include "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) { + unsigned u; + + assert(addr); + + /* Find a free place, increase the number of entries and leave, if we can */ + for (u = 0; u < SIGBUS_QUEUE_MAX; u++) + if (__sync_bool_compare_and_swap(&sigbus_queue[u], NULL, addr)) { + __sync_fetch_and_add(&n_sigbus_queue, 1); + return; + } + + /* If we can't, make sure the queue size is out of bounds, to + * mark it as overflow */ + for (;;) { + unsigned c; + + __sync_synchronize(); + c = n_sigbus_queue; + + if (c > SIGBUS_QUEUE_MAX) /* already overflow */ + return; + + if (__sync_bool_compare_and_swap(&n_sigbus_queue, c, c + SIGBUS_QUEUE_MAX)) + return; + } +} + +int sigbus_pop(void **ret) { + assert(ret); + + for (;;) { + unsigned u, c; + + __sync_synchronize(); + 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; + + if (__sync_bool_compare_and_swap(&sigbus_queue[u], addr, NULL)) { + __sync_fetch_and_sub(&n_sigbus_queue, 1); + *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); + raise(SIGBUS); + 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, + }; + + 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; +} diff --git a/src/shared/sigbus.h b/src/shared/sigbus.h new file mode 100644 index 0000000000..25593af2d4 --- /dev/null +++ b/src/shared/sigbus.h @@ -0,0 +1,25 @@ +/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/ + +/*** + This file is part of systemd. + + Copyright 2014 Lennart Poettering + + systemd is free software; you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 2.1 of the License, or + (at your option) any later version. + + systemd is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with systemd; If not, see <http://www.gnu.org/licenses/>. +***/ + +void sigbus_install(void); +void sigbus_reset(void); + +int sigbus_pop(void **ret); |