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- /* Copyright (C) 2014 Stony Brook University
- This file is part of Graphene Library OS.
- Graphene Library OS 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 3 of the
- License, or (at your option) any later version.
- Graphene Library OS 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 this program. If not, see <http://www.gnu.org/licenses/>. */
- /*
- * db_mutex.c
- *
- * This file contains APIs that provide operations of (futex based) mutexes.
- * Based on "Mutexes and Condition Variables using Futexes"
- * (http://locklessinc.com/articles/mutex_cv_futex)
- */
- #include <asm/errno.h>
- #include <atomic.h>
- #include <errno.h>
- #include <limits.h>
- #include <linux/futex.h>
- #include <linux/time.h>
- #include "api.h"
- #include "pal.h"
- #include "pal_debug.h"
- #include "pal_defs.h"
- #include "pal_error.h"
- #include "pal_internal.h"
- #include "pal_linux.h"
- #include "pal_linux_defs.h"
- #include "pal_linux_error.h"
- #define MUTEX_SPINLOCK_TIMES 100
- #define MUTEX_UNLOCKED 0
- #define MUTEX_LOCKED 1
- int _DkMutexCreate(PAL_HANDLE* handle, int initialCount) {
- PAL_HANDLE mut = malloc(HANDLE_SIZE(mutex));
- SET_HANDLE_TYPE(mut, mutex);
- atomic_set(&mut->mutex.mut.nwaiters, 0);
- mut->mutex.mut.locked = malloc_untrusted(sizeof(int64_t));
- if (!mut->mutex.mut.locked) {
- free(mut);
- return -PAL_ERROR_NOMEM;
- }
- *(mut->mutex.mut.locked) = initialCount;
- *handle = mut;
- return 0;
- }
- int _DkMutexLockTimeout(struct mutex_handle* m, int64_t timeout_us) {
- int ret = 0;
- if (MUTEX_UNLOCKED == cmpxchg(m->locked, MUTEX_UNLOCKED, MUTEX_LOCKED))
- goto success;
- if (timeout_us == 0) {
- ret = -PAL_ERROR_TRYAGAIN;
- goto out;
- }
- // Bump up the waiters count; we are probably going to block
- atomic_inc(&m->nwaiters);
- while (MUTEX_LOCKED == cmpxchg(m->locked, MUTEX_UNLOCKED, MUTEX_LOCKED)) {
- /*
- * Chia-Che 12/7/2017: m->locked points to untrusted memory, so
- * can be used for futex. Potentially this design may allow
- * attackers to change the mutex value and cause DoS.
- */
- ret = ocall_futex((int*)m->locked, FUTEX_WAIT, MUTEX_LOCKED, timeout_us);
- if (IS_ERR(ret)) {
- if (ERRNO(ret) == EWOULDBLOCK) {
- ret = -PAL_ERROR_TRYAGAIN;
- atomic_dec(&m->nwaiters);
- } else {
- ret = unix_to_pal_error(ERRNO(ret));
- atomic_dec(&m->nwaiters);
- }
- goto out;
- }
- }
- atomic_dec(&m->nwaiters);
- success:
- ret = 0;
- out:
- return ret;
- }
- int _DkMutexLock(struct mutex_handle* m) {
- return _DkMutexLockTimeout(m, -1);
- }
- int _DkMutexAcquireTimeout(PAL_HANDLE handle, int64_t timeout_us) {
- return _DkMutexLockTimeout(&handle->mutex.mut, timeout_us);
- }
- int _DkMutexUnlock(struct mutex_handle* m) {
- int ret = 0;
- int need_wake;
- /* Unlock */
- *(m->locked) = MUTEX_UNLOCKED; // TODO: this is not atomic!
- /* We need to make sure the write to locked is visible to lock-ers
- * before we read the waiter count. */
- MB();
- need_wake = atomic_read(&m->nwaiters);
- /* If we need to wake someone up... */
- if (need_wake)
- ocall_futex((int*)m->locked, FUTEX_WAKE, 1, -1);
- return ret;
- }
- void _DkMutexRelease(PAL_HANDLE handle) {
- struct mutex_handle* mut = &handle->mutex.mut;
- int ret = _DkMutexUnlock(mut);
- if (ret < 0)
- _DkRaiseFailure(ret);
- return;
- }
- static int mutex_wait(PAL_HANDLE handle, int64_t timeout_us) {
- return _DkMutexAcquireTimeout(handle, timeout_us);
- }
- static int mutex_close(PAL_HANDLE handle) {
- free_untrusted((int64_t*)handle->mutex.mut.locked);
- return 0;
- }
- struct handle_ops mutex_ops = {
- .wait = &mutex_wait,
- .close = &mutex_close,
- };
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