futex: Split out syscalls

Put the syscalls in their own little file.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: André Almeida <andrealmeid@collabora.com>
Link: https://lore.kernel.org/r/20210923171111.300673-3-andrealmeid@collabora.com

include/linux/syscalls.h

@@ -610,7 +610,7 @@ asmlinkage long sys_waitid(int which, pid_t pid,
 asmlinkage long sys_set_tid_address(int __user *tidptr);
 asmlinkage long sys_unshare(unsigned long unshare_flags);
 
-/* kernel/futex.c */
+/* kernel/futex/syscalls.c */
 asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
 			  const struct __kernel_timespec __user *utime,
 			  u32 __user *uaddr2, u32 val3);

kernel/futex/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
-obj-y += core.o
+obj-y += core.o syscalls.o

kernel/futex/futex.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _FUTEX_H
+#define _FUTEX_H
+
+#include <asm/futex.h>
+
+/*
+ * Futex flags used to encode options to functions and preserve them across
+ * restarts.
+ */
+#ifdef CONFIG_MMU
+# define FLAGS_SHARED		0x01
+#else
+/*
+ * NOMMU does not have per process address space. Let the compiler optimize
+ * code away.
+ */
+# define FLAGS_SHARED		0x00
+#endif
+#define FLAGS_CLOCKRT		0x02
+#define FLAGS_HAS_TIMEOUT	0x04
+
+#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
+#define futex_cmpxchg_enabled 1
+#else
+extern int  __read_mostly futex_cmpxchg_enabled;
+#endif
+
+#ifdef CONFIG_FAIL_FUTEX
+extern bool should_fail_futex(bool fshared);
+#else
+static inline bool should_fail_futex(bool fshared)
+{
+	return false;
+}
+#endif
+
+extern int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, u32
+				 val, ktime_t *abs_time, u32 bitset, u32 __user
+				 *uaddr2);
+
+extern int futex_requeue(u32 __user *uaddr1, unsigned int flags,
+			 u32 __user *uaddr2, int nr_wake, int nr_requeue,
+			 u32 *cmpval, int requeue_pi);
+
+extern int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
+		      ktime_t *abs_time, u32 bitset);
+
+extern int futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset);
+
+extern int futex_wake_op(u32 __user *uaddr1, unsigned int flags,
+			 u32 __user *uaddr2, int nr_wake, int nr_wake2, int op);
+
+extern int futex_unlock_pi(u32 __user *uaddr, unsigned int flags);
+
+extern int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int trylock);
+
+#endif /* _FUTEX_H */

kernel/futex/syscalls.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/compat.h>
+#include <linux/syscalls.h>
+#include <linux/time_namespace.h>
+
+#include "futex.h"
+
+/*
+ * Support for robust futexes: the kernel cleans up held futexes at
+ * thread exit time.
+ *
+ * Implementation: user-space maintains a per-thread list of locks it
+ * is holding. Upon do_exit(), the kernel carefully walks this list,
+ * and marks all locks that are owned by this thread with the
+ * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
+ * always manipulated with the lock held, so the list is private and
+ * per-thread. Userspace also maintains a per-thread 'list_op_pending'
+ * field, to allow the kernel to clean up if the thread dies after
+ * acquiring the lock, but just before it could have added itself to
+ * the list. There can only be one such pending lock.
+ */
+
+/**
+ * sys_set_robust_list() - Set the robust-futex list head of a task
+ * @head:	pointer to the list-head
+ * @len:	length of the list-head, as userspace expects
+ */
+SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
+		size_t, len)
+{
+	if (!futex_cmpxchg_enabled)
+		return -ENOSYS;
+	/*
+	 * The kernel knows only one size for now:
+	 */
+	if (unlikely(len != sizeof(*head)))
+		return -EINVAL;
+
+	current->robust_list = head;
+
+	return 0;
+}
+
+/**
+ * sys_get_robust_list() - Get the robust-futex list head of a task
+ * @pid:	pid of the process [zero for current task]
+ * @head_ptr:	pointer to a list-head pointer, the kernel fills it in
+ * @len_ptr:	pointer to a length field, the kernel fills in the header size
+ */
+SYSCALL_DEFINE3(get_robust_list, int, pid,
+		struct robust_list_head __user * __user *, head_ptr,
+		size_t __user *, len_ptr)
+{
+	struct robust_list_head __user *head;
+	unsigned long ret;
+	struct task_struct *p;
+
+	if (!futex_cmpxchg_enabled)
+		return -ENOSYS;
+
+	rcu_read_lock();
+
+	ret = -ESRCH;
+	if (!pid)
+		p = current;
+	else {
+		p = find_task_by_vpid(pid);
+		if (!p)
+			goto err_unlock;
+	}
+
+	ret = -EPERM;
+	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
+		goto err_unlock;
+
+	head = p->robust_list;
+	rcu_read_unlock();
+
+	if (put_user(sizeof(*head), len_ptr))
+		return -EFAULT;
+	return put_user(head, head_ptr);
+
+err_unlock:
+	rcu_read_unlock();
+
+	return ret;
+}
+
+long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
+		u32 __user *uaddr2, u32 val2, u32 val3)
+{
+	int cmd = op & FUTEX_CMD_MASK;
+	unsigned int flags = 0;
+
+	if (!(op & FUTEX_PRIVATE_FLAG))
+		flags |= FLAGS_SHARED;
+
+	if (op & FUTEX_CLOCK_REALTIME) {
+		flags |= FLAGS_CLOCKRT;
+		if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
+		    cmd != FUTEX_LOCK_PI2)
+			return -ENOSYS;
+	}
+
+	switch (cmd) {
+	case FUTEX_LOCK_PI:
+	case FUTEX_LOCK_PI2:
+	case FUTEX_UNLOCK_PI:
+	case FUTEX_TRYLOCK_PI:
+	case FUTEX_WAIT_REQUEUE_PI:
+	case FUTEX_CMP_REQUEUE_PI:
+		if (!futex_cmpxchg_enabled)
+			return -ENOSYS;
+	}
+
+	switch (cmd) {
+	case FUTEX_WAIT:
+		val3 = FUTEX_BITSET_MATCH_ANY;
+		fallthrough;
+	case FUTEX_WAIT_BITSET:
+		return futex_wait(uaddr, flags, val, timeout, val3);
+	case FUTEX_WAKE:
+		val3 = FUTEX_BITSET_MATCH_ANY;
+		fallthrough;
+	case FUTEX_WAKE_BITSET:
+		return futex_wake(uaddr, flags, val, val3);
+	case FUTEX_REQUEUE:
+		return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
+	case FUTEX_CMP_REQUEUE:
+		return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
+	case FUTEX_WAKE_OP:
+		return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
+	case FUTEX_LOCK_PI:
+		flags |= FLAGS_CLOCKRT;
+		fallthrough;
+	case FUTEX_LOCK_PI2:
+		return futex_lock_pi(uaddr, flags, timeout, 0);
+	case FUTEX_UNLOCK_PI:
+		return futex_unlock_pi(uaddr, flags);
+	case FUTEX_TRYLOCK_PI:
+		return futex_lock_pi(uaddr, flags, NULL, 1);
+	case FUTEX_WAIT_REQUEUE_PI:
+		val3 = FUTEX_BITSET_MATCH_ANY;
+		return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
+					     uaddr2);
+	case FUTEX_CMP_REQUEUE_PI:
+		return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
+	}
+	return -ENOSYS;
+}
+
+static __always_inline bool futex_cmd_has_timeout(u32 cmd)
+{
+	switch (cmd) {
+	case FUTEX_WAIT:
+	case FUTEX_LOCK_PI:
+	case FUTEX_LOCK_PI2:
+	case FUTEX_WAIT_BITSET:
+	case FUTEX_WAIT_REQUEUE_PI:
+		return true;
+	}
+	return false;
+}
+
+static __always_inline int
+futex_init_timeout(u32 cmd, u32 op, struct timespec64 *ts, ktime_t *t)
+{
+	if (!timespec64_valid(ts))
+		return -EINVAL;
+
+	*t = timespec64_to_ktime(*ts);
+	if (cmd == FUTEX_WAIT)
+		*t = ktime_add_safe(ktime_get(), *t);
+	else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME))
+		*t = timens_ktime_to_host(CLOCK_MONOTONIC, *t);
+	return 0;
+}
+
+SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
+		const struct __kernel_timespec __user *, utime,
+		u32 __user *, uaddr2, u32, val3)
+{
+	int ret, cmd = op & FUTEX_CMD_MASK;
+	ktime_t t, *tp = NULL;
+	struct timespec64 ts;
+
+	if (utime && futex_cmd_has_timeout(cmd)) {
+		if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
+			return -EFAULT;
+		if (get_timespec64(&ts, utime))
+			return -EFAULT;
+		ret = futex_init_timeout(cmd, op, &ts, &t);
+		if (ret)
+			return ret;
+		tp = &t;
+	}
+
+	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
+}
+
+#ifdef CONFIG_COMPAT
+COMPAT_SYSCALL_DEFINE2(set_robust_list,
+		struct compat_robust_list_head __user *, head,
+		compat_size_t, len)
+{
+	if (!futex_cmpxchg_enabled)
+		return -ENOSYS;
+
+	if (unlikely(len != sizeof(*head)))
+		return -EINVAL;
+
+	current->compat_robust_list = head;
+
+	return 0;
+}
+
+COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
+			compat_uptr_t __user *, head_ptr,
+			compat_size_t __user *, len_ptr)
+{
+	struct compat_robust_list_head __user *head;
+	unsigned long ret;
+	struct task_struct *p;
+
+	if (!futex_cmpxchg_enabled)
+		return -ENOSYS;
+
+	rcu_read_lock();
+
+	ret = -ESRCH;
+	if (!pid)
+		p = current;
+	else {
+		p = find_task_by_vpid(pid);
+		if (!p)
+			goto err_unlock;
+	}
+
+	ret = -EPERM;
+	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
+		goto err_unlock;
+
+	head = p->compat_robust_list;
+	rcu_read_unlock();
+
+	if (put_user(sizeof(*head), len_ptr))
+		return -EFAULT;
+	return put_user(ptr_to_compat(head), head_ptr);
+
+err_unlock:
+	rcu_read_unlock();
+
+	return ret;
+}
+#endif /* CONFIG_COMPAT */
+
+#ifdef CONFIG_COMPAT_32BIT_TIME
+SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
+		const struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
+		u32, val3)
+{
+	int ret, cmd = op & FUTEX_CMD_MASK;
+	ktime_t t, *tp = NULL;
+	struct timespec64 ts;
+
+	if (utime && futex_cmd_has_timeout(cmd)) {
+		if (get_old_timespec32(&ts, utime))
+			return -EFAULT;
+		ret = futex_init_timeout(cmd, op, &ts, &t);
+		if (ret)
+			return ret;
+		tp = &t;
+	}
+
+	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
+}
+#endif /* CONFIG_COMPAT_32BIT_TIME */
+

kernel/sys_ni.c

@@ -143,7 +143,7 @@ COND_SYSCALL(capset);
 /* __ARCH_WANT_SYS_CLONE3 */
 COND_SYSCALL(clone3);
 
-/* kernel/futex.c */
+/* kernel/futex/syscalls.c */
 COND_SYSCALL(futex);
 COND_SYSCALL(futex_time32);
 COND_SYSCALL(set_robust_list);