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Message-ID: <163377403733.25758.14960879861778154722.tip-bot2@tip-bot2>
Date: Sat, 09 Oct 2021 10:07:17 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
andrealmeid@...labora.com, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: locking/core] futex: Split out syscalls
The following commit has been merged into the locking/core branch of tip:
Commit-ID: af8cc9600bbf2251b04c56139f7c83f87c3f878a
Gitweb: https://git.kernel.org/tip/af8cc9600bbf2251b04c56139f7c83f87c3f878a
Author: Peter Zijlstra <peterz@...radead.org>
AuthorDate: Thu, 23 Sep 2021 14:10:51 -03:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 07 Oct 2021 13:51:07 +02:00
futex: Split out syscalls
Put the syscalls in their own little file.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: André Almeida <andrealmeid@...labora.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: André Almeida <andrealmeid@...labora.com>
Link: https://lore.kernel.org/r/20210923171111.300673-3-andrealmeid@collabora.com
---
include/linux/syscalls.h | 2 +-
kernel/futex/Makefile | 2 +-
kernel/futex/core.c | 532 ++++++++------------------------------
kernel/futex/futex.h | 58 ++++-
kernel/futex/syscalls.c | 279 ++++++++++++++++++++-
kernel/sys_ni.c | 2 +-
6 files changed, 455 insertions(+), 420 deletions(-)
create mode 100644 kernel/futex/futex.h
create mode 100644 kernel/futex/syscalls.c
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 252243c..2597968 100644
--- a/include/linux/syscalls.h
+++ b/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);
diff --git a/kernel/futex/Makefile b/kernel/futex/Makefile
index b89ba3f..ff9a960 100644
--- a/kernel/futex/Makefile
+++ b/kernel/futex/Makefile
@@ -1,3 +1,3 @@
# SPDX-License-Identifier: GPL-2.0
-obj-y += core.o
+obj-y += core.o syscalls.o
diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index f9bc9aa..69d9892 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -34,14 +34,12 @@
#include <linux/compat.h>
#include <linux/jhash.h>
#include <linux/pagemap.h>
-#include <linux/syscalls.h>
#include <linux/freezer.h>
#include <linux/memblock.h>
#include <linux/fault-inject.h>
-#include <linux/time_namespace.h>
-
-#include <asm/futex.h>
+#include <linux/slab.h>
+#include "futex.h"
#include "../locking/rtmutex_common.h"
/*
@@ -144,27 +142,10 @@
* double_lock_hb() and double_unlock_hb(), respectively.
*/
-#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
-#define futex_cmpxchg_enabled 1
-#else
-static int __read_mostly futex_cmpxchg_enabled;
+#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
+int __read_mostly futex_cmpxchg_enabled;
#endif
-/*
- * 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
/*
* Priority Inheritance state:
@@ -329,7 +310,7 @@ static int __init setup_fail_futex(char *str)
}
__setup("fail_futex=", setup_fail_futex);
-static bool should_fail_futex(bool fshared)
+bool should_fail_futex(bool fshared)
{
if (fail_futex.ignore_private && !fshared)
return false;
@@ -358,17 +339,8 @@ late_initcall(fail_futex_debugfs);
#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
-#else
-static inline bool should_fail_futex(bool fshared)
-{
- return false;
-}
#endif /* CONFIG_FAIL_FUTEX */
-#ifdef CONFIG_COMPAT
-static void compat_exit_robust_list(struct task_struct *curr);
-#endif
-
/*
* Reflects a new waiter being added to the waitqueue.
*/
@@ -1647,8 +1619,7 @@ double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
/*
* Wake up waiters matching bitset queued on this futex (uaddr).
*/
-static int
-futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
+int futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
{
struct futex_hash_bucket *hb;
struct futex_q *this, *next;
@@ -1743,9 +1714,8 @@ static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
* Wake up all waiters hashed on the physical page that is mapped
* to this virtual address:
*/
-static int
-futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
- int nr_wake, int nr_wake2, int op)
+int futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
+ int nr_wake, int nr_wake2, int op)
{
union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
struct futex_hash_bucket *hb1, *hb2;
@@ -2124,9 +2094,8 @@ futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
* - >=0 - on success, the number of tasks requeued or woken;
* - <0 - on error
*/
-static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
- u32 __user *uaddr2, int nr_wake, int nr_requeue,
- u32 *cmpval, int requeue_pi)
+int futex_requeue(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
+ int nr_wake, int nr_requeue, u32 *cmpval, int requeue_pi)
{
union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
int task_count = 0, ret;
@@ -2926,8 +2895,7 @@ retry_private:
return ret;
}
-static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
- ktime_t *abs_time, u32 bitset)
+int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, ktime_t *abs_time, u32 bitset)
{
struct hrtimer_sleeper timeout, *to;
struct restart_block *restart;
@@ -3015,8 +2983,7 @@ static long futex_wait_restart(struct restart_block *restart)
*
* Also serves as futex trylock_pi()'ing, and due semantics.
*/
-static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
- ktime_t *time, int trylock)
+int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int trylock)
{
struct hrtimer_sleeper timeout, *to;
struct task_struct *exiting = NULL;
@@ -3186,7 +3153,7 @@ uaddr_faulted:
* This is the in-kernel slowpath: we look up the PI state (if any),
* and do the rt-mutex unlock.
*/
-static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
+int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
{
u32 curval, uval, vpid = task_pid_vnr(current);
union futex_key key = FUTEX_KEY_INIT;
@@ -3403,9 +3370,9 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
* - 0 - On success;
* - <0 - On error
*/
-static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
- u32 val, ktime_t *abs_time, u32 bitset,
- u32 __user *uaddr2)
+int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
+ u32 val, ktime_t *abs_time, u32 bitset,
+ u32 __user *uaddr2)
{
struct hrtimer_sleeper timeout, *to;
struct rt_mutex_waiter rt_waiter;
@@ -3539,87 +3506,6 @@ out:
return ret;
}
-/*
- * 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;
-}
-
/* Constants for the pending_op argument of handle_futex_death */
#define HANDLE_DEATH_PENDING true
#define HANDLE_DEATH_LIST false
@@ -3821,227 +3707,16 @@ static void exit_robust_list(struct task_struct *curr)
}
}
-static void futex_cleanup(struct task_struct *tsk)
-{
- if (unlikely(tsk->robust_list)) {
- exit_robust_list(tsk);
- tsk->robust_list = NULL;
- }
-
#ifdef CONFIG_COMPAT
- if (unlikely(tsk->compat_robust_list)) {
- compat_exit_robust_list(tsk);
- tsk->compat_robust_list = NULL;
- }
-#endif
-
- if (unlikely(!list_empty(&tsk->pi_state_list)))
- exit_pi_state_list(tsk);
-}
-
-/**
- * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
- * @tsk: task to set the state on
- *
- * Set the futex exit state of the task lockless. The futex waiter code
- * observes that state when a task is exiting and loops until the task has
- * actually finished the futex cleanup. The worst case for this is that the
- * waiter runs through the wait loop until the state becomes visible.
- *
- * This is called from the recursive fault handling path in do_exit().
- *
- * This is best effort. Either the futex exit code has run already or
- * not. If the OWNER_DIED bit has been set on the futex then the waiter can
- * take it over. If not, the problem is pushed back to user space. If the
- * futex exit code did not run yet, then an already queued waiter might
- * block forever, but there is nothing which can be done about that.
- */
-void futex_exit_recursive(struct task_struct *tsk)
-{
- /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
- if (tsk->futex_state == FUTEX_STATE_EXITING)
- mutex_unlock(&tsk->futex_exit_mutex);
- tsk->futex_state = FUTEX_STATE_DEAD;
-}
-
-static void futex_cleanup_begin(struct task_struct *tsk)
-{
- /*
- * Prevent various race issues against a concurrent incoming waiter
- * including live locks by forcing the waiter to block on
- * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
- * attach_to_pi_owner().
- */
- mutex_lock(&tsk->futex_exit_mutex);
-
- /*
- * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
- *
- * This ensures that all subsequent checks of tsk->futex_state in
- * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
- * tsk->pi_lock held.
- *
- * It guarantees also that a pi_state which was queued right before
- * the state change under tsk->pi_lock by a concurrent waiter must
- * be observed in exit_pi_state_list().
- */
- raw_spin_lock_irq(&tsk->pi_lock);
- tsk->futex_state = FUTEX_STATE_EXITING;
- raw_spin_unlock_irq(&tsk->pi_lock);
-}
-
-static void futex_cleanup_end(struct task_struct *tsk, int state)
-{
- /*
- * Lockless store. The only side effect is that an observer might
- * take another loop until it becomes visible.
- */
- tsk->futex_state = state;
- /*
- * Drop the exit protection. This unblocks waiters which observed
- * FUTEX_STATE_EXITING to reevaluate the state.
- */
- mutex_unlock(&tsk->futex_exit_mutex);
-}
-
-void futex_exec_release(struct task_struct *tsk)
-{
- /*
- * The state handling is done for consistency, but in the case of
- * exec() there is no way to prevent further damage as the PID stays
- * the same. But for the unlikely and arguably buggy case that a
- * futex is held on exec(), this provides at least as much state
- * consistency protection which is possible.
- */
- futex_cleanup_begin(tsk);
- futex_cleanup(tsk);
- /*
- * Reset the state to FUTEX_STATE_OK. The task is alive and about
- * exec a new binary.
- */
- futex_cleanup_end(tsk, FUTEX_STATE_OK);
-}
-
-void futex_exit_release(struct task_struct *tsk)
-{
- futex_cleanup_begin(tsk);
- futex_cleanup(tsk);
- futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
-}
-
-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)
+static void __user *futex_uaddr(struct robust_list __user *entry,
+ compat_long_t futex_offset)
{
- 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;
- }
+ compat_uptr_t base = ptr_to_compat(entry);
+ void __user *uaddr = compat_ptr(base + futex_offset);
- return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
+ return uaddr;
}
-#ifdef CONFIG_COMPAT
/*
* Fetch a robust-list pointer. Bit 0 signals PI futexes:
*/
@@ -4058,15 +3733,6 @@ compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **ent
return 0;
}
-static void __user *futex_uaddr(struct robust_list __user *entry,
- compat_long_t futex_offset)
-{
- compat_uptr_t base = ptr_to_compat(entry);
- void __user *uaddr = compat_ptr(base + futex_offset);
-
- return uaddr;
-}
-
/*
* Walk curr->robust_list (very carefully, it's a userspace list!)
* and mark any locks found there dead, and notify any waiters.
@@ -4143,83 +3809,115 @@ static void compat_exit_robust_list(struct task_struct *curr)
handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
}
}
+#endif
-COMPAT_SYSCALL_DEFINE2(set_robust_list,
- struct compat_robust_list_head __user *, head,
- compat_size_t, len)
+static void futex_cleanup(struct task_struct *tsk)
{
- if (!futex_cmpxchg_enabled)
- return -ENOSYS;
-
- if (unlikely(len != sizeof(*head)))
- return -EINVAL;
+ if (unlikely(tsk->robust_list)) {
+ exit_robust_list(tsk);
+ tsk->robust_list = NULL;
+ }
- current->compat_robust_list = head;
+#ifdef CONFIG_COMPAT
+ if (unlikely(tsk->compat_robust_list)) {
+ compat_exit_robust_list(tsk);
+ tsk->compat_robust_list = NULL;
+ }
+#endif
- return 0;
+ if (unlikely(!list_empty(&tsk->pi_state_list)))
+ exit_pi_state_list(tsk);
}
-COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
- compat_uptr_t __user *, head_ptr,
- compat_size_t __user *, len_ptr)
+/**
+ * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
+ * @tsk: task to set the state on
+ *
+ * Set the futex exit state of the task lockless. The futex waiter code
+ * observes that state when a task is exiting and loops until the task has
+ * actually finished the futex cleanup. The worst case for this is that the
+ * waiter runs through the wait loop until the state becomes visible.
+ *
+ * This is called from the recursive fault handling path in do_exit().
+ *
+ * This is best effort. Either the futex exit code has run already or
+ * not. If the OWNER_DIED bit has been set on the futex then the waiter can
+ * take it over. If not, the problem is pushed back to user space. If the
+ * futex exit code did not run yet, then an already queued waiter might
+ * block forever, but there is nothing which can be done about that.
+ */
+void futex_exit_recursive(struct task_struct *tsk)
{
- 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);
+ /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
+ if (tsk->futex_state == FUTEX_STATE_EXITING)
+ mutex_unlock(&tsk->futex_exit_mutex);
+ tsk->futex_state = FUTEX_STATE_DEAD;
+}
-err_unlock:
- rcu_read_unlock();
+static void futex_cleanup_begin(struct task_struct *tsk)
+{
+ /*
+ * Prevent various race issues against a concurrent incoming waiter
+ * including live locks by forcing the waiter to block on
+ * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
+ * attach_to_pi_owner().
+ */
+ mutex_lock(&tsk->futex_exit_mutex);
- return ret;
+ /*
+ * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
+ *
+ * This ensures that all subsequent checks of tsk->futex_state in
+ * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
+ * tsk->pi_lock held.
+ *
+ * It guarantees also that a pi_state which was queued right before
+ * the state change under tsk->pi_lock by a concurrent waiter must
+ * be observed in exit_pi_state_list().
+ */
+ raw_spin_lock_irq(&tsk->pi_lock);
+ tsk->futex_state = FUTEX_STATE_EXITING;
+ raw_spin_unlock_irq(&tsk->pi_lock);
}
-#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)
+static void futex_cleanup_end(struct task_struct *tsk, int state)
{
- int ret, cmd = op & FUTEX_CMD_MASK;
- ktime_t t, *tp = NULL;
- struct timespec64 ts;
+ /*
+ * Lockless store. The only side effect is that an observer might
+ * take another loop until it becomes visible.
+ */
+ tsk->futex_state = state;
+ /*
+ * Drop the exit protection. This unblocks waiters which observed
+ * FUTEX_STATE_EXITING to reevaluate the state.
+ */
+ mutex_unlock(&tsk->futex_exit_mutex);
+}
- 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;
- }
+void futex_exec_release(struct task_struct *tsk)
+{
+ /*
+ * The state handling is done for consistency, but in the case of
+ * exec() there is no way to prevent further damage as the PID stays
+ * the same. But for the unlikely and arguably buggy case that a
+ * futex is held on exec(), this provides at least as much state
+ * consistency protection which is possible.
+ */
+ futex_cleanup_begin(tsk);
+ futex_cleanup(tsk);
+ /*
+ * Reset the state to FUTEX_STATE_OK. The task is alive and about
+ * exec a new binary.
+ */
+ futex_cleanup_end(tsk, FUTEX_STATE_OK);
+}
- return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
+void futex_exit_release(struct task_struct *tsk)
+{
+ futex_cleanup_begin(tsk);
+ futex_cleanup(tsk);
+ futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
}
-#endif /* CONFIG_COMPAT_32BIT_TIME */
static void __init futex_detect_cmpxchg(void)
{
diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
new file mode 100644
index 0000000..7bb4ca8
--- /dev/null
+++ b/kernel/futex/futex.h
@@ -0,0 +1,58 @@
+/* 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 */
diff --git a/kernel/futex/syscalls.c b/kernel/futex/syscalls.c
new file mode 100644
index 0000000..6e7e36c
--- /dev/null
+++ b/kernel/futex/syscalls.c
@@ -0,0 +1,279 @@
+// 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 */
+
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index f43d89d..13ee833 100644
--- a/kernel/sys_ni.c
+++ b/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);
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