xref: /linux-6.15/kernel/time/itimer.c (revision 68f99be2)

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 1992 Darren Senn
 */

/* These are all the functions necessary to implement itimers */

#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/syscalls.h>
#include <linux/time.h>
#include <linux/sched/signal.h>
#include <linux/sched/cputime.h>
#include <linux/posix-timers.h>
#include <linux/hrtimer.h>
#include <trace/events/timer.h>
#include <linux/compat.h>

#include <linux/uaccess.h>

/**
 * itimer_get_remtime - get remaining time for the timer
 *
 * @timer: the timer to read
 *
 * Returns the delta between the expiry time and now, which can be
 * less than zero or 1usec for an pending expired timer
 */
static struct timespec64 itimer_get_remtime(struct hrtimer *timer)
{
	ktime_t rem = __hrtimer_get_remaining(timer, true);

	/*
	 * Racy but safe: if the itimer expires after the above
	 * hrtimer_get_remtime() call but before this condition
	 * then we return 0 - which is correct.
	 */
	if (hrtimer_active(timer)) {
		if (rem <= 0)
			rem = NSEC_PER_USEC;
	} else
		rem = 0;

	return ktime_to_timespec64(rem);
}

static void get_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
			   struct itimerspec64 *const value)
{
	u64 val, interval;
	struct cpu_itimer *it = &tsk->signal->it[clock_id];

	spin_lock_irq(&tsk->sighand->siglock);

	val = it->expires;
	interval = it->incr;
	if (val) {
		u64 t, samples[CPUCLOCK_MAX];

		thread_group_sample_cputime(tsk, samples);
		t = samples[clock_id];

		if (val < t)
			/* about to fire */
			val = TICK_NSEC;
		else
			val -= t;
	}

	spin_unlock_irq(&tsk->sighand->siglock);

	value->it_value = ns_to_timespec64(val);
	value->it_interval = ns_to_timespec64(interval);
}

static int do_getitimer(int which, struct itimerspec64 *value)
{
	struct task_struct *tsk = current;

	switch (which) {
	case ITIMER_REAL:
		spin_lock_irq(&tsk->sighand->siglock);
		value->it_value = itimer_get_remtime(&tsk->signal->real_timer);
		value->it_interval =
			ktime_to_timespec64(tsk->signal->it_real_incr);
		spin_unlock_irq(&tsk->sighand->siglock);
		break;
	case ITIMER_VIRTUAL:
		get_cpu_itimer(tsk, CPUCLOCK_VIRT, value);
		break;
	case ITIMER_PROF:
		get_cpu_itimer(tsk, CPUCLOCK_PROF, value);
		break;
	default:
		return(-EINVAL);
	}
	return 0;
}

static int put_itimerval(struct __kernel_old_itimerval __user *o,
			 const struct itimerspec64 *i)
{
	struct __kernel_old_itimerval v;

	v.it_interval.tv_sec = i->it_interval.tv_sec;
	v.it_interval.tv_usec = i->it_interval.tv_nsec / NSEC_PER_USEC;
	v.it_value.tv_sec = i->it_value.tv_sec;
	v.it_value.tv_usec = i->it_value.tv_nsec / NSEC_PER_USEC;
	return copy_to_user(o, &v, sizeof(struct __kernel_old_itimerval)) ? -EFAULT : 0;
}


SYSCALL_DEFINE2(getitimer, int, which, struct __kernel_old_itimerval __user *, value)
{
	struct itimerspec64 get_buffer;
	int error = do_getitimer(which, &get_buffer);

	if (!error && put_itimerval(value, &get_buffer))
		error = -EFAULT;
	return error;
}

#if defined(CONFIG_COMPAT) || defined(CONFIG_ALPHA)
struct old_itimerval32 {
	struct old_timeval32	it_interval;
	struct old_timeval32	it_value;
};

static int put_old_itimerval32(struct old_itimerval32 __user *o,
			       const struct itimerspec64 *i)
{
	struct old_itimerval32 v32;

	v32.it_interval.tv_sec = i->it_interval.tv_sec;
	v32.it_interval.tv_usec = i->it_interval.tv_nsec / NSEC_PER_USEC;
	v32.it_value.tv_sec = i->it_value.tv_sec;
	v32.it_value.tv_usec = i->it_value.tv_nsec / NSEC_PER_USEC;
	return copy_to_user(o, &v32, sizeof(struct old_itimerval32)) ? -EFAULT : 0;
}

COMPAT_SYSCALL_DEFINE2(getitimer, int, which,
		       struct old_itimerval32 __user *, value)
{
	struct itimerspec64 get_buffer;
	int error = do_getitimer(which, &get_buffer);

	if (!error && put_old_itimerval32(value, &get_buffer))
		error = -EFAULT;
	return error;
}
#endif

/*
 * Invoked from dequeue_signal() when SIG_ALRM is delivered.
 *
 * Restart the ITIMER_REAL timer if it is armed as periodic timer.  Doing
 * this in the signal delivery path instead of self rearming prevents a DoS
 * with small increments in the high reolution timer case and reduces timer
 * noise in general.
 */
void posixtimer_rearm_itimer(struct task_struct *tsk)
{
	struct hrtimer *tmr = &tsk->signal->real_timer;

	if (!hrtimer_is_queued(tmr) && tsk->signal->it_real_incr != 0) {
		hrtimer_forward(tmr, tmr->base->get_time(),
				tsk->signal->it_real_incr);
		hrtimer_restart(tmr);
	}
}

/*
 * Interval timers are restarted in the signal delivery path.  See
 * posixtimer_rearm_itimer().
 */
enum hrtimer_restart it_real_fn(struct hrtimer *timer)
{
	struct signal_struct *sig =
		container_of(timer, struct signal_struct, real_timer);
	struct pid *leader_pid = sig->pids[PIDTYPE_TGID];

	trace_itimer_expire(ITIMER_REAL, leader_pid, 0);
	kill_pid_info(SIGALRM, SEND_SIG_PRIV, leader_pid);

	return HRTIMER_NORESTART;
}

static void set_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
			   const struct itimerspec64 *const value,
			   struct itimerspec64 *const ovalue)
{
	u64 oval, nval, ointerval, ninterval;
	struct cpu_itimer *it = &tsk->signal->it[clock_id];

	nval = timespec64_to_ns(&value->it_value);
	ninterval = timespec64_to_ns(&value->it_interval);

	spin_lock_irq(&tsk->sighand->siglock);

	oval = it->expires;
	ointerval = it->incr;
	if (oval || nval) {
		if (nval > 0)
			nval += TICK_NSEC;
		set_process_cpu_timer(tsk, clock_id, &nval, &oval);
	}
	it->expires = nval;
	it->incr = ninterval;
	trace_itimer_state(clock_id == CPUCLOCK_VIRT ?
			   ITIMER_VIRTUAL : ITIMER_PROF, value, nval);

	spin_unlock_irq(&tsk->sighand->siglock);

	if (ovalue) {
		ovalue->it_value = ns_to_timespec64(oval);
		ovalue->it_interval = ns_to_timespec64(ointerval);
	}
}

/*
 * Returns true if the timeval is in canonical form
 */
#define timeval_valid(t) \
	(((t)->tv_sec >= 0) && (((unsigned long) (t)->tv_usec) < USEC_PER_SEC))

static int do_setitimer(int which, struct itimerspec64 *value,
			struct itimerspec64 *ovalue)
{
	struct task_struct *tsk = current;
	struct hrtimer *timer;
	ktime_t expires;

	switch (which) {
	case ITIMER_REAL:
again:
		spin_lock_irq(&tsk->sighand->siglock);
		timer = &tsk->signal->real_timer;
		if (ovalue) {
			ovalue->it_value = itimer_get_remtime(timer);
			ovalue->it_interval
				= ktime_to_timespec64(tsk->signal->it_real_incr);
		}
		/* We are sharing ->siglock with it_real_fn() */
		if (hrtimer_try_to_cancel(timer) < 0) {
			spin_unlock_irq(&tsk->sighand->siglock);
			hrtimer_cancel_wait_running(timer);
			goto again;
		}
		expires = timespec64_to_ktime(value->it_value);
		if (expires != 0) {
			tsk->signal->it_real_incr =
				timespec64_to_ktime(value->it_interval);
			hrtimer_start(timer, expires, HRTIMER_MODE_REL);
		} else
			tsk->signal->it_real_incr = 0;

		trace_itimer_state(ITIMER_REAL, value, 0);
		spin_unlock_irq(&tsk->sighand->siglock);
		break;
	case ITIMER_VIRTUAL:
		set_cpu_itimer(tsk, CPUCLOCK_VIRT, value, ovalue);
		break;
	case ITIMER_PROF:
		set_cpu_itimer(tsk, CPUCLOCK_PROF, value, ovalue);
		break;
	default:
		return -EINVAL;
	}
	return 0;
}

#ifdef CONFIG_SECURITY_SELINUX
void clear_itimer(void)
{
	struct itimerspec64 v = {};
	int i;

	for (i = 0; i < 3; i++)
		do_setitimer(i, &v, NULL);
}
#endif

#ifdef __ARCH_WANT_SYS_ALARM

/**
 * alarm_setitimer - set alarm in seconds
 *
 * @seconds:	number of seconds until alarm
 *		0 disables the alarm
 *
 * Returns the remaining time in seconds of a pending timer or 0 when
 * the timer is not active.
 *
 * On 32 bit machines the seconds value is limited to (INT_MAX/2) to avoid
 * negative timeval settings which would cause immediate expiry.
 */
static unsigned int alarm_setitimer(unsigned int seconds)
{
	struct itimerspec64 it_new, it_old;

#if BITS_PER_LONG < 64
	if (seconds > INT_MAX)
		seconds = INT_MAX;
#endif
	it_new.it_value.tv_sec = seconds;
	it_new.it_value.tv_nsec = 0;
	it_new.it_interval.tv_sec = it_new.it_interval.tv_nsec = 0;

	do_setitimer(ITIMER_REAL, &it_new, &it_old);

	/*
	 * We can't return 0 if we have an alarm pending ...  And we'd
	 * better return too much than too little anyway
	 */
	if ((!it_old.it_value.tv_sec && it_old.it_value.tv_nsec) ||
	      it_old.it_value.tv_nsec >= (NSEC_PER_SEC / 2))
		it_old.it_value.tv_sec++;

	return it_old.it_value.tv_sec;
}

/*
 * For backwards compatibility?  This can be done in libc so Alpha
 * and all newer ports shouldn't need it.
 */
SYSCALL_DEFINE1(alarm, unsigned int, seconds)
{
	return alarm_setitimer(seconds);
}

#endif

static int get_itimerval(struct itimerspec64 *o, const struct __kernel_old_itimerval __user *i)
{
	struct __kernel_old_itimerval v;

	if (copy_from_user(&v, i, sizeof(struct __kernel_old_itimerval)))
		return -EFAULT;

	/* Validate the timevals in value. */
	if (!timeval_valid(&v.it_value) ||
	    !timeval_valid(&v.it_interval))
		return -EINVAL;

	o->it_interval.tv_sec = v.it_interval.tv_sec;
	o->it_interval.tv_nsec = v.it_interval.tv_usec * NSEC_PER_USEC;
	o->it_value.tv_sec = v.it_value.tv_sec;
	o->it_value.tv_nsec = v.it_value.tv_usec * NSEC_PER_USEC;
	return 0;
}

SYSCALL_DEFINE3(setitimer, int, which, struct __kernel_old_itimerval __user *, value,
		struct __kernel_old_itimerval __user *, ovalue)
{
	struct itimerspec64 set_buffer, get_buffer;
	int error;

	if (value) {
		error = get_itimerval(&set_buffer, value);
		if (error)
			return error;
	} else {
		memset(&set_buffer, 0, sizeof(set_buffer));
		printk_once(KERN_WARNING "%s calls setitimer() with new_value NULL pointer."
			    " Misfeature support will be removed\n",
			    current->comm);
	}

	error = do_setitimer(which, &set_buffer, ovalue ? &get_buffer : NULL);
	if (error || !ovalue)
		return error;

	if (put_itimerval(ovalue, &get_buffer))
		return -EFAULT;
	return 0;
}

#if defined(CONFIG_COMPAT) || defined(CONFIG_ALPHA)
static int get_old_itimerval32(struct itimerspec64 *o, const struct old_itimerval32 __user *i)
{
	struct old_itimerval32 v32;

	if (copy_from_user(&v32, i, sizeof(struct old_itimerval32)))
		return -EFAULT;

	/* Validate the timevals in value.  */
	if (!timeval_valid(&v32.it_value) ||
	    !timeval_valid(&v32.it_interval))
		return -EINVAL;

	o->it_interval.tv_sec = v32.it_interval.tv_sec;
	o->it_interval.tv_nsec = v32.it_interval.tv_usec * NSEC_PER_USEC;
	o->it_value.tv_sec = v32.it_value.tv_sec;
	o->it_value.tv_nsec = v32.it_value.tv_usec * NSEC_PER_USEC;
	return 0;
}

COMPAT_SYSCALL_DEFINE3(setitimer, int, which,
		       struct old_itimerval32 __user *, value,
		       struct old_itimerval32 __user *, ovalue)
{
	struct itimerspec64 set_buffer, get_buffer;
	int error;

	if (value) {
		error = get_old_itimerval32(&set_buffer, value);
		if (error)
			return error;
	} else {
		memset(&set_buffer, 0, sizeof(set_buffer));
		printk_once(KERN_WARNING "%s calls setitimer() with new_value NULL pointer."
			    " Misfeature support will be removed\n",
			    current->comm);
	}

	error = do_setitimer(which, &set_buffer, ovalue ? &get_buffer : NULL);
	if (error || !ovalue)
		return error;
	if (put_old_itimerval32(ovalue, &get_buffer))
		return -EFAULT;
	return 0;
}
#endif