[PATCH v4 6/6] posix-timers: make it configurable

From: Nicolas Pitre
Date: Fri Nov 11 2016 - 00:11:34 EST

Some embedded systems have no use for them. This removes about
25KB from the kernel binary size when configured out.

Corresponding syscalls are routed to a stub logging the attempt to
use those syscalls which should be enough of a clue if they were
disabled without proper consideration. They are: timer_create,
timer_gettime: timer_getoverrun, timer_settime, timer_delete,
clock_adjtime, setitimer, getitimer, alarm.

The clock_settime, clock_gettime, clock_getres and clock_nanosleep
syscalls are replaced by simple wrappers compatible with CLOCK_REALTIME,
CLOCK_MONOTONIC and CLOCK_BOOTTIME only which should cover the vast
majority of use cases with very little code.

Signed-off-by: Nicolas Pitre <nico@xxxxxxxxxx>
Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Acked-by: Richard Cochran <richardcochran@xxxxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
arch/alpha/kernel/osf_sys.c | 8 +++
drivers/char/Kconfig | 1 +
drivers/ptp/Kconfig | 2 +-
fs/exec.c | 2 +
init/Kconfig | 17 ++++++
kernel/compat.c | 8 +++
kernel/exit.c | 11 +++-
kernel/fork.c | 2 +
kernel/signal.c | 6 +++
kernel/sys.c | 3 +-
kernel/time/Makefile | 10 +++-
kernel/time/alarmtimer.c | 6 ++-
kernel/time/posix-stubs.c | 123 ++++++++++++++++++++++++++++++++++++++++++++
kernel/time/timer.c | 3 +-
security/selinux/hooks.c | 11 ++--
15 files changed, 200 insertions(+), 13 deletions(-)
create mode 100644 kernel/time/posix-stubs.c

diff --git a/arch/alpha/kernel/osf_sys.c b/arch/alpha/kernel/osf_sys.c
index ffb93f499c..56e427c7aa 100644
--- a/arch/alpha/kernel/osf_sys.c
+++ b/arch/alpha/kernel/osf_sys.c
@@ -1029,11 +1029,16 @@ SYSCALL_DEFINE2(osf_settimeofday, struct timeval32 __user *, tv,
return do_sys_settimeofday(tv ? &kts : NULL, tz ? &ktz : NULL);
}

+asmlinkage long sys_ni_posix_timers(void);
+
SYSCALL_DEFINE2(osf_getitimer, int, which, struct itimerval32 __user *, it)
{
struct itimerval kit;
int error;

+ if (!IS_ENABLED(CONFIG_POSIX_TIMERS))
+ return sys_ni_posix_timers();
+
error = do_getitimer(which, &kit);
if (!error && put_it32(it, &kit))
error = -EFAULT;
@@ -1047,6 +1052,9 @@ SYSCALL_DEFINE3(osf_setitimer, int, which, struct itimerval32 __user *, in,
struct itimerval kin, kout;
int error;

+ if (!IS_ENABLED(CONFIG_POSIX_TIMERS))
+ return sys_ni_posix_timers();
+
if (in) {
if (get_it32(&kin, in))
return -EFAULT;
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index dcc09739a5..45ba878ae0 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -542,6 +542,7 @@ config HANGCHECK_TIMER
config MMTIMER
tristate "MMTIMER Memory mapped RTC for SGI Altix"
depends on IA64_GENERIC || IA64_SGI_SN2
+ depends on POSIX_TIMERS
default y
help
The mmtimer device allows direct userspace access to the
diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig
index 0f7492f8ea..bdce332911 100644
--- a/drivers/ptp/Kconfig
+++ b/drivers/ptp/Kconfig
@@ -6,7 +6,7 @@ menu "PTP clock support"

config PTP_1588_CLOCK
tristate "PTP clock support"
- depends on NET
+ depends on NET && POSIX_TIMERS
select PPS
select NET_PTP_CLASSIFY
help
diff --git a/fs/exec.c b/fs/exec.c
index 6fcfb3f7b1..a67a172332 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1164,8 +1164,10 @@ static int de_thread(struct task_struct *tsk)
/* we have changed execution domain */
tsk->exit_signal = SIGCHLD;

+#ifdef CONFIG_POSIX_TIMERS
exit_itimers(sig);
flush_itimer_signals();
+#endif

if (atomic_read(&oldsighand->count) != 1) {
struct sighand_struct *newsighand;
diff --git a/init/Kconfig b/init/Kconfig
index 34407f15e6..456e0b8912 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1445,6 +1445,23 @@ config SYSCTL_SYSCALL

If unsure say N here.

+config POSIX_TIMERS
+ bool "Posix Clocks & timers" if EXPERT
+ default y
+ help
+ This includes native support for POSIX timers to the kernel.
+ Some embedded systems have no use for them and therefore they
+ can be configured out to reduce the size of the kernel image.
+
+ When this option is disabled, the following syscalls won't be
+ available: timer_create, timer_gettime: timer_getoverrun,
+ timer_settime, timer_delete, clock_adjtime, getitimer,
+ setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
+ clock_getres and clock_nanosleep syscalls will be limited to
+ CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
+
+ If unsure say y.
+
config KALLSYMS
bool "Load all symbols for debugging/ksymoops" if EXPERT
default y
diff --git a/kernel/compat.c b/kernel/compat.c
index 333d364be2..b3a047f208 100644
--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -307,12 +307,17 @@ static inline long put_compat_itimerval(struct compat_itimerval __user *o,
__put_user(i->it_value.tv_usec, &o->it_value.tv_usec)));
}

+asmlinkage long sys_ni_posix_timers(void);
+
COMPAT_SYSCALL_DEFINE2(getitimer, int, which,
struct compat_itimerval __user *, it)
{
struct itimerval kit;
int error;

+ if (!IS_ENABLED(CONFIG_POSIX_TIMERS))
+ return sys_ni_posix_timers();
+
error = do_getitimer(which, &kit);
if (!error && put_compat_itimerval(it, &kit))
error = -EFAULT;
@@ -326,6 +331,9 @@ COMPAT_SYSCALL_DEFINE3(setitimer, int, which,
struct itimerval kin, kout;
int error;

+ if (!IS_ENABLED(CONFIG_POSIX_TIMERS))
+ return sys_ni_posix_timers();
+
if (in) {
if (get_compat_itimerval(&kin, in))
return -EFAULT;
diff --git a/kernel/exit.c b/kernel/exit.c
index d16bcdd89d..684de019b6 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -92,11 +92,10 @@ static void __exit_signal(struct task_struct *tsk)
lockdep_tasklist_lock_is_held());
spin_lock(&sighand->siglock);

+#ifdef CONFIG_POSIX_TIMERS
posix_cpu_timers_exit(tsk);
if (group_dead) {
posix_cpu_timers_exit_group(tsk);
- tty = sig->tty;
- sig->tty = NULL;
} else {
/*
* This can only happen if the caller is de_thread().
@@ -105,7 +104,13 @@ static void __exit_signal(struct task_struct *tsk)
*/
if (unlikely(has_group_leader_pid(tsk)))
posix_cpu_timers_exit_group(tsk);
+ }
+#endif

+ if (group_dead) {
+ tty = sig->tty;
+ sig->tty = NULL;
+ } else {
/*
* If there is any task waiting for the group exit
* then notify it:
@@ -803,8 +808,10 @@ void __noreturn do_exit(long code)
acct_update_integrals(tsk);
group_dead = atomic_dec_and_test(&tsk->signal->live);
if (group_dead) {
+#ifdef CONFIG_POSIX_TIMERS
hrtimer_cancel(&tsk->signal->real_timer);
exit_itimers(tsk->signal);
+#endif
if (tsk->mm)
setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm);
}
diff --git a/kernel/fork.c b/kernel/fork.c
index 623259fc79..17da35fa77 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1342,8 +1342,10 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
seqlock_init(&sig->stats_lock);
prev_cputime_init(&sig->prev_cputime);

+#ifdef CONFIG_POSIX_TIMERS
hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
sig->real_timer.function = it_real_fn;
+#endif

task_lock(current->group_leader);
memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
diff --git a/kernel/signal.c b/kernel/signal.c
index 75761acc77..29a410780a 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -427,6 +427,7 @@ void flush_signals(struct task_struct *t)
spin_unlock_irqrestore(&t->sighand->siglock, flags);
}

+#ifdef CONFIG_POSIX_TIMERS
static void __flush_itimer_signals(struct sigpending *pending)
{
sigset_t signal, retain;
@@ -460,6 +461,7 @@ void flush_itimer_signals(void)
__flush_itimer_signals(&tsk->signal->shared_pending);
spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
}
+#endif

void ignore_signals(struct task_struct *t)
{
@@ -567,6 +569,7 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
if (!signr) {
signr = __dequeue_signal(&tsk->signal->shared_pending,
mask, info);
+#ifdef CONFIG_POSIX_TIMERS
/*
* itimer signal ?
*
@@ -590,6 +593,7 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
hrtimer_restart(tmr);
}
}
+#endif
}

recalc_sigpending();
@@ -611,6 +615,7 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
*/
current->jobctl |= JOBCTL_STOP_DEQUEUED;
}
+#ifdef CONFIG_POSIX_TIMERS
if ((info->si_code & __SI_MASK) == __SI_TIMER && info->si_sys_private) {
/*
* Release the siglock to ensure proper locking order
@@ -622,6 +627,7 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
do_schedule_next_timer(info);
spin_lock(&tsk->sighand->siglock);
}
+#endif
return signr;
}

diff --git a/kernel/sys.c b/kernel/sys.c
index 89d5be4181..78c9fb7dd6 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1416,7 +1416,8 @@ int do_prlimit(struct task_struct *tsk, unsigned int resource,
* applications, so we live with it
*/
if (!retval && new_rlim && resource == RLIMIT_CPU &&
- new_rlim->rlim_cur != RLIM_INFINITY)
+ new_rlim->rlim_cur != RLIM_INFINITY &&
+ IS_ENABLED(CONFIG_POSIX_TIMERS))
update_rlimit_cpu(tsk, new_rlim->rlim_cur);
out:
read_unlock(&tasklist_lock);
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index 49eca0beed..976840d29a 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -1,6 +1,12 @@
-obj-y += time.o timer.o hrtimer.o itimer.o posix-timers.o posix-cpu-timers.o
+obj-y += time.o timer.o hrtimer.o
obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o
-obj-y += timeconv.o timecounter.o posix-clock.o alarmtimer.o
+obj-y += timeconv.o timecounter.o alarmtimer.o
+
+ifeq ($(CONFIG_POSIX_TIMERS),y)
+ obj-y += posix-timers.o posix-cpu-timers.o posix-clock.o itimer.o
+else
+ obj-y += posix-stubs.o
+endif

obj-$(CONFIG_GENERIC_CLOCKEVENTS) += clockevents.o tick-common.o
ifeq ($(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST),y)
diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index c3aad685bb..9a878eacf9 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -848,8 +848,10 @@ static int __init alarmtimer_init(void)

alarmtimer_rtc_timer_init();

- posix_timers_register_clock(CLOCK_REALTIME_ALARM, &alarm_clock);
- posix_timers_register_clock(CLOCK_BOOTTIME_ALARM, &alarm_clock);
+ if (IS_ENABLED(CONFIG_POSIX_TIMERS)) {
+ posix_timers_register_clock(CLOCK_REALTIME_ALARM, &alarm_clock);
+ posix_timers_register_clock(CLOCK_BOOTTIME_ALARM, &alarm_clock);
+ }

/* Initialize alarm bases */
alarm_bases[ALARM_REALTIME].base_clockid = CLOCK_REALTIME;
diff --git a/kernel/time/posix-stubs.c b/kernel/time/posix-stubs.c
new file mode 100644
index 0000000000..cd6716e115
--- /dev/null
+++ b/kernel/time/posix-stubs.c
@@ -0,0 +1,123 @@
+/*
+ * Dummy stubs used when CONFIG_POSIX_TIMERS=n
+ *
+ * Created by: Nicolas Pitre, July 2016
+ * Copyright: (C) 2016 Linaro Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/linkage.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/errno.h>
+#include <linux/syscalls.h>
+#include <linux/ktime.h>
+#include <linux/timekeeping.h>
+#include <linux/posix-timers.h>
+
+asmlinkage long sys_ni_posix_timers(void)
+{
+ pr_err_once("process %d (%s) attempted a POSIX timer syscall "
+ "while CONFIG_POSIX_TIMERS is not set\n",
+ current->pid, current->comm);
+ return -ENOSYS;
+}
+
+#define SYS_NI(name) SYSCALL_ALIAS(sys_##name, sys_ni_posix_timers)
+
+SYS_NI(timer_create);
+SYS_NI(timer_gettime);
+SYS_NI(timer_getoverrun);
+SYS_NI(timer_settime);
+SYS_NI(timer_delete);
+SYS_NI(clock_adjtime);
+SYS_NI(getitimer);
+SYS_NI(setitimer);
+#ifdef __ARCH_WANT_SYS_ALARM
+SYS_NI(alarm);
+#endif
+
+/*
+ * We preserve minimal support for CLOCK_REALTIME and CLOCK_MONOTONIC
+ * as it is easy to remain compatible with little code. CLOCK_BOOTTIME
+ * is also included for convenience as at least systemd uses it.
+ */
+
+SYSCALL_DEFINE2(clock_settime, const clockid_t, which_clock,
+ const struct timespec __user *, tp)
+{
+ struct timespec new_tp;
+
+ if (which_clock != CLOCK_REALTIME)
+ return -EINVAL;
+ if (copy_from_user(&new_tp, tp, sizeof (*tp)))
+ return -EFAULT;
+ return do_sys_settimeofday(&new_tp, NULL);
+}
+
+SYSCALL_DEFINE2(clock_gettime, const clockid_t, which_clock,
+ struct timespec __user *,tp)
+{
+ struct timespec kernel_tp;
+
+ switch (which_clock) {
+ case CLOCK_REALTIME: ktime_get_real_ts(&kernel_tp); break;
+ case CLOCK_MONOTONIC: ktime_get_ts(&kernel_tp); break;
+ case CLOCK_BOOTTIME: get_monotonic_boottime(&kernel_tp); break;
+ default: return -EINVAL;
+ }
+ if (copy_to_user(tp, &kernel_tp, sizeof (kernel_tp)))
+ return -EFAULT;
+ return 0;
+}
+
+SYSCALL_DEFINE2(clock_getres, const clockid_t, which_clock, struct timespec __user *, tp)
+{
+ struct timespec rtn_tp = {
+ .tv_sec = 0,
+ .tv_nsec = hrtimer_resolution,
+ };
+
+ switch (which_clock) {
+ case CLOCK_REALTIME:
+ case CLOCK_MONOTONIC:
+ case CLOCK_BOOTTIME:
+ if (copy_to_user(tp, &rtn_tp, sizeof(rtn_tp)))
+ return -EFAULT;
+ return 0;
+ default:
+ return -EINVAL;
+ }
+}
+
+SYSCALL_DEFINE4(clock_nanosleep, const clockid_t, which_clock, int, flags,
+ const struct timespec __user *, rqtp,
+ struct timespec __user *, rmtp)
+{
+ struct timespec t;
+
+ switch (which_clock) {
+ case CLOCK_REALTIME:
+ case CLOCK_MONOTONIC:
+ case CLOCK_BOOTTIME:
+ if (copy_from_user(&t, rqtp, sizeof (struct timespec)))
+ return -EFAULT;
+ if (!timespec_valid(&t))
+ return -EINVAL;
+ return hrtimer_nanosleep(&t, rmtp, flags & TIMER_ABSTIME ?
+ HRTIMER_MODE_ABS : HRTIMER_MODE_REL,
+ which_clock);
+ default:
+ return -EINVAL;
+ }
+}
+
+#ifdef CONFIG_COMPAT
+long clock_nanosleep_restart(struct restart_block *restart_block)
+{
+ return hrtimer_nanosleep_restart(restart_block);
+}
+#endif
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 3ed6c67e17..099e43311f 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1601,7 +1601,8 @@ void update_process_times(int user_tick)
irq_work_tick();
#endif
scheduler_tick();
- run_posix_cpu_timers(p);
+ if (IS_ENABLED(CONFIG_POSIX_TIMERS))
+ run_posix_cpu_timers(p);
}

/**
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 0850579362..d769a136ea 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2525,7 +2525,8 @@ static void selinux_bprm_committing_creds(struct linux_binprm *bprm)
rlim->rlim_cur = min(rlim->rlim_max, initrlim->rlim_cur);
}
task_unlock(current);
- update_rlimit_cpu(current, rlimit(RLIMIT_CPU));
+ if (IS_ENABLED(CONFIG_POSIX_TIMERS))
+ update_rlimit_cpu(current, rlimit(RLIMIT_CPU));
}
}

@@ -2555,9 +2556,11 @@ static void selinux_bprm_committed_creds(struct linux_binprm *bprm)
*/
rc = avc_has_perm(osid, sid, SECCLASS_PROCESS, PROCESS__SIGINH, NULL);
if (rc) {
- memset(&itimer, 0, sizeof itimer);
- for (i = 0; i < 3; i++)
- do_setitimer(i, &itimer, NULL);
+ if (IS_ENABLED(CONFIG_POSIX_TIMERS)) {
+ memset(&itimer, 0, sizeof itimer);
+ for (i = 0; i < 3; i++)
+ do_setitimer(i, &itimer, NULL);
+ }
spin_lock_irq(&current->sighand->siglock);
if (!fatal_signal_pending(current)) {
flush_sigqueue(&current->pending);
--
2.7.4