ptrace: implement PTRACE_LISTEN
The previous patch implemented async notification for ptrace but it
only worked while trace is running. This patch introduces
PTRACE_LISTEN which is suggested by Oleg Nestrov.
It's allowed iff tracee is in STOP trap and puts tracee into
quasi-running state - tracee never really runs but wait(2) and
ptrace(2) consider it to be running. While ptracer is listening,
tracee is allowed to re-enter STOP to notify an async event.
Listening state is cleared on the first notification. Ptracer can
also clear it by issuing INTERRUPT - tracee will re-trap into STOP
with listening state cleared.
This allows ptracer to monitor group stop state without running tracee
- use INTERRUPT to put tracee into STOP trap, issue LISTEN and then
wait(2) to wait for the next group stop event. When it happens,
PTRACE_GETSIGINFO provides information to determine the current state.
Test program follows.
#define PTRACE_SEIZE 0x4206
#define PTRACE_INTERRUPT 0x4207
#define PTRACE_LISTEN 0x4208
#define PTRACE_SEIZE_DEVEL 0x80000000
static const struct timespec ts1s = { .tv_sec = 1 };
int main(int argc, char **argv)
{
pid_t tracee, tracer;
int i;
tracee = fork();
if (!tracee)
while (1)
pause();
tracer = fork();
if (!tracer) {
siginfo_t si;
ptrace(PTRACE_SEIZE, tracee, NULL,
(void *)(unsigned long)PTRACE_SEIZE_DEVEL);
ptrace(PTRACE_INTERRUPT, tracee, NULL, NULL);
repeat:
waitid(P_PID, tracee, NULL, WSTOPPED);
ptrace(PTRACE_GETSIGINFO, tracee, NULL, &si);
if (!si.si_code) {
printf("tracer: SIG %d\n", si.si_signo);
ptrace(PTRACE_CONT, tracee, NULL,
(void *)(unsigned long)si.si_signo);
goto repeat;
}
printf("tracer: stopped=%d signo=%d\n",
si.si_signo != SIGTRAP, si.si_signo);
if (si.si_signo != SIGTRAP)
ptrace(PTRACE_LISTEN, tracee, NULL, NULL);
else
ptrace(PTRACE_CONT, tracee, NULL, NULL);
goto repeat;
}
for (i = 0; i < 3; i++) {
nanosleep(&ts1s, NULL);
printf("mother: SIGSTOP\n");
kill(tracee, SIGSTOP);
nanosleep(&ts1s, NULL);
printf("mother: SIGCONT\n");
kill(tracee, SIGCONT);
}
nanosleep(&ts1s, NULL);
kill(tracer, SIGKILL);
kill(tracee, SIGKILL);
return 0;
}
This is identical to the program to test TRAP_NOTIFY except that
tracee is PTRACE_LISTEN'd instead of PTRACE_CONT'd when group stopped.
This allows ptracer to monitor when group stop ends without running
tracee.
# ./test-listen
tracer: stopped=0 signo=5
mother: SIGSTOP
tracer: SIG 19
tracer: stopped=1 signo=19
mother: SIGCONT
tracer: stopped=0 signo=5
tracer: SIG 18
mother: SIGSTOP
tracer: SIG 19
tracer: stopped=1 signo=19
mother: SIGCONT
tracer: stopped=0 signo=5
tracer: SIG 18
mother: SIGSTOP
tracer: SIG 19
tracer: stopped=1 signo=19
mother: SIGCONT
tracer: stopped=0 signo=5
tracer: SIG 18
-v2: Moved JOBCTL_LISTENING check in wait_task_stopped() into
task_stopped_code() as suggested by Oleg.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
This commit is contained in:
Tejun Heo
Oleg Nesterov
parent
fb1d910c17
commit
544b2c91a9
5 changed files with 53 additions and 8 deletions
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@ -49,6 +49,7 @@
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#define PTRACE_SEIZE 0x4206
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#define PTRACE_INTERRUPT 0x4207
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#define PTRACE_LISTEN 0x4208
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/* flags in @data for PTRACE_SEIZE */
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#define PTRACE_SEIZE_DEVEL 0x80000000 /* temp flag for development */
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@ -1813,6 +1813,7 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
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#define JOBCTL_TRAP_STOP_BIT 19 /* trap for STOP */
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#define JOBCTL_TRAP_NOTIFY_BIT 20 /* trap for NOTIFY */
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#define JOBCTL_TRAPPING_BIT 21 /* switching to TRACED */
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#define JOBCTL_LISTENING_BIT 22 /* ptracer is listening for events */
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#define JOBCTL_STOP_DEQUEUED (1 << JOBCTL_STOP_DEQUEUED_BIT)
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#define JOBCTL_STOP_PENDING (1 << JOBCTL_STOP_PENDING_BIT)
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@ -1820,6 +1821,7 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
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#define JOBCTL_TRAP_STOP (1 << JOBCTL_TRAP_STOP_BIT)
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#define JOBCTL_TRAP_NOTIFY (1 << JOBCTL_TRAP_NOTIFY_BIT)
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#define JOBCTL_TRAPPING (1 << JOBCTL_TRAPPING_BIT)
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#define JOBCTL_LISTENING (1 << JOBCTL_LISTENING_BIT)
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#define JOBCTL_TRAP_MASK (JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY)
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#define JOBCTL_PENDING_MASK (JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK)
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@ -1368,7 +1368,8 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
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static int *task_stopped_code(struct task_struct *p, bool ptrace)
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{
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if (ptrace) {
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if (task_is_stopped_or_traced(p))
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if (task_is_stopped_or_traced(p) &&
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!(p->jobctl & JOBCTL_LISTENING))
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return &p->exit_code;
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} else {
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if (p->signal->flags & SIGNAL_STOP_STOPPED)
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@ -146,7 +146,8 @@ int ptrace_check_attach(struct task_struct *child, bool ignore_state)
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*/
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spin_lock_irq(&child->sighand->siglock);
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WARN_ON_ONCE(task_is_stopped(child));
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if (task_is_traced(child) || ignore_state)
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if (ignore_state || (task_is_traced(child) &&
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!(child->jobctl & JOBCTL_LISTENING)))
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ret = 0;
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spin_unlock_irq(&child->sighand->siglock);
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}
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@ -660,7 +661,7 @@ int ptrace_request(struct task_struct *child, long request,
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{
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bool seized = child->ptrace & PT_SEIZED;
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int ret = -EIO;
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siginfo_t siginfo;
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siginfo_t siginfo, *si;
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void __user *datavp = (void __user *) data;
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unsigned long __user *datalp = datavp;
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unsigned long flags;
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@ -710,8 +711,43 @@ int ptrace_request(struct task_struct *child, long request,
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if (unlikely(!seized || !lock_task_sighand(child, &flags)))
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break;
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/*
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* INTERRUPT doesn't disturb existing trap sans one
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* exception. If ptracer issued LISTEN for the current
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* STOP, this INTERRUPT should clear LISTEN and re-trap
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* tracee into STOP.
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*/
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if (likely(task_set_jobctl_pending(child, JOBCTL_TRAP_STOP)))
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signal_wake_up(child, 0);
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signal_wake_up(child, child->jobctl & JOBCTL_LISTENING);
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unlock_task_sighand(child, &flags);
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ret = 0;
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break;
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case PTRACE_LISTEN:
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/*
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* Listen for events. Tracee must be in STOP. It's not
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* resumed per-se but is not considered to be in TRACED by
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* wait(2) or ptrace(2). If an async event (e.g. group
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* stop state change) happens, tracee will enter STOP trap
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* again. Alternatively, ptracer can issue INTERRUPT to
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* finish listening and re-trap tracee into STOP.
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*/
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if (unlikely(!seized || !lock_task_sighand(child, &flags)))
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break;
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si = child->last_siginfo;
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if (unlikely(!si || si->si_code >> 8 != PTRACE_EVENT_STOP))
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break;
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child->jobctl |= JOBCTL_LISTENING;
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/*
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* If NOTIFY is set, it means event happened between start
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* of this trap and now. Trigger re-trap immediately.
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*/
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if (child->jobctl & JOBCTL_TRAP_NOTIFY)
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signal_wake_up(child, true);
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unlock_task_sighand(child, &flags);
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ret = 0;
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@ -825,9 +825,11 @@ static int check_kill_permission(int sig, struct siginfo *info,
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* TRAP_STOP to notify ptracer of an event. @t must have been seized by
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* ptracer.
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*
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* If @t is running, STOP trap will be taken. If already trapped, STOP
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* trap will be eventually taken without returning to userland after the
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* existing traps are finished by PTRACE_CONT.
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* If @t is running, STOP trap will be taken. If trapped for STOP and
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* ptracer is listening for events, tracee is woken up so that it can
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* re-trap for the new event. If trapped otherwise, STOP trap will be
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* eventually taken without returning to userland after the existing traps
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* are finished by PTRACE_CONT.
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*
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* CONTEXT:
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* Must be called with @task->sighand->siglock held.
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@ -838,7 +840,7 @@ static void ptrace_trap_notify(struct task_struct *t)
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assert_spin_locked(&t->sighand->siglock);
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task_set_jobctl_pending(t, JOBCTL_TRAP_NOTIFY);
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signal_wake_up(t, 0);
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signal_wake_up(t, t->jobctl & JOBCTL_LISTENING);
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}
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/*
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@ -1894,6 +1896,9 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
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spin_lock_irq(¤t->sighand->siglock);
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current->last_siginfo = NULL;
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/* LISTENING can be set only during STOP traps, clear it */
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current->jobctl &= ~JOBCTL_LISTENING;
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/*
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* Queued signals ignored us while we were stopped for tracing.
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* So check for any that we should take before resuming user mode.
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