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sched,signal,ptrace: Rework TASK_TRACED, TASK_STOPPED state

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Currently ptrace_stop() / do_signal_stop() rely on the special states
TASK_TRACED and TASK_STOPPED resp. to keep unique state. That is, this
state exists only in task->__state and nowhere else.

There's two spots of bother with this:

 - PREEMPT_RT has task->saved_state which complicates matters,
   meaning task_is_{traced,stopped}() needs to check an additional
   variable.

 - An alternative freezer implementation that itself relies on a
   special TASK state would loose TASK_TRACED/TASK_STOPPED and will
   result in misbehaviour.

As such, add additional state to task->jobctl to track this state
outside of task->__state.

NOTE: this doesn't actually fix anything yet, just adds extra state.

--EWB
  * didn't add a unnecessary newline in signal.h
  * Update t->jobctl in signal_wake_up and ptrace_signal_wake_up
    instead of in signal_wake_up_state.  This prevents the clearing
    of TASK_STOPPED and TASK_TRACED from getting lost.
  * Added warnings if JOBCTL_STOPPED or JOBCTL_TRACED are not cleared

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220421150654.757693825@infradead.org
Tested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lkml.kernel.org/r/20220505182645.497868-12-ebiederm@xmission.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Peter Zijlstra 2022-05-03 15:57:47 -05:00 committed by Eric W. Biederman
parent 5b4197cb28
commit 31cae1eaae
5 changed files with 45 additions and 14 deletions
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8
include/linux/sched.h
View File

@ -118,11 +118,9 @@ struct task_group;
#define task_is_running(task) (READ_ONCE((task)->__state) == TASK_RUNNING)
#define task_is_traced(task) ((READ_ONCE(task->__state) & __TASK_TRACED) != 0)
#define task_is_stopped(task) ((READ_ONCE(task->__state) & __TASK_STOPPED) != 0)
#define task_is_stopped_or_traced(task) ((READ_ONCE(task->__state) & (__TASK_STOPPED | __TASK_TRACED)) != 0)
#define task_is_traced(task) ((READ_ONCE(task->jobctl) & JOBCTL_TRACED) != 0)
#define task_is_stopped(task) ((READ_ONCE(task->jobctl) & JOBCTL_STOPPED) != 0)
#define task_is_stopped_or_traced(task) ((READ_ONCE(task->jobctl) & (JOBCTL_STOPPED | JOBCTL_TRACED)) != 0)
/*
* Special states are those that do not use the normal wait-loop pattern. See

6
include/linux/sched/jobctl.h
View File

@ -21,6 +21,9 @@ struct task_struct;
#define JOBCTL_TRAP_FREEZE_BIT 23 /* trap for cgroup freezer */
#define JOBCTL_PTRACE_FROZEN_BIT 24 /* frozen for ptrace */
#define JOBCTL_STOPPED_BIT 26 /* do_signal_stop() */
#define JOBCTL_TRACED_BIT 27 /* ptrace_stop() */
#define JOBCTL_STOP_DEQUEUED (1UL << JOBCTL_STOP_DEQUEUED_BIT)
#define JOBCTL_STOP_PENDING (1UL << JOBCTL_STOP_PENDING_BIT)
#define JOBCTL_STOP_CONSUME (1UL << JOBCTL_STOP_CONSUME_BIT)
@ -31,6 +34,9 @@ struct task_struct;
#define JOBCTL_TRAP_FREEZE (1UL << JOBCTL_TRAP_FREEZE_BIT)
#define JOBCTL_PTRACE_FROZEN (1UL << JOBCTL_PTRACE_FROZEN_BIT)
#define JOBCTL_STOPPED (1UL << JOBCTL_STOPPED_BIT)
#define JOBCTL_TRACED (1UL << JOBCTL_TRACED_BIT)
#define JOBCTL_TRAP_MASK (JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY)
#define JOBCTL_PENDING_MASK (JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK)

19
include/linux/sched/signal.h
View File

@ -294,8 +294,10 @@ static inline int kernel_dequeue_signal(void)
static inline void kernel_signal_stop(void)
{
spin_lock_irq(&current->sighand->siglock);
if (current->jobctl & JOBCTL_STOP_DEQUEUED)
if (current->jobctl & JOBCTL_STOP_DEQUEUED) {
current->jobctl |= JOBCTL_STOPPED;
set_special_state(TASK_STOPPED);
}
spin_unlock_irq(&current->sighand->siglock);
schedule();
@ -437,12 +439,21 @@ extern void signal_wake_up_state(struct task_struct *t, unsigned int state);
static inline void signal_wake_up(struct task_struct *t, bool fatal)
{
fatal = fatal && !(t->jobctl & JOBCTL_PTRACE_FROZEN);
signal_wake_up_state(t, fatal ? TASK_WAKEKILL | __TASK_TRACED : 0);
unsigned int state = 0;
if (fatal && !(t->jobctl & JOBCTL_PTRACE_FROZEN)) {
t->jobctl &= ~(JOBCTL_STOPPED | JOBCTL_TRACED);
state = TASK_WAKEKILL | __TASK_TRACED;
}
signal_wake_up_state(t, state);
}
static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume)
{
signal_wake_up_state(t, resume ? __TASK_TRACED : 0);
unsigned int state = 0;
if (resume) {
t->jobctl &= ~JOBCTL_TRACED;
state = __TASK_TRACED;
}
signal_wake_up_state(t, state);
}
void task_join_group_stop(struct task_struct *task);

16
kernel/ptrace.c
View File

@ -185,7 +185,12 @@ static bool looks_like_a_spurious_pid(struct task_struct *task)
return true;
}
/* Ensure that nothing can wake it up, even SIGKILL */
/*
* Ensure that nothing can wake it up, even SIGKILL
*
* A task is switched to this state while a ptrace operation is in progress;
* such that the ptrace operation is uninterruptible.
*/
static bool ptrace_freeze_traced(struct task_struct *task)
{
bool ret = false;
@ -216,8 +221,10 @@ static void ptrace_unfreeze_traced(struct task_struct *task)
*/
if (lock_task_sighand(task, &flags)) {
task->jobctl &= ~JOBCTL_PTRACE_FROZEN;
if (__fatal_signal_pending(task))
if (__fatal_signal_pending(task)) {
task->jobctl &= ~TASK_TRACED;
wake_up_state(task, __TASK_TRACED);
}
unlock_task_sighand(task, &flags);
}
}
@ -462,8 +469,10 @@ static int ptrace_attach(struct task_struct *task, long request,
* in and out of STOPPED are protected by siglock.
*/
if (task_is_stopped(task) &&
task_set_jobctl_pending(task, JOBCTL_TRAP_STOP | JOBCTL_TRAPPING))
task_set_jobctl_pending(task, JOBCTL_TRAP_STOP | JOBCTL_TRAPPING)) {
task->jobctl &= ~JOBCTL_STOPPED;
signal_wake_up_state(task, __TASK_STOPPED);
}
spin_unlock(&task->sighand->siglock);
@ -875,6 +884,7 @@ static int ptrace_resume(struct task_struct *child, long request,
*/
spin_lock_irq(&child->sighand->siglock);
child->exit_code = data;
child->jobctl &= ~JOBCTL_TRACED;
wake_up_state(child, __TASK_TRACED);
spin_unlock_irq(&child->sighand->siglock);

10
kernel/signal.c
View File

@ -762,7 +762,10 @@ still_pending:
*/
void signal_wake_up_state(struct task_struct *t, unsigned int state)
{
lockdep_assert_held(&t->sighand->siglock);
set_tsk_thread_flag(t, TIF_SIGPENDING);
/*
* TASK_WAKEKILL also means wake it up in the stopped/traced/killable
* case. We don't check t->state here because there is a race with it
@ -930,9 +933,10 @@ static bool prepare_signal(int sig, struct task_struct *p, bool force)
for_each_thread(p, t) {
flush_sigqueue_mask(&flush, &t->pending);
task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING);
if (likely(!(t->ptrace & PT_SEIZED)))
if (likely(!(t->ptrace & PT_SEIZED))) {
t->jobctl &= ~JOBCTL_STOPPED;
wake_up_state(t, __TASK_STOPPED);
else
} else
ptrace_trap_notify(t);
}
@ -2218,6 +2222,7 @@ static int ptrace_stop(int exit_code, int why, unsigned long message,
return exit_code;
set_special_state(TASK_TRACED);
current->jobctl |= JOBCTL_TRACED;
/*
* We're committing to trapping. TRACED should be visible before
@ -2436,6 +2441,7 @@ static bool do_signal_stop(int signr)
if (task_participate_group_stop(current))
notify = CLD_STOPPED;
current->jobctl |= JOBCTL_STOPPED;
set_special_state(TASK_STOPPED);
spin_unlock_irq(&current->sighand->siglock);