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Message-Id: <20220504224058.476193-9-ebiederm@xmission.com>
Date: Wed, 4 May 2022 17:40:56 -0500
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: linux-kernel@...r.kernel.org
Cc: rjw@...ysocki.net, Oleg Nesterov <oleg@...hat.com>,
mingo@...nel.org, vincent.guittot@...aro.org,
dietmar.eggemann@....com, rostedt@...dmis.org, mgorman@...e.de,
bigeasy@...utronix.de, Will Deacon <will@...nel.org>,
tj@...nel.org, linux-pm@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Richard Weinberger <richard@....at>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>,
Johannes Berg <johannes@...solutions.net>,
linux-um@...ts.infradead.org, Chris Zankel <chris@...kel.net>,
Max Filippov <jcmvbkbc@...il.com>,
linux-xtensa@...ux-xtensa.org, Kees Cook <keescook@...omium.org>,
Jann Horn <jannh@...gle.com>, linux-ia64@...r.kernel.org,
"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH v3 09/11] ptrace: Don't change __state
Stop playing with tsk->__state to remove TASK_WAKEKILL while a ptrace
command is executing.
Instead remove TASK_WAKEKILL from the definition of TASK_TRACED, and
implemention a new jobctl flag TASK_PTRACE_FROZEN. This new flag is
set in jobctl_freeze_task and cleared when ptrace_stop is awoken or in
jobctl_unfreeze_task (when ptrace_stop remains asleep).
In signal_wake_up add __TASK_TRACED to state along with TASK_WAKEKILL
when the wake up is for a fatal signal. Skip adding __TASK_TRACED
when TASK_PTRACE_FROZEN is not set. This has the same effect as
changing TASK_TRACED to __TASK_TRACED as all of the wake_ups that use
TASK_KILLABLE go through signal_wake_up.
Handle a ptrace_stop being called with a pending fatal signal.
Previously it would have been handled by schedule simply failing to
sleep. As TASK_WAKEKILL is no longer part of TASK_TRACED schedule
will sleep with a fatal_signal_pending. The code in signal_wake_up
guarantees that the code will be awaked by any fatal signal that
codes after TASK_TRACED is set.
Previously the __state value of __TASK_TRACED was changed to
TASK_RUNNING when woken up or back to TASK_TRACED when the code was
left in ptrace_stop. Now when woken up ptrace_stop now clears
JOBCTL_PTRACE_FROZEN and when left sleeping ptrace_unfreezed_traced
clears JOBCTL_PTRACE_FROZEN.
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
include/linux/sched.h | 2 +-
include/linux/sched/jobctl.h | 2 ++
include/linux/sched/signal.h | 5 +++--
kernel/ptrace.c | 21 ++++++++-------------
kernel/sched/core.c | 5 +----
kernel/signal.c | 10 +++++++---
6 files changed, 22 insertions(+), 23 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d5e3c00b74e1..610f2fdb1e2c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -103,7 +103,7 @@ struct task_group;
/* Convenience macros for the sake of set_current_state: */
#define TASK_KILLABLE (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
#define TASK_STOPPED (TASK_WAKEKILL | __TASK_STOPPED)
-#define TASK_TRACED (TASK_WAKEKILL | __TASK_TRACED)
+#define TASK_TRACED __TASK_TRACED
#define TASK_IDLE (TASK_UNINTERRUPTIBLE | TASK_NOLOAD)
diff --git a/include/linux/sched/jobctl.h b/include/linux/sched/jobctl.h
index fa067de9f1a9..d556c3425963 100644
--- a/include/linux/sched/jobctl.h
+++ b/include/linux/sched/jobctl.h
@@ -19,6 +19,7 @@ struct task_struct;
#define JOBCTL_TRAPPING_BIT 21 /* switching to TRACED */
#define JOBCTL_LISTENING_BIT 22 /* ptracer is listening for events */
#define JOBCTL_TRAP_FREEZE_BIT 23 /* trap for cgroup freezer */
+#define JOBCTL_PTRACE_FROZEN_BIT 24 /* frozen for ptrace */
#define JOBCTL_STOP_DEQUEUED (1UL << JOBCTL_STOP_DEQUEUED_BIT)
#define JOBCTL_STOP_PENDING (1UL << JOBCTL_STOP_PENDING_BIT)
@@ -28,6 +29,7 @@ struct task_struct;
#define JOBCTL_TRAPPING (1UL << JOBCTL_TRAPPING_BIT)
#define JOBCTL_LISTENING (1UL << JOBCTL_LISTENING_BIT)
#define JOBCTL_TRAP_FREEZE (1UL << JOBCTL_TRAP_FREEZE_BIT)
+#define JOBCTL_PTRACE_FROZEN (1UL << JOBCTL_PTRACE_FROZEN_BIT)
#define JOBCTL_TRAP_MASK (JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY)
#define JOBCTL_PENDING_MASK (JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK)
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 3c8b34876744..e66948abbee4 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -435,9 +435,10 @@ extern void calculate_sigpending(void);
extern void signal_wake_up_state(struct task_struct *t, unsigned int state);
-static inline void signal_wake_up(struct task_struct *t, bool resume)
+static inline void signal_wake_up(struct task_struct *t, bool fatal)
{
- signal_wake_up_state(t, resume ? TASK_WAKEKILL : 0);
+ fatal = fatal && !(t->jobctl & JOBCTL_PTRACE_FROZEN);
+ signal_wake_up_state(t, fatal ? TASK_WAKEKILL | __TASK_TRACED : 0);
}
static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume)
{
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 05953ac9f7bd..83ed28262708 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -197,7 +197,7 @@ static bool ptrace_freeze_traced(struct task_struct *task)
spin_lock_irq(&task->sighand->siglock);
if (task_is_traced(task) && !looks_like_a_spurious_pid(task) &&
!__fatal_signal_pending(task)) {
- WRITE_ONCE(task->__state, __TASK_TRACED);
+ task->jobctl |= JOBCTL_PTRACE_FROZEN;
ret = true;
}
spin_unlock_irq(&task->sighand->siglock);
@@ -207,23 +207,19 @@ static bool ptrace_freeze_traced(struct task_struct *task)
static void ptrace_unfreeze_traced(struct task_struct *task)
{
- if (READ_ONCE(task->__state) != __TASK_TRACED)
- return;
-
- WARN_ON(!task->ptrace || task->parent != current);
+ unsigned long flags;
/*
- * PTRACE_LISTEN can allow ptrace_trap_notify to wake us up remotely.
- * Recheck state under the lock to close this race.
+ * The child may be awake and may have cleared
+ * JOBCTL_PTRACE_FROZEN (see ptrace_resume). The child will
+ * not set JOBCTL_PTRACE_FROZEN or enter __TASK_TRACED anew.
*/
- spin_lock_irq(&task->sighand->siglock);
- if (READ_ONCE(task->__state) == __TASK_TRACED) {
+ if (lock_task_sighand(task, &flags)) {
+ task->jobctl &= ~JOBCTL_PTRACE_FROZEN;
if (__fatal_signal_pending(task))
wake_up_state(task, __TASK_TRACED);
- else
- WRITE_ONCE(task->__state, TASK_TRACED);
+ unlock_task_sighand(task, &flags);
}
- spin_unlock_irq(&task->sighand->siglock);
}
/**
@@ -256,7 +252,6 @@ static int ptrace_check_attach(struct task_struct *child, bool ignore_state)
*/
read_lock(&tasklist_lock);
if (child->ptrace && child->parent == current) {
- WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED);
/*
* child->sighand can't be NULL, release_task()
* does ptrace_unlink() before __exit_signal().
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d575b4914925..3c351707e830 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6304,10 +6304,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
/*
* We must load prev->state once (task_struct::state is volatile), such
- * that:
- *
- * - we form a control dependency vs deactivate_task() below.
- * - ptrace_{,un}freeze_traced() can change ->state underneath us.
+ * that we form a control dependency vs deactivate_task() below.
*/
prev_state = READ_ONCE(prev->__state);
if (!(sched_mode & SM_MASK_PREEMPT) && prev_state) {
diff --git a/kernel/signal.c b/kernel/signal.c
index 16828fde5424..e0b416b21ad3 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2210,9 +2210,13 @@ static int ptrace_stop(int exit_code, int why, unsigned long message,
}
/*
- * schedule() will not sleep if there is a pending signal that
- * can awaken the task.
+ * After this point signal_wake_up will clear TASK_TRACED
+ * if a fatal signal comes in. Handle previous fatal signals
+ * here to prevent ptrace_stop sleeping in schedule.
*/
+ if (__fatal_signal_pending(current))
+ return exit_code;
+
set_special_state(TASK_TRACED);
/*
@@ -2300,7 +2304,7 @@ static int ptrace_stop(int exit_code, int why, unsigned long message,
current->exit_code = 0;
/* LISTENING can be set only during STOP traps, clear it */
- current->jobctl &= ~JOBCTL_LISTENING;
+ current->jobctl &= ~(JOBCTL_LISTENING | JOBCTL_PTRACE_FROZEN);
/*
* Queued signals ignored us while we were stopped for tracing.
--
2.35.3
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