[PATCH v3 4/6] ptrace: Track __TASK_TRACED state in p->ptrace

Peter Zijlstra
2021-10-09T10:20:34Z

Just like we can recover __TASK_STOPPED from p->jobctl, add some bits
to p->ptrace such that we can recover __TASK_TRACED.

All these t->ptrace modifications are done under sighand lock.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/ptrace.h | 4 ++++
include/linux/sched/signal.h | 6 ++----
kernel/ptrace.c | 27 ++++++++++++++++++---------
kernel/signal.c | 1 +
4 files changed, 25 insertions(+), 13 deletions(-)

--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -45,6 +45,10 @@ extern int ptrace_access_vm(struct task_
#define PT_TRACE_SECCOMP PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP) // 0x00000400

#define PT_SEIZED 0x00010000 /* SEIZE used, enable new behavior */// 0x00010000
+#define PT_STOPPED 0x00020000 // 0x00020000
+#define PT_STOPPED_FATAL 0x00040000 // 0x00040000
+
+#define PT_STOPPED_MASK (PT_STOPPED|PT_STOPPED_FATAL)

#define PT_EXITKILL (PTRACE_O_EXITKILL << PT_OPT_FLAG_SHIFT) // 0x00800000
#define PT_SUSPEND_SECCOMP (PTRACE_O_SUSPEND_SECCOMP << PT_OPT_FLAG_SHIFT) // 0x01000000
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -418,10 +418,8 @@ static inline void signal_wake_up(struct
{
signal_wake_up_state(t, resume ? TASK_WAKEKILL : 0);
}
-static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume)
-{
- signal_wake_up_state(t, resume ? __TASK_TRACED : 0);
-}
+
+extern void ptrace_signal_wake_up(struct task_struct *t, bool resume);

void task_join_group_stop(struct task_struct *task);

--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -64,6 +64,14 @@ int ptrace_access_vm(struct task_struct
return ret;
}

+void ptrace_signal_wake_up(struct task_struct *t, bool resume)
+{
+ lockdep_assert_task_sighand_held(t);
+
+ if (resume)
+ t->ptrace &= ~PT_STOPPED_MASK;
+ signal_wake_up_state(t, resume ? __TASK_TRACED : 0);
+}

void __ptrace_link(struct task_struct *child, struct task_struct *new_parent,
const struct cred *ptracer_cred)
@@ -197,6 +205,8 @@ static bool ptrace_freeze_traced(struct
spin_lock_irq(&task->sighand->siglock);
if (task_is_traced(task) && !looks_like_a_spurious_pid(task) &&
!__fatal_signal_pending(task)) {
+ task->ptrace &= ~PT_STOPPED_MASK;
+ task->ptrace |= PT_STOPPED;
WRITE_ONCE(task->__state, __TASK_TRACED);
ret = true;
}
@@ -218,10 +228,13 @@ static void ptrace_unfreeze_traced(struc
*/
spin_lock_irq(&task->sighand->siglock);
if (READ_ONCE(task->__state) == __TASK_TRACED) {
- if (__fatal_signal_pending(task))
+ if (__fatal_signal_pending(task)) {
+ task->ptrace &= ~PT_STOPPED_MASK;
wake_up_state(task, __TASK_TRACED);
- else
+ } else {
+ task->ptrace |= PT_STOPPED_MASK;
WRITE_ONCE(task->__state, TASK_TRACED);
+ }
}
spin_unlock_irq(&task->sighand->siglock);
}
@@ -835,8 +848,6 @@ static long ptrace_get_rseq_configuratio
static int ptrace_resume(struct task_struct *child, long request,
unsigned long data)
{
- bool need_siglock;
-
if (!valid_signal(data))
return -EIO;

@@ -877,13 +888,11 @@ static int ptrace_resume(struct task_str
* status and clears the code too; this can't race with the tracee, it
* takes siglock after resume.
*/
- need_siglock = data && !thread_group_empty(current);
- if (need_siglock)
- spin_lock_irq(&child->sighand->siglock);
+ spin_lock_irq(&child->sighand->siglock);
child->exit_code = data;
+ child->ptrace &= ~PT_STOPPED_MASK;
wake_up_state(child, __TASK_TRACED);
- if (need_siglock)
- spin_unlock_irq(&child->sighand->siglock);
+ spin_unlock_irq(&child->sighand->siglock);

return 0;
}
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2228,6 +2228,7 @@ static void ptrace_stop(int exit_code, i
return;
}

+ current->ptrace |= PT_STOPPED_MASK;
set_special_state(TASK_TRACED);

/*