1. ptrace_resume() plays with the stopped task which can be also
task_is_utraced(). In this case user_enable_xxx_step() can race
with utrace_reset()->user_disable_single_step().
We could change utrace_reset() to check ptrace_wants_step() and
add the task_utrace_lock + unlock barrier after ptrace_resume()
sets PT_SINGLE_STEP.
But it is better to reassign enable/desable from the tracer to
the tracee, it can check its PT_SINGLE_ bits after wakeup. This
also makes sense because enable_step(task) can be faster if
task == current.
2. ptrace can do user_disable_single_step() while utrace needs the
stepping.
Set TIF_NOTIFY_RESUME after user_disable_single_step() to ensure
the tracee can't return to the user-space without utrace_resume().
Any correct engine which wants the stepping should reassert it.
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
kernel/ptrace.c | 4 ----
kernel/signal.c | 12 ++++++++++++
2 files changed, 12 insertions(+), 4 deletions(-)
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 44908d0..d37b30d 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -580,14 +580,10 @@ static int ptrace_resume(struct task_struct *child, long
request,
if (unlikely(!arch_has_block_step()))
return -EIO;
child->ptrace |= PT_SINGLE_BLOCK;
- user_enable_block_step(child);
} else if (is_singlestep(request) || is_sysemu_singlestep(request)) {
if (unlikely(!arch_has_single_step()))
return -EIO;
child->ptrace |= PT_SINGLE_STEP;
- user_enable_single_step(child);
- } else {
- user_disable_single_step(child);
}
child->exit_code = data;
diff --git a/kernel/signal.c b/kernel/signal.c
index d0e0c67..bc40bd7 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1840,6 +1840,18 @@ static void ptrace_stop(int exit_code, int why, int
clear_code, siginfo_t *info)
}
tracehook_finish_stop();
+
+ if (current->ptrace & PT_SINGLE_BLOCK)
+ user_enable_block_step(current);
+ else if (current->ptrace & PT_SINGLE_STEP)
+ user_enable_single_step(current);
+ else {
+ user_disable_single_step(current);
+ /* if utrace needs the stepping it should reassert */
+ if (task_utrace_flags(current))
+ set_thread_flag(TIF_NOTIFY_RESUME);
+ }
+
/*
* While in TASK_TRACED, we were considered "frozen enough".
* Now that we woke up, it's crucial if we're supposed to be
--
1.5.5.1
