linux-kernel - syscall_regfunc() && TIF_SYSCALL

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20120330183104.GA12927@redhat.com>
Date:	Fri, 30 Mar 2012 20:31:04 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...hat.com>, Jason Baron <jbaron@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org
Subject: syscall_regfunc() && TIF_SYSCALL_TRACEPOINT

Hello.

I've looked at syscall_regfunc/unregfunc by accident, and I am
a bit confused...

	void syscall_regfunc(void)
	{
		unsigned long flags;
		struct task_struct *g, *t;

		if (!sys_tracepoint_refcount) {
			read_lock_irqsave(&tasklist_lock, flags);

Why _irqsave? write_lock(tasklist) needs to disable irqs, but read_
doesn't. Any subtle reason I missed?

			do_each_thread(g, t) {
				/* Skip kernel threads. */
				if (t->mm)

We should check PF_KTHREAD, not ->mm.

					set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);

But the main question is, can't we race with clone() and miss the
new child? The new task is not "visible" to do_each_thread() until
copy_process()->list_add_tail_rcu(thread_group/init_task.tasks).

Don't we need something like the patch below?

Oleg.


--- x/kernel/fork.c
+++ x/kernel/fork.c
@@ -1446,7 +1446,12 @@ static struct task_struct *copy_process(
 
 	total_forks++;
 	spin_unlock(&current->sighand->siglock);
+#ifdef CONFIG_TRACEPOINTS
+	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
+		set_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT);
+#endif
 	write_unlock_irq(&tasklist_lock);
+
 	proc_fork_connector(p);
 	cgroup_post_fork(p);
 	if (clone_flags & CLONE_THREAD)

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/