linux-kernel - Re: [PATCH v2] kprobes: Use synchronize_rcu_tasks_rude in kprobe

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

Message-Id: <20240119212850.a46eeaec8083770c5abad81a@kernel.org>
Date: Fri, 19 Jan 2024 21:28:50 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Chen Zhongjin <chenzhongjin@...wei.com>, <linux-kernel@...r.kernel.org>,
 <linux-trace-kernel@...r.kernel.org>, <yangjihong1@...wei.com>,
 <naveen.n.rao@...ux.ibm.com>, <anil.s.keshavamurthy@...el.com>,
 <davem@...emloft.net>, <paulmck@...nel.org>, <mhiramat@...nel.org>,
 <akpm@...ux-foundation.org>, <tglx@...utronix.de>, <peterz@...radead.org>,
 <pmladek@...e.com>, <dianders@...omium.org>, <npiggin@...il.com>,
 <mpe@...erman.id.au>, <jkl820.git@...il.com>,
 <juerg.haefliger@...onical.com>, <rick.p.edgecombe@...el.com>,
 <eric.devolder@...cle.com>, <mic@...ikod.net>
Subject: Re: [PATCH v2] kprobes: Use synchronize_rcu_tasks_rude in
 kprobe_optimizer

On Wed, 17 Jan 2024 21:26:46 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Thu, 18 Jan 2024 02:18:42 +0000
> Chen Zhongjin <chenzhongjin@...wei.com> wrote:
> 
> > There is a deadlock scenario in kprobe_optimizer():
> > 
> > pid A				pid B			pid C
> > kprobe_optimizer()		do_exit()		perf_kprobe_init()
> > mutex_lock(&kprobe_mutex)	exit_tasks_rcu_start()	mutex_lock(&kprobe_mutex)
> > synchronize_rcu_tasks()		zap_pid_ns_processes()	// waiting kprobe_mutex
> > // waiting tasks_rcu_exit_srcu	kernel_wait4()
> > 				// waiting pid C exit
> > 
> > To avoid this deadlock loop, use synchronize_rcu_tasks_rude() in kprobe_optimizer()
> > rather than synchronize_rcu_tasks(). synchronize_rcu_tasks_rude() can also promise
> > that all preempted tasks have scheduled, but it will not wait tasks_rcu_exit_srcu.
> > 

At first, thanks for finding this scenario! 

> 
> Did lockdep detect this? If not, we should fix that.

Can lockdep find rcu and wait4 related one?

> 
> I'm also thinking if we should find another solution, as this seems more of
> a work around than a fix.

Hmm, IIUC, we may need a synchronizer which will return -EBUSY if
someone starts waiting in exit_tasks_rcu_start(). Then optimizer 
can unlock the mutex and retry it.

Thank you,

> 
> > Fixes: a30b85df7d59 ("kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y")
> > Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
> > ---
> > v1 -> v2: Add Fixes tag
> > ---
> >  arch/Kconfig     | 2 +-
> >  kernel/kprobes.c | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index f4b210ab0612..dc6a18854017 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -104,7 +104,7 @@ config STATIC_CALL_SELFTEST
> >  config OPTPROBES
> >  	def_bool y
> >  	depends on KPROBES && HAVE_OPTPROBES
> > -	select TASKS_RCU if PREEMPTION
> > +	select TASKS_RUDE_RCU
> 
> Is this still a bug if PREEMPTION is not enabled?
> 
> -- Steve
> 
> >  
> >  config KPROBES_ON_FTRACE
> >  	def_bool y
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index d5a0ee40bf66..09056ae50c58 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -623,7 +623,7 @@ static void kprobe_optimizer(struct work_struct *work)
> >  	 * Note that on non-preemptive kernel, this is transparently converted
> >  	 * to synchronoze_sched() to wait for all interrupts to have completed.
> >  	 */
> > -	synchronize_rcu_tasks();
> > +	synchronize_rcu_tasks_rude();
> >  
> >  	/* Step 3: Optimize kprobes after quiesence period */
> >  	do_optimize_kprobes();
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>