linux-kernel - Re: [RFC] kretprobe: Prevent triggering kretprobe from within kprobe_flush

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Date:   Tue, 14 Apr 2020 18:03:38 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Peter Zijlstra <peterz@...radead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "bibo,mao" <bibo.mao@...el.com>,
        "Ziqian SUN (Zamir)" <zsun@...hat.com>
Subject: Re: [RFC] kretprobe: Prevent triggering kretprobe from within
 kprobe_flush_task

On Fri, Apr 10, 2020 at 09:31:59AM +0900, Masami Hiramatsu wrote:

SNIP

> > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> > index 4d7022a740ab..081d0f366c99 100644
> > --- a/arch/x86/kernel/kprobes/core.c
> > +++ b/arch/x86/kernel/kprobes/core.c
> > @@ -757,12 +757,33 @@ static struct kprobe kretprobe_kprobe = {
> >  	.addr = (void *)kretprobe_trampoline,
> >  };
> >  
> > +void arch_kprobe_reject_section_start(void)
> > +{
> > +	struct kprobe_ctlblk *kcb;
> > +
> > +	preempt_disable();
> > +
> > +	/*
> > +	 * Set a dummy kprobe for avoiding kretprobe recursion.
> > +	 * Since kretprobe never run in kprobe handler, kprobe must not
> > +	 * be running behind this point.
> > +	 */
> > +	__this_cpu_write(current_kprobe, &kretprobe_kprobe);
> > +	kcb = get_kprobe_ctlblk();
> > +	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> > +}
> 
> Yeah, the code seems good to me.
> 
> BTW, I rather like make it arch independent function so that other
> arch can use it. In this case, the dummy kprobe's addr should be
> somewhere obviously blacklisted (but it must be accessible.)
> I think get_kprobe() will be a candidate.

right.. as Ziqian noted we see this on other ppc as well

> 
> And (sorry about changing my mind), the naming, I think kprobe_busy_begin()
> and kprobe_busy_end() will be better because it doesn't reject registering
> kprobes, instead, just make it busy :)

ok, will change 

thanks,
jirka