linux-kernel - Re: [PATCH 1/4] rethook: use preempt_{disable, enable}_notrace in rethook_trampoline

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Message-Id: <20230516143320.f0eb438f981039e59ee4a5b1@kernel.org>
Date:   Tue, 16 May 2023 14:33:20 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Masami Hiramatsu (Google) <mhiramat@...nel.org>
Cc:     Ze Gao <zegao2021@...il.com>, Steven Rostedt <rostedt@...dmis.org>,
        Ze Gao <zegao@...cent.com>, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] rethook: use preempt_{disable, enable}_notrace in
 rethook_trampoline_handler

On Tue, 16 May 2023 13:25:02 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> Hi Ze Gao,
> 
> Thanks for the patch.
> 
> On Mon, 15 May 2023 11:26:38 +0800
> Ze Gao <zegao2021@...il.com> wrote:
> 
> > This patch replace preempt_{disable, enable} with its corresponding
> > notrace version in rethook_trampoline_handler so no worries about stack
> > recursion or overflow introduced by preempt_count_{add, sub} under
> > fprobe + rethook context.
> 
> So, have you ever see that recursion of preempt_count overflow case?
> 
> I intended to use the normal preempt_disable() here because it does NOT
> prohibit any function-trace call (Note that both kprobes and
> fprobe checks recursive call by itself) but it is used for preempt_onoff
> tracer.

OK, I got the point.

  rethook_trampoline_handler() {
    preempt_disable() {
      preempt_count_add() { => fprobe and set rethook
      } => rethook_trampoline_handler() {
        preempt_disable() {
          ...   

So the problem is that the preempt_disable() macro calls preempt_count_add()
which can be tracable.

So, let's make it notrace.

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

and

Fixes: 54ecbe6f1ed5 ("rethook: Add a generic return hook")
Cc: stable@...r.kernel.org

Thank you,

> 
> Thanks,
> 
> > 
> > Signed-off-by: Ze Gao <zegao@...cent.com>
> > ---
> >  kernel/trace/rethook.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
> > index 32c3dfdb4d6a..60f6cb2b486b 100644
> > --- a/kernel/trace/rethook.c
> > +++ b/kernel/trace/rethook.c
> > @@ -288,7 +288,7 @@ unsigned long rethook_trampoline_handler(struct pt_regs *regs,
> >  	 * These loops must be protected from rethook_free_rcu() because those
> >  	 * are accessing 'rhn->rethook'.
> >  	 */
> > -	preempt_disable();
> > +	preempt_disable_notrace();
> >  
> >  	/*
> >  	 * Run the handler on the shadow stack. Do not unlink the list here because
> > @@ -321,7 +321,7 @@ unsigned long rethook_trampoline_handler(struct pt_regs *regs,
> >  		first = first->next;
> >  		rethook_recycle(rhn);
> >  	}
> > -	preempt_enable();
> > +	preempt_enable_notrace();
> >  
> >  	return correct_ret_addr;
> >  }
> > -- 
> > 2.40.1
> > 
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@...nel.org>


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