Date:   Tue, 24 Jan 2023 09:00:26 +0900
From:   Masami Hiramatsu (Google) <mhiramat@kernel.org>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     linux-trace-kernel@vger.kernel.org,
        Pengfei Xu <pengfei.xu@intel.com>,
        linux-kernel@vger.kernel.org, peterz@infradead.org,
        heng.su@intel.com, "Naveen N . Rao" <naveen.n.rao@linux.ibm.com>
Subject: Re: [PATCH] kprobes: Fix to handle forcibly unoptimized kprobes on
 freeing_list
Message-Id: <20230124090026.02d897cfe904a0af5283b6b5@kernel.org>
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References: <Y8URdIfVr3pq2X8w@xpf.sh.intel.com>
        <167448024501.3253718.13037333683110512967.stgit@devnote3>
        <20230123133931.6f6a711d@gandalf.local.home>
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On Mon, 23 Jan 2023 13:39:31 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Mon, 23 Jan 2023 22:24:05 +0900
> "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
> 
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > 
> > Sinec forcibly unoptimized kprobes will be put on the freeing_list directly
> 
> "Since"
> 
> > in the unoptimize_kprobe(), do_unoptimize_kprobes() must continue to check
> > the freeing_list even if unoptimizing_list is empty.
> > 
> > This bug can be happen if a kprobe is put in an instruction which is in the
> 
> "This bug can happen if"
> 
> > middle of the jump-replaced instruction sequence of an optprobe, *and* the
> > optprobe is recently unregistered and queued on unoptimizing_list.
> > In this case, the optprobe will be unoptimized forcibly (means immediately)
> > and put it into the freeing_list, expecting the optprobe will be handled in
> > do_unoptimize_kprobe().
> > But if there is no other optprobes on the unoptimizing_list, current code
> > returns from the do_unoptimize_kprobe() soon and do not handle the optprobe
> 
>                                               "and does not handle'
> 
> > which is on the freeing_list, and it will hit the WARN_ON_ONCE() in the
> > do_free_cleaned_kprobes(), because it is not handled in the latter loop of
> > the do_unoptimize_kprobe().
> > 
> > To solve this issue, do not return from do_unoptimize_kprobes() immediately
> > even if unoptimizing_list is empty.
> > 
> > Moreover, this change affects another case. kill_optimized_kprobes() expects
> > kprobe_optimizer() will just free the optprobe on freeing_list.
> > So I changed it to just do list_move() to freeing_list if optprobes are on
> > unoptimizing list. And the do_unoptimize_kprobe() will skip
> > arch_disarm_kprobe() if the probe on freeing_list has gone flag.
> > 
> > Link: https://lore.kernel.org/all/Y8URdIfVr3pq2X8w@xpf.sh.intel.com/
> > 
> > Fixes: e4add247789e ("kprobes: Fix optimize_kprobe()/unoptimize_kprobe() cancellation logic")
> > Reported-by: Pengfei Xu <pengfei.xu@intel.com>
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > ---
> >  kernel/kprobes.c |   23 ++++++++++-------------
> >  1 file changed, 10 insertions(+), 13 deletions(-)
> > 
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index 1c18ecf9f98b..73b150fad936 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -555,17 +555,15 @@ static void do_unoptimize_kprobes(void)
> >  	/* See comment in do_optimize_kprobes() */
> >  	lockdep_assert_cpus_held();
> >  
> > -	/* Unoptimization must be done anytime */
> > -	if (list_empty(&unoptimizing_list))
> > -		return;
> > +	if (!list_empty(&unoptimizing_list))
> > +		arch_unoptimize_kprobes(&unoptimizing_list, &freeing_list);
> >  
> > -	arch_unoptimize_kprobes(&unoptimizing_list, &freeing_list);
> > -	/* Loop on 'freeing_list' for disarming */
> > +	/* Loop on 'freeing_list' for disarming and removing from kprobe hash list */
> >  	list_for_each_entry_safe(op, tmp, &freeing_list, list) {
> >  		/* Switching from detour code to origin */
> >  		op->kp.flags &= ~KPROBE_FLAG_OPTIMIZED;
> > -		/* Disarm probes if marked disabled */
> > -		if (kprobe_disabled(&op->kp))
> > +		/* Disarm probes if marked disabled and not gone */
> > +		if (kprobe_disabled(&op->kp) && !kprobe_gone(&op->kp))
> >  			arch_disarm_kprobe(&op->kp);
> >  		if (kprobe_unused(&op->kp)) {
> >  			/*
> > @@ -797,14 +795,13 @@ static void kill_optimized_kprobe(struct kprobe *p)
> >  	op->kp.flags &= ~KPROBE_FLAG_OPTIMIZED;
> >  
> >  	if (kprobe_unused(p)) {
> > -		/* Enqueue if it is unused */
> > -		list_add(&op->list, &freeing_list);
> >  		/*
> > -		 * Remove unused probes from the hash list. After waiting
> > -		 * for synchronization, this probe is reclaimed.
> > -		 * (reclaiming is done by do_free_cleaned_kprobes().)
> > +		 * Unused kprobe is on unoptimizing or freeing list. We move it
> > +		 * to freeing_list and let the kprobe_optimizer() removes it from
> 
>                                                                  "remove it"
> 
> > +		 * the kprobe hash list and frees it.
> 
>                                         "and free it."
> 
> >  		 */
> > -		hlist_del_rcu(&op->kp.hlist);
> > +		if (optprobe_queued_unopt(op))
> > +			list_move(&op->list, &freeing_list);
> >  	}
> >  
> >  	/* Don't touch the code, because it is already freed. */
> 
> Other than the spelling issues,
> 
> Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Thanks for review! I'll fix typos and put on probes/urgent.
Also,
Cc: stable@vger.kernel.org

Thank you,

> 
> -- Steve


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