From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758348AbdKGRPG (ORCPT ); Tue, 7 Nov 2017 12:15:06 -0500 Received: from mail.kernel.org ([198.145.29.99]:39192 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753243AbdKGRPE (ORCPT ); Tue, 7 Nov 2017 12:15:04 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6606F218D0 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=jeyu@kernel.org Date: Tue, 7 Nov 2017 18:14:56 +0100 From: Jessica Yu To: Steven Rostedt Cc: Masami Hiramatsu , Ananth N Mavinakayanahalli , Anil S Keshavamurthy , "David S . Miller" , Ingo Molnar , Petr Mladek , Josh Poimboeuf , Joe Lawrence , Jiri Kosina , Miroslav Benes , live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: kprobes: propagate error from arm_kprobe_ftrace() Message-ID: <20171107171455.iegqpye6wpvhztd5@redbean> References: <20171102163334.3947-1-jeyu@kernel.org> <20171102163334.3947-2-jeyu@kernel.org> <20171103100317.01db273b@vmware.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20171103100317.01db273b@vmware.local.home> X-OS: Linux redbean 4.14.0-rc7-next-20171102+ x86_64 User-Agent: NeoMutt/20171027 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org +++ Steven Rostedt [03/11/17 10:03 -0400]: >On Thu, 2 Nov 2017 17:33:33 +0100 >Jessica Yu wrote: > >> Improve error handling when arming ftrace-based kprobes. Specifically, if >> we fail to arm a ftrace-based kprobe, register_kprobe()/enable_kprobe() >> should report an error instead of success. Previously, this has lead to >> confusing situations where register_kprobe() would return 0 indicating >> success, but the kprobe would not be functional if ftrace registration >> during the kprobe arming process had failed. We should therefore take any >> errors returned by ftrace into account and propagate this error so that we >> do not register/enable kprobes that cannot be armed. This can happen if, >> for example, register_ftrace_function() finds an IPMODIFY conflict (since >> kprobe_ftrace_ops has this flag set) and returns an error. Such a conflict >> is possible since livepatches also set the IPMODIFY flag for their ftrace_ops. >> >> arm_all_kprobes() keeps its current behavior and attempts to arm all >> kprobes. It returns the last encountered error and gives a warning if >> not all kprobes could be armed. >> >> This patch is based on Petr Mladek's original patchset (patches 2 and 3) >> back in 2015, which improved kprobes error handling, found here: >> >> https://lkml.org/lkml/2015/2/26/452 >> >> However, further work on this had been paused since then and the patches >> were not upstreamed. >> >> Based-on-patches-by: Petr Mladek >> Signed-off-by: Jessica Yu >> --- >> kernel/kprobes.c | 88 ++++++++++++++++++++++++++++++++++++++++---------------- >> 1 file changed, 63 insertions(+), 25 deletions(-) >> >> diff --git a/kernel/kprobes.c b/kernel/kprobes.c >> index da2ccf142358..f4a094007cb5 100644 >> --- a/kernel/kprobes.c >> +++ b/kernel/kprobes.c >> @@ -978,18 +978,27 @@ static int prepare_kprobe(struct kprobe *p) >> } >> >> /* Caller must lock kprobe_mutex */ >> -static void arm_kprobe_ftrace(struct kprobe *p) >> +static int arm_kprobe_ftrace(struct kprobe *p) >> { >> - int ret; >> + int ret = 0; >> >> ret = ftrace_set_filter_ip(&kprobe_ftrace_ops, >> (unsigned long)p->addr, 0, 0); >> - WARN(ret < 0, "Failed to arm kprobe-ftrace at %p (%d)\n", p->addr, ret); >> - kprobe_ftrace_enabled++; >> - if (kprobe_ftrace_enabled == 1) { >> + if (WARN(ret < 0, "Failed to arm kprobe-ftrace at %p (%d)\n", p->addr, ret)) >> + return ret; >> + >> + if (kprobe_ftrace_enabled == 0) { >> ret = register_ftrace_function(&kprobe_ftrace_ops); >> - WARN(ret < 0, "Failed to init kprobe-ftrace (%d)\n", ret); >> + if (WARN(ret < 0, "Failed to init kprobe-ftrace (%d)\n", ret)) >> + goto err_ftrace; >> } >> + >> + kprobe_ftrace_enabled++; >> + return ret; >> + >> +err_ftrace: >> + ftrace_set_filter_ip(&kprobe_ftrace_ops, (unsigned long)p->addr, 1, 0); > >Hmm, this could have a very nasty side effect. If you remove a function >from the ops, and it was the last function, an empty ops means to trace >*all* functions. Good point, and yes, normally this would be the (undesirable) outcome. However in this case, kprobes_ftrace_ops has the IPMODIFY flag set, so ftrace_set_filter_ip() will not allow the removal of a function if it is the very last function, and it will return an error in __ftrace_hash_update_ipmodify(). The comment there explains, if IPMODIFY is set, "return -EINVAL if the new_hash tries to trace all recs". So I think we are safe here... >Perhaps you want to add it to the "notrace" list. Which would require >implementing a ftrace_set_notrace_ip() function. Which I believe is >what you want. Any function in the notrace hash will have the same >functions in the filter hash be ignored. I think this would've been a good alternative if we wanted to protect against the empty ops case, but IPMODIFY is also incompatible with notrace.. (See: commit f8b8be8a310 and this comment here: https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg688632.html) Speaking of IPMODIFY, a question for Masami - is this flag still relevant/needed for kprobes, since jprobes has been deprecated recently? IIRC, IPMODIFY was needed in the first place because jprobes and livepatch were in direct conflict, but I recall some work being done in the past to remove the IPMODIFY flag from kprobes, but I don't think this was ever upstreamed. (See: https://patchwork.kernel.org/patch/5352481/) Thanks! Jessica