From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:46284 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965953AbeFSQbx (ORCPT ); Tue, 19 Jun 2018 12:31:53 -0400 Subject: Re: [PATCH -tip v6 26/27] Documentation: kprobes: Add how to change the execution path References: <152942424698.15209.15245996287444292393.stgit@devbox> <152942500680.15209.12374262914863044775.stgit@devbox> From: Randy Dunlap Message-ID: <706832c5-dab4-f806-96d6-2cdc37203d9d@infradead.org> Date: Tue, 19 Jun 2018 09:31:49 -0700 MIME-Version: 1.0 In-Reply-To: <152942500680.15209.12374262914863044775.stgit@devbox> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Masami Hiramatsu , Thomas Gleixner , Ingo Molnar Cc: Ingo Molnar , "H . Peter Anvin" , linux-kernel@vger.kernel.org, Ananth N Mavinakayanahalli , Andrew Morton , Steven Rostedt , linux-arch@vger.kernel.org, Jonathan Corbet , linux-doc@vger.kernel.org Message-ID: <20180619163149.ZuJiebOzjyst8S1LRrLHNcXUug6goFdj7C-LZOuJ1gE@z> On 06/19/2018 09:16 AM, Masami Hiramatsu wrote: > Add a section that explaining how to change the execution > path with kprobes and warnings for some arch. > > Signed-off-by: Masami Hiramatsu > Cc: Jonathan Corbet > Cc: linux-doc@vger.kernel.org > --- > Documentation/kprobes.txt | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt > index 3e9e99ea751b..8a98eed1521b 100644 > --- a/Documentation/kprobes.txt > +++ b/Documentation/kprobes.txt > @@ -80,6 +80,26 @@ After the instruction is single-stepped, Kprobes executes the > "post_handler," if any, that is associated with the kprobe. > Execution then continues with the instruction following the probepoint. > Hi, I have a few small suggestions... > +Changing Execution Path > +----------------------- > + > +Since the kprobes can probe into a running kernel code, it can change Since kprobes can probe into running kernel code, it can change > +the register set, including instruction pointer. This operation > +requires maximum attention, such as keeping the stack frame, recovering > +execution path etc. Since it is operated on running kernel and need deep Since it operates on a running kernel and needs deep > +knowladge of the archtecture and concurrent computing, you can easily knowledge of the architecture > +shot your foot. shoot > + > +If you change the instruction pointer (and set up other related > +registers) in pre_handler, you must return !0 so that the kprobes so that kprobes > +stops single stepping and just returns to given address. to the given address. > +This also means post_handler should not be called anymore. > + > +Note that this operation may be harder on some architectures which > +use TOC (Table of Contents) for function call, since you have to > +setup new TOC for your function in your module, and recover old setup a new TOC for your function in your module, and recover the old > +one after back from it. one after returning from it. > + > Return Probes > ------------- -- ~Randy