From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.9 required=5.0 tests=DKIM_SIGNED, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,T_DKIM_INVALID autolearn=unavailable autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 6AA507D09D for ; Wed, 20 Jun 2018 08:28:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751648AbeFTI0q (ORCPT ); Wed, 20 Jun 2018 04:26:46 -0400 Received: from mail.kernel.org ([198.145.29.99]:40812 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751376AbeFTI0m (ORCPT ); Wed, 20 Jun 2018 04:26:42 -0400 Received: from devnote (s169.156.222.122.fls.vectant.ne.jp [122.222.156.169]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B8295208B1; Wed, 20 Jun 2018 08:26:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1529483201; bh=hZwrbMMqqWAxNUQhwa1MEzaQiwuLMdG072nwHl5Flz0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=hq3/j2aD+VzbAhzZAuO1MM4nCwfE3uVdWfrdOE6RfnO3/8mz0sJOOR0PdUfPd8pXo Wyw+xe5gWVIOwpCDAWQSbY2t2EH/BNEE5b8rVPhAkwdLWF0a7pX7ei0ZR8EhlfgWfZ VMj42u4Ae+GbfRMJVj68jxiP44RtYVRY+e7g9AQ4= Date: Wed, 20 Jun 2018 17:26:37 +0900 From: Masami Hiramatsu To: Randy Dunlap Cc: Thomas Gleixner , Ingo Molnar , 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 Subject: Re: [PATCH -tip v6 26/27] Documentation: kprobes: Add how to change the execution path Message-Id: <20180620172637.35916da482442b6ab139c7dc@kernel.org> In-Reply-To: <706832c5-dab4-f806-96d6-2cdc37203d9d@infradead.org> References: <152942424698.15209.15245996287444292393.stgit@devbox> <152942500680.15209.12374262914863044775.stgit@devbox> <706832c5-dab4-f806-96d6-2cdc37203d9d@infradead.org> X-Mailer: Sylpheed 3.5.0 (GTK+ 2.24.30; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, 19 Jun 2018 09:31:49 -0700 Randy Dunlap wrote: > 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... Hi Randy, Thank you for your suggestions! All of those are good to me. I'll fix it:) Thank you! > > > > +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 -- Masami Hiramatsu -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html