From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 72A80C433F5 for ; Wed, 1 Dec 2021 01:53:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345579AbhLABxa (ORCPT ); Tue, 30 Nov 2021 20:53:30 -0500 Received: from ams.source.kernel.org ([145.40.68.75]:37376 "EHLO ams.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230168AbhLABx2 (ORCPT ); Tue, 30 Nov 2021 20:53:28 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id E109BB81BBC for ; Wed, 1 Dec 2021 01:50:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C39DAC53FCB; Wed, 1 Dec 2021 01:50:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1638323406; bh=0mwtVUg0Pjtr2xBEyZ4NHyUmo7aycFpcv9dwp7BLvCo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=GNFVE43Bi7zLPvCSK+0s10l/HyHQds5YiK5hQcLOvFMvOcJJlmugeac8ZbqHJ0eBl Uhe31sh2eCyOSI74CMHkmof0VsNJp5PLOvMqNGLw020xiumR0NIDWBph+yIR9prOQs RRvXX7Dq7VCXzmEZoo8CBsPP53mt1xFyqRuvVKdl83b7VDnpIoTqDFffS7J1XBMIch WseKCriThB7LFmOy/dCnrEa6jpuK4d9iO/oGGs3eSO7fIov6jBPLL73hLWCZr5exA4 7YGKmHAHsbgdUpvqCBm9Bd+wwwWzRVz+N2ykpEKDp5IM0tzhTMGL20gtuwRhEP14tD 1iBTFrttuQAlA== Date: Wed, 1 Dec 2021 10:50:01 +0900 From: Masami Hiramatsu To: "liuqi (BA)" Cc: Linuxarm , Mark Rutland , , , , , , , , , , , Subject: Re: [PATCH v4 2/2] arm64: kprobe: Enable OPTPROBE for arm64 Message-Id: <20211201105001.5164f98ba783e7207df1229c@kernel.org> In-Reply-To: <9fdb2ad3-539f-fb4d-7a96-c737fec967f7@huawei.com> References: <20210818073336.59678-1-liuqi115@huawei.com> <20210818073336.59678-3-liuqi115@huawei.com> <20210824105001.GA96738@C02TD0UTHF1T.local> <20211127212302.f71345c34e5a62e5e779adb2@kernel.org> <4998f219-eb47-a07c-b3ed-c2ae46a77230@huawei.com> <20211129140040.87c5f423a72c95c90602c2c6@kernel.org> <3f8c1754-b677-971c-2e04-a04678206424@huawei.com> <20211129233514.e59d953a7d90d9f4f3d6a097@kernel.org> <9fdb2ad3-539f-fb4d-7a96-c737fec967f7@huawei.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 30 Nov 2021 14:48:06 +0800 "liuqi (BA)" wrote: > > > On 2021/11/29 22:35, Masami Hiramatsu wrote: > >>>>>> Hi all, > >>>>>> > >>>>>> I meet a problem when I use SYM_CODE_START(optprobe_template) to replace > >>>>>> optprobe_template_entry. > >>>>>> > >>>>>> If SYM_CODE_START is used, all optprobe will share one trampoline space. > >>>>>> Under this circumstances, if user register two optprobes, trampoline > >>>>>> will be overwritten by the newer one, and this will cause kernel panic > >>>>>> when the old optprobe is trigger. > >>>>> Hm, this is curious, because the template should be copied to the > >>>>> trampoline buffer for each optprobe and be modified. > >>>>> > >>>>>> Using optprobe_template_entry will not have this problem, as each > >>>>>> optprobe has its own trampoline space (alloced in get_opinsn_slot()). > >>>>> Yes, it is designed to do so. > >>>>> > >>>>> Thank you, > >>>>> > >>>> Hi Masami, > >>>> > >>>> Thanks for your reply. But I also met a problem when using > >>>> get_opinsn_slot() to alloc trampoline buffer. > >>>> > >>>> As module_alloc(like x86) is used to alloc buffer, trampoline is in > >>>> module space, so if origin insn is in kernel space, the range between > >>>> origin insn and trampoline is out of 128M. > >>>> > >>>> As module PLT cannot used here, I have no idea to achieve long jump in > >>>> this situation. Do you have any good idea? > >> Hi Masami, > >> > >> Thanks so much for your reply. > >> > >>> One possible solution is to use pre-allocated trampoline space in > >>> the text area, as same as ppc64 does. > >>> (See arch/powerpc/kernel/optprobes_head.S, it embeds a space at "optinsn_slot") > >>> > >> I find something interesting in arch/powerpc/kernel/optprobes.c, it use > >> "optinsn_slot" as a public buffer, and use a static "insn_page_in_use" > >> to make sure there is only one optprobe in kernel. > >> > >> If we use this solution , users could only register one optprobe each > >> time. This will also be a limitation for users, what's your opinion > >> about this? > > No, that is just a memory area for pooling trampoline buffer. So optprobe > > can allocate the buffer from that area. Please see kernel/kprobes.c:344. > > optprobe allocates "insn_slot" from kprobe_optinsn_slots, which uses > > alloc_optinsn_page() to allocate the pool of slots. > > > > Thank you, > > > > Hi, > > Thanks for your reply, I test alloc_optinsn_page() and it does work well > to alloc the pool of slots. > > But when I tried to use module PLT, something seems wrong here. > Arm64 Module PLT in mod->arch.ftrace_trampolines is set in > module_finalize, after that, mod->arch.ftrace_trampolines seems to be a > read-only memory. But in arch_optimize_kprobes() we need to modify the > destination of PLT (as each optprobe has its own trampoline buffer), if > so, we cannot get rid of the 128M branch limit :( Hmm, OK, we need to introduce trampoline buffer allocation pool for modules for such arch. But that should be another story. I think you should start from the core-kernel. At this moment, if the probe address is in the module, please return -ERANGE from arch_prepare_optimized_kprobe(). Module support must be done in the next step (series), since that will involve the kprobes generic code change. Thank you, > > Thanks, > Qi -- Masami Hiramatsu