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 X-Spam-Level: X-Spam-Status: No, score=-1.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3754AC10F01 for ; Wed, 20 Feb 2019 08:10:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0D8352183F for ; Wed, 20 Feb 2019 08:10:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550650227; bh=sdBSnPGZCdOugb7YD6in1/WyjYmSKxm9lOA3pX/1Qi8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=CnHy/KMSTaZWn0rko9MV3guXPWjVLarA1odV2nsUS4syH290E5E/mRRxKmsFCpRkJ DNHkbsfKNcm4BBG72dnFHKjx41XYAfcpdcJfQ+YjNdstVEQKJin5D7V7XhU8v9ur2l Lifhlx7DrwZak7tDEriDNNeT1VC3O64eyXxqp6CM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726093AbfBTIKZ (ORCPT ); Wed, 20 Feb 2019 03:10:25 -0500 Received: from mail.kernel.org ([198.145.29.99]:38206 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725779AbfBTIKZ (ORCPT ); Wed, 20 Feb 2019 03:10:25 -0500 Received: from devbox (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (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 CC4352146E; Wed, 20 Feb 2019 08:10:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550650223; bh=sdBSnPGZCdOugb7YD6in1/WyjYmSKxm9lOA3pX/1Qi8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=d3IXOV9UlcC06vTvHLtGLqTC7MVKY0AXNbeAlIrg6ReBnLvXLwAVyGncEt+siCqe6 InxijhSaOMmfim3qxf91z6t7zEw5Sxxwo9rizOPovCjmplwiQSlSpgkQI9uVDMKjlH jAVmS8LW4vNtThmBvH1XXZNHKqHOc2or2kqhMsFc= Date: Wed, 20 Feb 2019 17:10:19 +0900 From: Masami Hiramatsu To: Steven Rostedt Cc: Linus Torvalds , Andy Lutomirski , Linux List Kernel Mailing , Ingo Molnar , Andrew Morton , stable , Changbin Du , Jann Horn , Kees Cook , Andy Lutomirski , Masami Hiramatsu Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault Message-Id: <20190220171019.5e81a4946b56982f324f7c45@kernel.org> In-Reply-To: <20190219140330.5dd9e876@gandalf.local.home> References: <20190215174712.372898450@goodmis.org> <20190215174945.557218316@goodmis.org> <20190215171539.4682f0b4@gandalf.local.home> <300C4516-A093-43AE-8707-1C42486807A4@amacapital.net> <20190215191949.04604191@gandalf.local.home> <20190219111802.1d6dbaa3@gandalf.local.home> <20190219140330.5dd9e876@gandalf.local.home> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 19 Feb 2019 14:03:30 -0500 Steven Rostedt wrote: > > > Basically, a kprobe is mostly used for debugging what's happening in a > > > live kernel, to read any address. > > > > My point is that "any address" is not sufficient to begin with. You > > need "kernel or user". > > > > Having a flag for what _kind_ of kernel address is ok might then be > > required for other cases if they might not be ok with following page > > tables to IO space.. > > > > Good point. Looks like we should add a new flag for kprobe > trace parameters, that tell kprobes if the address is expected to be > user or kernel. That would be good regardless of the duplicate > meanings, as we could use copy_from_user without touching KERNEL_DS, if > the probe argument specifically states "this is user space". For > example, when probing do_sys_open, and you want to read what path string > was passed into the kernel. > > Masami, thoughts? Let me ensure what you want. So you want to access a "string" in user-space, not a data structure? In that case, it is very easy to me. It is enough to add a "ustring" type to kprobe events. For example, do_sys_opsn's path variable is one example. That will be +0(+0(%si)):ustring, and fetcher finally copy the string using strncpy_from_user() instead of strncpy_from_unsafe(). (*) But if you consider to access a field in a data-structure in user space, it might need some more work (E.g. ioctl's parameter), becase if the __user pointer to the data structure is on the memory, we have to dereference the address inside kernel using probe_kernel_read(), but after getting the data strucutre address, we have to dereference the address with copy_from_user(). At this moment, we have no such strong syntax... To solve that, maybe we need to introduce something like "back reference" of arguments in the event, e.g. p somewhere user_data=+0(%si) field_val=+8(\user_data):u32:user or p somewhere +0(%si) field_val=+8(\1):u32:user This ":user" additional suffix tells kprobe events to change fetching method to fetch the data by copy_from_user(). (*) BTW, there is another concern to use _from_user APIs in kprobe. Are those APIs might sleep?? Thank you, -- Masami Hiramatsu