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 7764BC10F0B for ; Wed, 20 Feb 2019 15:08:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3E0E42147C for ; Wed, 20 Feb 2019 15:08:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550675329; bh=H4xMU4YgNwkaIhgEmxjar2r4Os3LG9Sk4j9h4UVmSqc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=c78A6mHVyOxw9PJctQ/vGM2Acd5S/FNXoQp37Ni0iqavYOEjqImhcqaWSEL8sHX2P oPZs0PL4CiTONnhLNdy+rUgFFQiPH5sEb63BdM+Q1perNJKn+yXMde7Sh2IwqUKIRi dRgEldeoCAw3rV9K/4W8gI93++a1+n/BsFDkZeDw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727064AbfBTPIr (ORCPT ); Wed, 20 Feb 2019 10:08:47 -0500 Received: from mail.kernel.org ([198.145.29.99]:33380 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725842AbfBTPIr (ORCPT ); Wed, 20 Feb 2019 10:08:47 -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 9F8AD20859; Wed, 20 Feb 2019 15:08:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550675326; bh=H4xMU4YgNwkaIhgEmxjar2r4Os3LG9Sk4j9h4UVmSqc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=JCWxlWiWmb+kjT6/n6HizN9LkTnMGU+wZZnalTo1wTNNG7VFjjUb+HvMd5o5syo9i G8maY4PN/BQMPCwP8m8eERi9Tni+uG2z/ZsaQGCwtu17I8lFgfOWcnTpekkdKy9h5q 1ZVH4DWqfKeVpEhVqHUk7+AXrMqVXGHL8nPxulFk= Date: Thu, 21 Feb 2019 00:08:42 +0900 From: Masami Hiramatsu To: Jann Horn Cc: Steven Rostedt , Linus Torvalds , Andy Lutomirski , Linux List Kernel Mailing , Ingo Molnar , Andrew Morton , stable , Changbin Du , Kees Cook , Andy Lutomirski Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault Message-Id: <20190221000842.7026d2e4d5af89602aa5013c@kernel.org> In-Reply-To: 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> <20190220171019.5e81a4946b56982f324f7c45@kernel.org> 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 Hi Jann, On Wed, 20 Feb 2019 14:57:31 +0100 Jann Horn wrote: > On Wed, Feb 20, 2019 at 9:10 AM Masami Hiramatsu wrote: > > 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(). (*) > [...] > > (*) BTW, there is another concern to use _from_user APIs in kprobe. Are those > > APIs might sleep?? > > If you want to access userspace without sleeping, and ignore data in > non-present pages, you can do `pagefault_disable(); err = > __copy_from_user_inatomic(...); pagefault_enable();`. (Actually, maybe > the kernel should have a helper for that...) Ok, we are going back to the start point of this thread :) http://lkml.kernel.org/r/20190215174712.372898450@goodmis.org So, if user tells kprobe it is user-pointer, we check it with access_ok(), and will do something similar to the strnlen_user() and strncpy_from_user(), but using __copy_from_user_inatomic() and pagefault_disable() for kprobes. Thank you! -- Masami Hiramatsu