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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 1B551C43381 for ; Thu, 28 Feb 2019 15:18:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DAA0220C01 for ; Thu, 28 Feb 2019 15:18:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="JohBYW/e" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388909AbfB1PSq (ORCPT ); Thu, 28 Feb 2019 10:18:46 -0500 Received: from mail-qk1-f196.google.com ([209.85.222.196]:32823 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732587AbfB1PSm (ORCPT ); Thu, 28 Feb 2019 10:18:42 -0500 Received: by mail-qk1-f196.google.com with SMTP id x9so12308736qkf.0 for ; Thu, 28 Feb 2019 07:18:41 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=LHYYDw5IEr0Z3bfIZUydUHRrCoTE6ihZjbQOgO4Vu+4=; b=JohBYW/eB1ksawkZAU2cGTJ9LcqYmCdrmb2fSytbx4rI1ZIaoN99CgXI9uBzpXCrSq gK+42HPYcCAcRyi9lz2e+234+Bsw3Ou7wYBNtsDfbqJIuPo6IHs5+q8qaTcEd3aC0e5N 73Up1gt6sJuQL7rrBEAor44MynmF2OvknxGVU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=LHYYDw5IEr0Z3bfIZUydUHRrCoTE6ihZjbQOgO4Vu+4=; b=iesNqXBXzGa2O17TYGu/X6czIdCqthxr2exXRmdFNn+1vrGHFdsjO9QUzpSM/WMuWD 1mjkf4iPtd0d5gIf57qDnLSt9+1Loqnl5A8vBQQbGQi/FO20Mgyb1TysjaUSQnORoSFc g/Z07adoOxqK73n+pSSfvOYtIeq9G2eBviRMOL9s3H6/PYUcJV9cuqc0KuzYXwa0wT1b cw8K1z68WcY8P2zTJ7RwPJqFxTV2KnLZupYlk8R22C+xe71Bz9cEwFh5rsQxQ+v+TxAh /MsnjCSapYRB4/BdN86S2yW2r/xUjLmj53DhbBZGSLd0LAYxgOCARvPQ3FV07cfzrdUk KwHg== X-Gm-Message-State: AHQUAuYaYL1y6yHDKzbIok0GefkoMEtDFOYXaTIdMkpOY09SsLYFz3ML L+cx3XNCf7QS4P9AuGetNXdKxA== X-Google-Smtp-Source: AHgI3IYHOWk/O1OBon0oIYArBhTiNa0+ysDbEu45eFkvPTAk1MwBlKOylPtF0WYScASqKHC3jBdJ8Q== X-Received: by 2002:a05:620a:1333:: with SMTP id p19mr6556301qkj.165.1551367120811; Thu, 28 Feb 2019 07:18:40 -0800 (PST) Received: from localhost ([2620:0:1004:1100:cca9:fccc:8667:9bdc]) by smtp.gmail.com with ESMTPSA id r47sm12488154qtc.48.2019.02.28.07.18.39 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 28 Feb 2019 07:18:39 -0800 (PST) Date: Thu, 28 Feb 2019 10:18:39 -0500 From: Joel Fernandes To: Masami Hiramatsu Cc: Alexei Starovoitov , Linus Torvalds , Steven Rostedt , Andy Lutomirski , will.deacon@arm.com, Linux List Kernel Mailing , Ingo Molnar , Andrew Morton , stable , Changbin Du , Jann Horn , Kees Cook , Andy Lutomirski , daniel@iogearbox.net, netdev@vger.kernel.org, bpf@vger.kernel.org, yhs@fb.com Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault Message-ID: <20190228151839.GA159251@google.com> References: <20190219140330.5dd9e876@gandalf.local.home> <20190220171019.5e81a4946b56982f324f7c45@kernel.org> <20190220094926.0ab575b3@gandalf.local.home> <20190222172745.2c7205d62003c0a858e33278@kernel.org> <20190222173509.88489b7c5d1bf0e2ec2382ee@kernel.org> <20190222192703.epvgxghwybte7gxs@ast-mbp.dhcp.thefacebook.com> <20190226152447.GA99670@google.com> <20190228212913.20079490b3df88d285664a56@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190228212913.20079490b3df88d285664a56@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 28, 2019 at 09:29:13PM +0900, Masami Hiramatsu wrote: > On Tue, 26 Feb 2019 10:24:47 -0500 > Joel Fernandes wrote: > > > On Fri, Feb 22, 2019 at 11:27:05AM -0800, Alexei Starovoitov wrote: > > > On Fri, Feb 22, 2019 at 09:43:14AM -0800, Linus Torvalds wrote: > > > > > > > > Then we should still probably fix up "__probe_kernel_read()" to not > > > > allow user accesses. The easiest way to do that is actually likely to > > > > use the "unsafe_get_user()" functions *without* doing a > > > > uaccess_begin(), which will mean that modern CPU's will simply fault > > > > on a kernel access to user space. > > > > > > On bpf side the bpf_probe_read() helper just calls probe_kernel_read() > > > and users pass both user and kernel addresses into it and expect > > > that the helper will actually try to read from that address. > > > > Slightly related and FWIW, BCC's eBPF-based opensnoop tool [1] installs a > > kprobe on do_sys_open to monitor calls to the open syscall globally. > > > > do_sys_open() has prototype: > > > > long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode); > > > > This causes a "blank" filename to be displayed by opensnoop when I run it on > > my Pixel 3 (arm64), possibly because this is a user pointer. However, it > > works fine on x86-64. > > > > So it seems to me that on arm64, reading user pointers directly still doesn't > > work even if there is a distinction between user/kernel addresses. In that > > case reading the user pointer using user accessors (possibly using > > bpf_probe_user_read helper) should be needed to fix this issue (as Yonghong > > also privately discussed with me). > > OK, it sounds like the same issue. Please add a bpf_user_read() and use it > for __user pointer. CC'd Yonghong who said eariler to me he would add it, but I could add it too if he wants me to. thanks, - Joel