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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS 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 1CD5BC43381 for ; Thu, 28 Feb 2019 12:29:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E08A72171F for ; Thu, 28 Feb 2019 12:29:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551356964; bh=pNtoIm19/RbLA530zaYV92DVB139pC7B3avkF0tQ5PI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=1Fwj/L+qWSiwkoNSLhDN4QyjfnXVUF4J1BqiVL3yXBKWs44yXd1bbvPRm5tdKG5K3 Sc7hHv+a7j0+JUy+7w9mlmVjutBZVbUchHw25sHkWXMQiQaITueMZvK2hGWfbetqkA MBzcrC1mRW4APR1YHivLJ7ncCm4Xq4aMrYEM0L0c= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731552AbfB1M3T (ORCPT ); Thu, 28 Feb 2019 07:29:19 -0500 Received: from mail.kernel.org ([198.145.29.99]:35110 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730960AbfB1M3S (ORCPT ); Thu, 28 Feb 2019 07:29:18 -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 581EA2083D; Thu, 28 Feb 2019 12:29:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551356957; bh=pNtoIm19/RbLA530zaYV92DVB139pC7B3avkF0tQ5PI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=omgd/yZw4ojeqpb7pfcFA91qgLNCXdlJselo4cKLcltpHI98GV7a0T7uHggPLa8WA tepmvVe/uMhQ7Ro4odpHy5ahACxo867l86bYRTiVnqHP8Ty8VgAcRUnbUvBwH2kiZT MuXa1i+GYgtRKwzwksjLc6nwFE1AaJaJAJTs/bqQ= Date: Thu, 28 Feb 2019 21:29:13 +0900 From: Masami Hiramatsu To: Joel Fernandes Cc: Alexei Starovoitov , Linus Torvalds , Masami Hiramatsu , 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 Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault Message-Id: <20190228212913.20079490b3df88d285664a56@kernel.org> In-Reply-To: <20190226152447.GA99670@google.com> References: <20190219111802.1d6dbaa3@gandalf.local.home> <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> 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: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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. Thank you, -- Masami Hiramatsu