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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AA0EEC43217 for ; Tue, 26 Oct 2021 13:12:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 92F89600D4 for ; Tue, 26 Oct 2021 13:12:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236186AbhJZNOo (ORCPT ); Tue, 26 Oct 2021 09:14:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:57748 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230324AbhJZNOk (ORCPT ); Tue, 26 Oct 2021 09:14:40 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (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 18A7360C49; Tue, 26 Oct 2021 13:12:13 +0000 (UTC) Date: Tue, 26 Oct 2021 09:12:11 -0400 From: Steven Rostedt To: Yafang Shao Cc: Kees Cook , Andrew Morton , Mathieu Desnoyers , Arnaldo Carvalho de Melo , Petr Mladek , Peter Zijlstra , Al Viro , Valentin Schneider , Qiang Zhang , robdclark , christian , Dietmar Eggemann , Ingo Molnar , Juri Lelli , Vincent Guittot , David Miller , Jakub Kicinski , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin Lau , Song Liu , Yonghong Song , john fastabend , KP Singh , dennis.dalessandro@cornelisnetworks.com, mike.marciniszyn@cornelisnetworks.com, dledford@redhat.com, jgg@ziepe.ca, linux-rdma@vger.kernel.org, netdev , bpf , "linux-perf-use." , linux-fsdevel@vger.kernel.org, Linux MM , LKML , kernel test robot , kbuild test robot , Andrii Nakryiko Subject: Re: [PATCH v6 08/12] tools/bpf/bpftool/skeleton: make it adopt to task comm size change Message-ID: <20211026091211.569a7ba2@gandalf.local.home> In-Reply-To: References: <20211025083315.4752-1-laoar.shao@gmail.com> <20211025083315.4752-9-laoar.shao@gmail.com> <202110251421.7056ACF84@keescook> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; 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, 26 Oct 2021 10:18:51 +0800 Yafang Shao wrote: > > So, if we're ever going to copying these buffers out of the kernel (I > > don't know what the object lifetime here in bpf is for "e", etc), we > > should be zero-padding (as get_task_comm() does). > > > > Should this, instead, be using a bounce buffer? > > The comment in bpf_probe_read_kernel_str_common() says > > : /* > : * The strncpy_from_kernel_nofault() call will likely not fill the > : * entire buffer, but that's okay in this circumstance as we're probing > : * arbitrary memory anyway similar to bpf_probe_read_*() and might > : * as well probe the stack. Thus, memory is explicitly cleared > : * only in error case, so that improper users ignoring return > : * code altogether don't copy garbage; otherwise length of string > : * is returned that can be used for bpf_perf_event_output() et al. > : */ > > It seems that it doesn't matter if the buffer is filled as that is > probing arbitrary memory. > > > > > get_task_comm(comm, task->group_leader); > > This helper can't be used by the BPF programs, as it is not exported to BPF. > > > bpf_probe_read_kernel_str(&e.comm, sizeof(e.comm), comm); I guess Kees is worried that e.comm will have something exported to user space that it shouldn't. But since e is part of the BPF program, does the BPF JIT take care to make sure everything on its stack is zero'd out, such that a user BPF couldn't just read various items off its stack and by doing so, see kernel memory it shouldn't be seeing? I'm guessing it does, otherwise this would be a bigger issue than this patch series. -- Steve