From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751882AbbCVSDu (ORCPT ); Sun, 22 Mar 2015 14:03:50 -0400 Received: from mail-ig0-f174.google.com ([209.85.213.174]:34768 "EHLO mail-ig0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751776AbbCVSDr (ORCPT ); Sun, 22 Mar 2015 14:03:47 -0400 Message-ID: <550F0402.80900@plumgrid.com> Date: Sun, 22 Mar 2015 11:03:46 -0700 From: Alexei Starovoitov User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Masami Hiramatsu CC: Ingo Molnar , Steven Rostedt , Namhyung Kim , Arnaldo Carvalho de Melo , Jiri Olsa , "David S. Miller" , Daniel Borkmann , Peter Zijlstra , linux-api@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v9 tip 3/9] tracing: attach BPF programs to kprobes References: <1426894210-27441-1-git-send-email-ast@plumgrid.com> <1426894210-27441-4-git-send-email-ast@plumgrid.com> <550D60C2.8010502@hitachi.com> <550D962E.7010400@plumgrid.com> <550E9421.7030507@hitachi.com> In-Reply-To: <550E9421.7030507@hitachi.com> Content-Type: text/plain; charset=iso-2022-jp Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/22/15 3:06 AM, Masami Hiramatsu wrote: > (2015/03/22 1:02), Alexei Starovoitov wrote: >> On 3/21/15 5:14 AM, Masami Hiramatsu wrote: >>> (2015/03/21 8:30), Alexei Starovoitov wrote: >>>> >>>> Note, kprobes are _not_ a stable kernel ABI, so bpf programs attached to >>>> kprobes must be recompiled for every kernel version and user must supply correct >>>> LINUX_VERSION_CODE in attr.kern_version during bpf_prog_load() call. >>>> >>> >>> Would you mean that the ABI of kprobe-based BPF programs? Kprobe API/ABIs >>> (register_kprobe() etc.) are stable, but the code who use kprobes certainly >>> depends the kernel binary by design. So, if you meant it, BPF programs must >>> be recompiled for every kernel binaries (including configuration changes, >>> not only its version). >> >> yes. I mainly meant that bpf+kprobe programs must be recompiled >> for every kernel binary. > > Hmm, if so, as we do in perf (and systemtap too), you'd better check > kernel's build-id instead of the kernel version when loading the > BPF program. It is safer than the KERNEL_VERSION_CODE. It's not about safety. As I mentioned in cover letter: "version check is not used for safety, but for enforcing 'non-ABI-ness'" In other words it's like check-box next to 'terms and conditions' paragraph that the user has to click before he can continue. By providing 'kern_version' during loading the user accepts the fact that bpf+kprobe is not a stable ABI. Nothing more and nothing less. build-id cannot achieve that, because it cannot be checked from inside the kernel. User space tools that will compile ktap/dtrace scripts into bpf might use build-id for their own purpose, but that's a different discussion.