Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753345AbdL1EQu (ORCPT ); Wed, 27 Dec 2017 23:16:50 -0500 Received: from mail.kernel.org ([198.145.29.99]:57316 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752840AbdL1EQs (ORCPT ); Wed, 27 Dec 2017 23:16:48 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E97322188F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=rostedt@goodmis.org Date: Wed, 27 Dec 2017 23:16:44 -0500 From: Steven Rostedt To: Alexei Starovoitov Cc: Masami Hiramatsu , Alexei Starovoitov , Josef Bacik , , , , , , , , , , Josef Bacik , Akinobu Mita Subject: Re: [RFC PATCH bpf-next v2 1/4] tracing/kprobe: bpf: Check error injectable event is on function entry Message-ID: <20171227231644.168abc0f@vmware.local.home> In-Reply-To: <03e0ebb7-0b2a-4235-3408-c0d59a1ba4c2@fb.com> References: <151427438796.32561.4235654585430455286.stgit@devbox> <151427441954.32561.8731119329264462024.stgit@devbox> <20171227015730.jjggymg4uqllteuy@ast-mbp> <20171227145628.53f68f391b2108d6df118ca7@kernel.org> <20171228113434.eb182c348fc69853fec934ee@kernel.org> <03e0ebb7-0b2a-4235-3408-c0d59a1ba4c2@fb.com> X-Mailer: Claws Mail 3.15.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1034 Lines: 24 On Wed, 27 Dec 2017 19:45:42 -0800 Alexei Starovoitov wrote: > I don't think that's the case. My reading of current > trace_kprobe_ftrace() -> arch_check_ftrace_location() > is that it will not be true for old mcount case. In the old mcount case, you can't use ftrace to return without calling the function. That is, no modification of the return ip, unless you created a trampoline that could handle arbitrary stack frames, and remove them from the stack before returning back to the function. > > As far as the rest of your arguments it very much puzzles me that > you claim that this patch suppose to work based on historical > reasoning whereas you did NOT test it. I believe that Masami is saying that the modification of the IP from kprobes has been very well tested. But I'm guessing that you still want a test case for using kprobes in this particular instance. It's not the implementation of modifying the IP that you are worried about, but the implementation of BPF using it in this case. Right? -- Steve