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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 3DB9BC43612 for ; Wed, 9 Jan 2019 04:38:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0D03E21726 for ; Wed, 9 Jan 2019 04:38:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547008684; bh=ZozZl8PTh/RGHKwP46SOEn3tX4THFWGMVHsPm2As5fU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=swF3CjjBEOYvF7WWJb+CtrQsf10zS59FZ1kwIqhdKxuGBNe4lYIkXUkzyvzbI+rNl MfXGiF3/o5Xs4+pDBUd5U0chhQ4b0pkfKYv2agyrwMJbOnZt5utdkXRe7Wp6yue882 rc3ieh2KB7BADxnLvktyCr5YwIU2HgrGSlJnmCPE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729172AbfAIEiD (ORCPT ); Tue, 8 Jan 2019 23:38:03 -0500 Received: from mail.kernel.org ([198.145.29.99]:42340 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727947AbfAIEiC (ORCPT ); Tue, 8 Jan 2019 23:38:02 -0500 Received: from devnote (p103030-mobac01.tokyo.ocn.ne.jp [153.233.94.30]) (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 1997920665; Wed, 9 Jan 2019 04:37:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547008681; bh=ZozZl8PTh/RGHKwP46SOEn3tX4THFWGMVHsPm2As5fU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=BJUad3tJpcoX5MPbc2ssocRy0yLXmKbM1YQilBHCm8j47hYsKSGNKZs9MDy0DU7Cx ooffEmL/OWYor6HENOZnIXqNiIkwzGuGYp4AIJ4ITpYVKzAGvx366gxVMEb5nfxXv0 JSpLklxZsG1TDTKicfOh+u6hAMv4j5ShW8G6owFU= Date: Wed, 9 Jan 2019 13:37:57 +0900 From: Masami Hiramatsu To: Andrea Righi Cc: Ingo Molnar , peterz@infradead.org, Mathieu Desnoyers , linux-kernel , Steven Rostedt , stable@vger.kernel.org Subject: Re: [PATCH v2 0/3] kprobes: Fix kretprobe issues Message-Id: <20190109133757.8b28753d301f9d5378916438@kernel.org> In-Reply-To: <20190108103101.GE5966@xps-13> References: <154692263564.1133.17363562046971295490.stgit@devbox> <20190108103101.GE5966@xps-13> X-Mailer: Sylpheed 3.5.0 (GTK+ 2.24.30; 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 8 Jan 2019 11:31:01 +0100 Andrea Righi wrote: > On Tue, Jan 08, 2019 at 01:43:55PM +0900, Masami Hiramatsu wrote: > > Hello, > > > > This is v2 series of fixing kretprobe incorrect stacking order patches. > > In this version, I fixed a lack of kprobes.h including and added new > > patch for kretprobe trampoline recursion issue. (and add Cc:stable) > > > > (1) kprobe incorrct stacking order problem > > > > On recent talk with Andrea, I started more precise investigation on > > the kernel panic with kretprobes on notrace functions, which Francis > > had been reported last year ( https://lkml.org/lkml/2017/7/14/466 ). > > > > See the investigation details in > > https://lkml.kernel.org/r/154686789378.15479.2886543882215785247.stgit@devbox > > > > When we put a kretprobe on ftrace_ops_assist_func() and put another > > kretprobe on probed-function, below happens > > > > > > -> > > ->fentry > > ->ftrace_ops_assist_func() > > ->int3 > > ->kprobe_int3_handler() > > ...->pre_handler_kretprobe() > > push the return address (*fentry*) of ftrace_ops_assist_func() to > > top of the kretprobe list and replace it with kretprobe_trampoline. > > <-kprobe_int3_handler() > > <-(int3) > > ->kprobe_ftrace_handler() > > ...->pre_handler_kretprobe() > > push the return address (caller) of probed-function to top of the > > kretprobe list and replace it with kretprobe_trampoline. > > <-(kprobe_ftrace_handler()) > > <-(ftrace_ops_assist_func()) > > [kretprobe_trampoline] > > ->tampoline_handler() > > pop the return address (caller) from top of the kretprobe list > > <-(trampoline_handler()) > > > > [run caller with incorrect stack information] > > <-() > > !!KERNEL PANIC!! > > > > Therefore, this kernel panic happens only when we put 2 k*ret*probes on > > ftrace_ops_assist_func() and other functions. If we put kprobes, it > > doesn't cause any issue, since it doesn't change the return address. > > > > To fix (or just avoid) this issue, we can introduce a frame pointer > > verification to skip wrong order entries. And I also would like to > > blacklist those functions because those are part of ftrace-based > > kprobe handling routine. > > > > (2) kretprobe trampoline recursion problem > > > > This was found by Andrea in the previous thread > > https://lkml.kernel.org/r/20190107183444.GA5966@xps-13 > > > > ---- > > echo "r:event_1 __fdget" >> kprobe_events > > echo "r:event_2 _raw_spin_lock_irqsave" >> kprobe_events > > echo 1 > events/kprobes/enable > > [DEADLOCK] > > ---- > > > > Because kretprobe trampoline_handler uses spinlock for protecting > > hash table, if we probe the spinlock itself, it causes deadlock. > > Thank you Andrea and Steve for discovering this root cause!! > > > > This bug has been introduced with the asm-coded trampoline > > code, since previously it used another kprobe for hooking > > the function return placeholder (which only has a nop) and > > trampoline handler was called from that kprobe. > > > > To fix this bug, I introduced a dummy kprobe and set it in > > current_kprobe as we did in old days. > > > > Thank you, > > It looks all good to me, with this patch set I couldn't break the > kernel in any way. > > Tested-by: Andrea Righi Thank you, Andrea! Ingo, could you pick this series? -- Masami Hiramatsu