From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752634AbdIVW2y (ORCPT ); Fri, 22 Sep 2017 18:28:54 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43406 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752322AbdIVW2w (ORCPT ); Fri, 22 Sep 2017 18:28:52 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 8F409461C1 Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=jpoimboe@redhat.com Date: Fri, 22 Sep 2017 17:28:50 -0500 From: Josh Poimboeuf To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, ngo Molnar , Andrew Morton , "Paul E. McKenney" , stable@vger.kernel.org Subject: Re: [PATCH 3/4] extable: Enable RCU if it is not watching in kernel_text_address() Message-ID: <20170922222850.euysbk7fregluujg@treble> References: <20170922221543.900812109@goodmis.org> <20170922221837.736806508@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170922221837.736806508@goodmis.org> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Fri, 22 Sep 2017 22:28:52 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 22, 2017 at 06:15:46PM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" > > If kernel_text_address() is called when RCU is not watching, it can cause an > RCU bug because is_module_text_address() and the is_kprobe_*insn_slot() > functions require the use of RCU. is_bpf_text_address() also requires RCU. > Only enable RCU if it is not currently watching before it calls > is_module_text_address(). The use of rcu_nmi_enter() is used to enable RCU > because kernel_text_address() can happen pretty much anywhere (like an NMI), > and even from within an NMI. It is called via save_stack_trace() that can be > called by any WARN() or tracing function, which can happen while RCU is not > watching (for example, going to or coming from idle, or during CPU take down > or bring up). > > Cc: Paul E. McKenney > Cc: stable@vger.kernel.org > Fixes: 0be964be0 ("module: Sanitize RCU usage and locking") > Signed-off-by: Steven Rostedt (VMware) > --- > kernel/extable.c | 35 ++++++++++++++++++++++++++++++----- > 1 file changed, 30 insertions(+), 5 deletions(-) > > diff --git a/kernel/extable.c b/kernel/extable.c > index a7024a494faf..89c4668376a6 100644 > --- a/kernel/extable.c > +++ b/kernel/extable.c > @@ -119,17 +119,42 @@ int __kernel_text_address(unsigned long addr) > > int kernel_text_address(unsigned long addr) > { > + bool no_rcu; > + int ret = 1; > + > if (core_kernel_text(addr)) > return 1; > + > + /* > + * If a stack dump happens while RCU is not watching, then > + * RCU needs to be notified that it requires to start > + * watching again. This can happen either by tracing that > + * triggers a stack trace, or a WARN() that happens during > + * coming back from idle, or cpu on or offlining. > + * > + * is_module_text_address() as well as the kprobe slots > + * require RCU to be watching. Ditto here. -- Josh