From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752654AbdIVWoL (ORCPT ); Fri, 22 Sep 2017 18:44:11 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:33268 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752184AbdIVWoJ (ORCPT ); Fri, 22 Sep 2017 18:44:09 -0400 Date: Fri, 22 Sep 2017 15:44:06 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, ngo Molnar , Andrew Morton , stable@vger.kernel.org Subject: Re: [PATCH 3/4] extable: Enable RCU if it is not watching in kernel_text_address() Reply-To: paulmck@linux.vnet.ibm.com References: <20170922221543.900812109@goodmis.org> <20170922221837.736806508@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170922221837.736806508@goodmis.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17092222-2213-0000-0000-0000021FBA01 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007780; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000231; SDB=6.00920909; UDB=6.00462784; IPR=6.00701130; BA=6.00005601; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017252; XFM=3.00000015; UTC=2017-09-22 22:44:06 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17092222-2214-0000-0000-000057A218AF Message-Id: <20170922224406.GZ3521@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-09-22_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1709220318 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. > > 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 Do we need something calling out the dependency on the first two patches, or is that implied these days? > Fixes: 0be964be0 ("module: Sanitize RCU usage and locking") > Signed-off-by: Steven Rostedt (VMware) Give or take Josh's feedback on the commit log and comment: Acked-by: Paul E. McKenney > --- > 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. > + */ > + no_rcu = !rcu_is_watching(); > + > + /* Treat this like an NMI as it can happen anywhere */ > + if (no_rcu) > + rcu_nmi_enter(); > + > if (is_module_text_address(addr)) > - return 1; > + goto out; > if (is_ftrace_trampoline(addr)) > - return 1; > + goto out; > if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr)) > - return 1; > + goto out; > if (is_bpf_text_address(addr)) > - return 1; > - return 0; > + goto out; > + ret = 0; > +out: > + if (no_rcu) > + rcu_nmi_exit(); > + > + return ret; > } > > /* > -- > 2.13.2 > >