From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753570AbcFMEar (ORCPT ); Mon, 13 Jun 2016 00:30:47 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:43862 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750702AbcFMEap (ORCPT ); Mon, 13 Jun 2016 00:30:45 -0400 X-IBM-Helo: d03dlp03.boulder.ibm.com X-IBM-MailFrom: ananth@linux.vnet.ibm.com X-IBM-RcptTo: rostedt@goodmis.org;peterz@infradead.org;luto@kernel.org;mhiramat@kernel.org;tglx@linutronix.de;mingo@redhat.com;systemtap@sourceware.org;linux-kernel@vger.kernel.org;hpa@zytor.com Date: Mon, 13 Jun 2016 10:00:33 +0530 From: Ananth N Mavinakayanahalli To: Masami Hiramatsu Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Peter Zijlstra , Thomas Gleixner , "H . Peter Anvin" , Andy Lutomirski , systemtap@sourceware.org, Steven Rostedt Subject: Re: [PATCH tip/master] [BUGFIX] kprobes/x86: Fix to clear TF bit in fault-on-single-stepping Reply-To: ananth@linux.vnet.ibm.com References: <20160611140648.25885.37482.stgit@devbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160611140648.25885.37482.stgit@devbox> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16061304-0008-0000-0000-000004C9C680 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16061304-0009-0000-0000-000038532A46 Message-Id: <20160613043033.GA22985@in.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-06-13_02:,, 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=8.0.1-1604210000 definitions=main-1606130049 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jun 11, 2016 at 11:06:53PM +0900, Masami Hiramatsu wrote: > Fix kprobe_fault_handler to clear TF (trap flag) bit of > flags register in the case of fault fixup on single-stepping. > > If we put a kprobe on the instruction which can cause a > page fault (e.g. actual mov instructions in copy_user_*), > that fault happens on a single-stepping buffer. In this > case, kprobes resets running instance so that the CPU can > retry execution on the original ip address. > However, current code forgets reset TF bit. Since this > fault happens with TF bit set for enabling single-stepping, > when it retries, it causes a debug exception and kprobes > can not handle it because it already reset itself. > > On the most of x86-64 platform, it can be easily reproduced > by using kprobe tracer. E.g. > > # cd /sys/kernel/debug/tracing > # echo p copy_user_enhanced_fast_string+5 > kprobe_events > # echo 1 > events/kprobes/enable > > And you'll see a kernel panic on do_debug(), since the debug > trap is not handled by kprobes. > > To fix this problem, we just need to clear the TF bit when > resetting running kprobe. > > Signed-off-by: Masami Hiramatsu Good catch! Reviewed-by: Ananth N Mavinakayanahalli