From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755326Ab2B0Vaw (ORCPT ); Mon, 27 Feb 2012 16:30:52 -0500 Received: from mail-pz0-f46.google.com ([209.85.210.46]:39804 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753689Ab2B0Vau (ORCPT ); Mon, 27 Feb 2012 16:30:50 -0500 Authentication-Results: mr.google.com; spf=pass (google.com: domain of gregkh@linuxfoundation.org designates 10.68.219.232 as permitted sender) smtp.mail=gregkh@linuxfoundation.org Date: Mon, 27 Feb 2012 13:29:47 -0800 From: Greg KH To: Steven Rostedt Cc: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, torvalds@linux-foundation.org, stable@kernel.org, tglx@linutronix.de, mingo@elte.hu, linux-tip-commits@vger.kernel.org Subject: Re: [tip:x86/urgent] x86/nmi: Test saved %cs in NMI to determine nested NMI case Message-ID: <20120227212947.GA3002@kroah.com> References: <1329687817.1561.27.camel@acer.local.home> <1329756701.25686.31.camel@gandalf.stny.rr.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1329756701.25686.31.camel@gandalf.stny.rr.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 20, 2012 at 11:51:41AM -0500, Steven Rostedt wrote: > On Mon, 2012-02-20 at 03:47 -0800, tip-bot for Steven Rostedt wrote: > > Commit-ID: 45d5a1683c04be28abdf5c04c27b1417e0374486 > > Gitweb: http://git.kernel.org/tip/45d5a1683c04be28abdf5c04c27b1417e0374486 > > Author: Steven Rostedt > > AuthorDate: Sun, 19 Feb 2012 16:43:37 -0500 > > Committer: Ingo Molnar > > CommitDate: Mon, 20 Feb 2012 09:09:57 +0100 > > > > x86/nmi: Test saved %cs in NMI to determine nested NMI case > > > > Currently, the NMI handler tests if it is nested by checking the > > special variable saved on the stack (set during NMI handling) > > and whether the saved stack is the NMI stack as well (to prevent > > the race when the variable is set to zero). > > > > But userspace may set their %rsp to any value as long as they do > > not derefence it, and it may make it point to the NMI stack, > > which will prevent NMIs from triggering while the userspace app > > is running. (I tested this, and it is indeed the case) > > > > Add another check to determine nested NMIs by looking at the > > saved %cs (code segment register) and making sure that it is the > > kernel code segment. > > > > Signed-off-by: Steven Rostedt > > Cc: H. Peter Anvin > > Cc: Peter Zijlstra > > Cc: Linus Torvalds > > Cc: > > Just so that we do not confuse Greg, the bug was introduced in the 3.3 > merge window. It does not exist in 3.2 or earlier. Thanks for letting me know, I would have been confused :) greg k-h