From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 22 Aug 2001 08:15:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 22 Aug 2001 08:14:57 -0400 Received: from femail25.sdc1.sfba.home.com ([24.254.60.15]:27299 "EHLO femail25.sdc1.sfba.home.com") by vger.kernel.org with ESMTP id ; Wed, 22 Aug 2001 08:14:44 -0400 Message-ID: <3B83A17C.CB8ABC53@didntduck.org> Date: Wed, 22 Aug 2001 08:11:40 -0400 From: Brian Gerst X-Mailer: Mozilla 4.76 [en] (X11; U; Linux 2.4.9-pre4 i686) X-Accept-Language: en MIME-Version: 1.0 To: Andi Kleen CC: linux-kernel@vger.kernel.org, set@pobox.com, alan@lxorguk.ukuu.org.uk, Wilfried.Weissmann@gmx.at Subject: Re: [OOPS] repeatable 2.4.8-ac7, 2.4.7-ac6 just run xdos In-Reply-To: <20010819004703.A226@squish.home.loc.suse.lists.linux.kernel> <3B831CDF.4CC930A7@didntduck.org.suse.lists.linux.kernel> <3B839E47.874F8F64@didntduck.org> <20010822141058.A18043@gruyere.muc.suse.de> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andi Kleen wrote: > > On Wed, Aug 22, 2001 at 07:57:59AM -0400, Brian Gerst wrote: > > Yes. What happened here is that %ds and %es were not being updated > > atomically. Under normal operation, this would just leave %es with > > USER_DS, which is sufficiently equivalent to KERNEL_DS to not cause a > > fault. Coming out of vm86 mode however forces the data segment > > registers to null after saving the real mode values on the stack. If an > > interrupt happened between setting %ds and %es (what are the odds?) then > > that assumption would fail and leave %es null, causing the next string > > instruction to go boom. The same fix should be applied to entry.S as > > well. > > No that's not the problem. interrupt gates come in with interrupts off, > so there are no other interrupts that could race here. The syscall entry > always updates %ds/%es unconditionally and %ds first, so there is no > race. > > It was much simpler. It assumed that __KERNEL_DS could not be loaded > from user space because of the segment register priviledge checking; and > that was obviously not true from vm86 mode. > > -Andi The kernel was initially entered throught the general protection fault trap gate, with interupts on. The syscall entry was left on the stack because of the way sys_vm86 works. -- Brian Gerst