From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 25 May 2001 08:07:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 25 May 2001 08:07:47 -0400 Received: from femail19.sdc1.sfba.home.com ([24.0.95.128]:55171 "EHLO femail19.sdc1.sfba.home.com") by vger.kernel.org with ESMTP id ; Fri, 25 May 2001 08:07:34 -0400 Message-ID: <3B0E4B0C.C5F3218F@didntduck.org> Date: Fri, 25 May 2001 08:07:40 -0400 From: Brian Gerst X-Mailer: Mozilla 4.76 [en] (X11; U; Linux 2.4.5-pre3 i686) X-Accept-Language: en MIME-Version: 1.0 To: Andi Kleen CC: linux-kernel@vger.kernel.org Subject: Re: [CHECKER] large stack variables (>=1K) in 2.4.4 and 2.4.4-ac8 In-Reply-To: <200105242110.OAA29766@csl.Stanford.EDU> <200105242308.f4ON8fv8015978@webber.adilger.int> <20010525013303.A21810@gruyere.muc.suse.de> <3B0E4762.7A7A3818@didntduck.org> <20010525135317.B29643@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 Fri, May 25, 2001 at 07:52:02AM -0400, Brian Gerst wrote: > > Actually, you will never get a stack fault exception, since with a flat > > stack segment you can never get a limit violation. All you will do is > > corrupt the data in task struct and cause an oops later on when the > > kernel tries to use the task struct. There are only two ways to > > properly trap a kernel stack overflow: > > In my experience the stack pointer eventually gets corrupted and starts > pointing to some unmapped area, which gives you a stack fault (admittedly > a backtrace is a bit hard after that) You mean a double fault. #SS is only called when there is a limit violation on the stack segment or the stack segment is not present. I guess you could get a limit violation if it tried to wrap around below 0, but you would get a page fault first. An unmapped page will always cause a page fault, but since the stack is still invalid, it would then cause a double fault. -- Brian Gerst