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, 21 Feb 2003 13:17:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 21 Feb 2003 13:17:39 -0500 Received: from vbws78.voicebs.com ([66.238.160.78]:6674 "EHLO quark.didntduck.org") by vger.kernel.org with ESMTP id ; Fri, 21 Feb 2003 13:17:38 -0500 Message-ID: <3E566F9C.7010406@didntduck.org> Date: Fri, 21 Feb 2003 13:27:40 -0500 From: Brian Gerst User-Agent: Mozilla/5.0 (Windows; U; WinNT4.0; en-US; rv:1.2.1) Gecko/20021130 X-Accept-Language: en-us, en MIME-Version: 1.0 To: nataraja kumar CC: linux-kernel@vger.kernel.org Subject: Re: A question on kernel stack References: <20030221180508.18214.qmail@web20206.mail.yahoo.com> In-Reply-To: <20030221180508.18214.qmail@web20206.mail.yahoo.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org nataraja kumar wrote: > hi, > my apologies if i am wrong. please let me know > why does kernel use kernel stack when process jumps > from user mode to kernel mode. why can't user stack > be used ? > > nattu. 1) The user stack could be invalid. An invalid stack in the kernel will cause the processor to double fault (see the recent double fault thread). 2) Security. You could set up the stack pointer from userspace so that the kernel would overwrite memory that userspace can't access. 3) Security #2. You don't want to give userspace access to certain data written to the stack in kernel mode. -- Brian Gerst