From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 18 Jun 2002 14:35:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 18 Jun 2002 14:35:14 -0400 Received: from web12302.mail.yahoo.com ([216.136.173.100]:18037 "HELO web12302.mail.yahoo.com") by vger.kernel.org with SMTP id ; Tue, 18 Jun 2002 14:35:13 -0400 Message-ID: <20020618183515.13963.qmail@web12302.mail.yahoo.com> Date: Tue, 18 Jun 2002 11:35:15 -0700 (PDT) From: Myrddin Ambrosius Subject: Re: Drivers, Hardware, and their relationship to Bagels. To: root@chaos.analogic.com Cc: linux-kernel@vger.kernel.org In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --- "Richard B. Johnson" wrote: > No hole you can drive through. A process with a UID > of 0 and > a GID of 0 can do anything it wants. It can execute > iopl(3) > and set an I/O permission level that allows it to > directly access > hardware I/O ports, etc. It can also turn off > interrupts. Basically, > it can do anything, since such a process can also > memory-map anything. But since it is the kernel that permits that (by definition, since somebody has to check the UID & GID! :) then the kernel can also restrict that. The system admin account (UID/GID 0) could just as easily access a virtual memory map, virtual I/O ports, etc, with the kernel then handling how that maps onto the physical world, and even IF it does. > Users are not supposed to execute as 'root'. Also, > only certain > priviliged tasks execute as root. Ignore that this The problem with priviliged tasks is that (in general) they run with absolute privilige. Sure, some of these priviliges can be turned off, but if /dev/mem is reachable, then they can be turned back on again, precicely for the reasons you give. I guess that my understanding for having kernels the size and complexity of Linux, as opposed to, say, CP/M, is that the kernel can reduce the need for userspace apps to have dangerous powers. __________________________________________________ Do You Yahoo!? Yahoo! - Official partner of 2002 FIFA World Cup http://fifaworldcup.yahoo.com