Date: Thu, 18 May 2000 15:33:30 -0400 (EDT) From: John Baldwin <jhb@FreeBSD.org> To: Olaf Hoyer <ohoyer@fbwi.fh-wilhelmshaven.de> Cc: chat@FreeBSD.ORG Subject: RE: Fwd: Is this a joke? Message-ID: <20000518193245.ULAE22611.mail.rdc1.va.home.com@john.baldwin.cx> In-Reply-To: <4.1.20000518203632.009d3be0@mail.rz.fh-wilhelmshaven.de>
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On 18-May-00 Olaf Hoyer wrote: > Hi! > > This is going around on some lists, maybe someone could comment on this, if > there is a remote possibility about that? This looks rather rediculous, actually. > Regards > Olaf Hoyer > >>>From: Fred Cohen <fc@all.net> >>>MIME-Version: 1.0 >>>Mailing-List: list iwar@egroups.com; contact iwar-owner@egroups.com >>>Delivered-To: mailing list iwar@egroups.com >>>Precedence: bulk >>>List-Unsubscribe: <mailto:iwar-unsubscribe@egroups.com> >>>Date: Mon, 15 May 2000 20:53:44 -0700 (PDT) >>>Reply-To: iwar@egroups.com >>>Subject: [iwar] News >>>Status: RO >>> >>>Here's something I heard today - from a very reliable source: >>> >>>In order to allow application programs to access the display memory >>>without operating system intervention, an undocumented hardware >>>instruction on Pentium class Intel processors and possibly other >>>'compatable' processor architectures has been included to grant >>>user-level processes direct access to the real memory of the central >>>processor. This means that a user process can read directly from or >>>write directly to system memory. the net effect is that any user who >>>can run a program of their devising on one of these computers is >>>guaranteed to be able to take over the system and do whatever they wish >>>- regardless of the operating system - and regardless of any add-on >>>precautions at the software level. Well, for one thing, apart from registers, there is no 'real memory of the system processor'. Every process reads and writes to memory. Probably what they are trying to refer to is that this mysterious instruction allows you to bypass the paging and protection mechanisms and specify a direct physical address. This really wouldn't do you much good unless you had initimate knowledge of the memory organization of the underlying operating system. However, the closest thing to this mystery instruction that I can think of is the 'umov' instruction, which is used in coordination with ICE's to allow you to access the main "user" memory of the system when you are running in the context of the ICE (which has its own memory and memory address space). Also, the poor grammar and general vagueness of this message leave me very suspicious. I wouldn't put much stock in this claim, personally. > Olaf Hoyer www.nightfire.de mailto:Olaf.Hoyer@nightfire.de > FreeBSD- Turning PC's into workstations ICQ:22838075 -- John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/ PGP Key: http://www.cslab.vt.edu/~jobaldwi/pgpkey.asc "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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