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From: jesse%altos.Altos.COM@vicom.com (Jesse Chisholm AAC-RJesseD)
Newsgroups: comp.virus
Subject: Re: MS-DOS in ROM (PC)
Message-ID: <0015.9106121957.AA12675@ubu.cert.sei.cmu.edu>
Date: 12 Jun 91 04:10:44 GMT
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padgett%tccslr.dnet@mmc.com (Padgett Peterson) writes:
| "William Walker C60223 x4570" <walker@aedc-vax.af.mil> writes:
|
| >We're writing from two different premises.  Padgett is writing about
| >MS- DOS actually running from ROM, while I'm writing about the DOS
| >files, and the boot disk itself, being in ROM ( a ROM-disk, as opposed
| >to a RAM-disk ).  ... The method of booting from
| >a ROM- disk ( with an infection-proof boot sector and system files ),
| >which I wrote about, is not implemented at this time, to the best of
| >my knowledge.

Acer America in joint venture with Smith Corona has recently marketed
a small 286 PC that has a ROM cartridge that is used as a ROM disk.
SCC sells it as a PWP-100 (Personal Word Processor) and the software
looks alot like their earlier WP machines.  This is the first in a
product line that has MS-DOS on ROM cartridge.  Not all of DOS, just
enough to boot. (IO.SYS, MSDOS.SYS, COMMAND.COM, AUTOEXEC.BAT,
CONFIG.SYS, and maybe SHARE.EXE, HIMEM.SYS, ANSI.SYS, ..., and the WP
software)

| While I follow the premise better now, what you are talking about is
| what I referred to in the third option - somehow swapping ROM
| addresses for RAM addresses or possibly a "page frame" approach such
| as used for expanded memory. It will take a special BIOS driver to
| accomodate just like a RAM-disk requires a special driver and the data
| areas will have to stay resident somewhere. The point is that there
| are a finite number of addresses available and if some are used for
| ROM then there are that many less for RAM unless some extra memory
| management scheme is used such as that used for "shadow RAM" on 386s -
| not difficult but requires a few extras.

Acer's method doesn't use up RAM addresses, since the ROM card is seen
as a read-only hard disk.  The ROM card itself does use some IOcard
address space since it is considered an expansion card by the
hardware.

| The point I was trying to make was that even with this type of
| mechanism, the same holes exist in MS-DOS as did before. Some have
| been moved (e.g.  the first attackable point) so that specific
| malicious software will be thwarted, but the hole still exists and
| will just be exploited in the next crop. There is still NO integrity
| management in MS-DOS.

Sad but true.

Jesse Chisholm          | Disclaimer: My opinions are rarely understood, let
jesse@altos86.altos.com | tel: 1-408-432-6200 | alone held, by this company.
jesse@gumby.altos.com   | fax: 1-408-435-8517 |-----------------------------
======== This company has officially disavowed all knowledge of my opinions.
- --
"Question Authority!"  -- Wallace Stegner
"And that's an order!"