From: ao950 AT FreeNet DOT Carleton DOT CA (Paul Derbyshire)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Ring 0?
Date: 10 Mar 1997 05:31:11 GMT
Organization: The National Capital FreeNet
Lines: 28
Message-ID: <5g06av$qit@freenet-news.carleton.ca>
References: <5fivnk$cfc AT freenet-news DOT carleton DOT ca> <5fte3k$h5h AT freenet-news DOT carleton DOT ca> <33235B3D DOT 681C AT cs DOT com>
Reply-To: ao950 AT FreeNet DOT Carleton DOT CA (Paul Derbyshire)
NNTP-Posting-Host: freenet2.carleton.ca
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp


"John M. Aldrich" (fighteer AT cs DOT com) writes:
> Paul Derbyshire wrote:
>> 
>> As for a ring 3 program being unable to currupt the kernel, I'm not sure
>> this is entirely correct. I discovered that a DOS program running in a DOS
>> box under Win 95 (and DOS boxes presumably run in ring 3) can crash the
>> machine with a bad memory write.
> 
> All DOS programs are not DPMI programs.  Real-mode code that runs in a
> DOS box will completely ignore the memory manager and can go ahead and
> corrupt anything it likes.  Usually, Win95 will catch the program at it,
> but it can still take down your computer.

Flame me if I'm wrong, but doesn't a DOS box run on a virtual machine with
its own Windows-provided image of the real memory map? Aren't all of its
transactions indirect via the Windows kernel then?

[DOS is terribly insecure]

Is this caused by an aspect of Intel CPU design or by an aspect of the
DPMI spec?

--
    .*.  Where feelings are concerned, answers are rarely simple [GeneDeWeese]
 -()  <  When I go to the theater, I always go straight to the "bag and mix"
    `*'  bulk candy section...because variety is the spice of life... [me]
Paul Derbyshire ao950 AT freenet DOT carleton DOT ca, http://chat.carleton.ca/~pderbysh