From: Vangelis <vangelis@qnis.net>
Date: Thu, 19 Dec 1996 18:58:39 -0800 (PST)
To: Peter Hendrickson <ph@netcom.com>
Subject: Re: Code+Data separation
In-Reply-To: <v02140b01aedf4fba9ec3@[192.0.2.1]>
Message-ID: <32B9F4F9.7174@qnis.net>
MIME-Version: 1.0
Content-Type: text/plain


Peter Hendrickson wrote:
> Are there any modern processors which keep the code and data separated?

I dunno about processors which make that distinction, but it can be done
in software using page-protection features of the Intel CPU.  Under DPMI
for DOS and I would think somehow under Windows, the DATA segment can be
specified as loading into a seperate page/selector from the code (Im a
little hazy on the specifics), and that page then marked essentially as
"read only".

I think this was designed to make software more crash-resistant though,
not hack-resistance.  There's probably many ways to circumvent this
(explicity changing the access to that page, tricking the VMM into
swapping that page out to disk, then editting the swap file while it's
out there, etc).
-- 
Vangelis <vangelis@qnis.net> /\oo/\
Finger for public key. PGP KeyID 1024/A558B025
PGP Fingerprint AE E0 BE 68 EE 7B CF 04  02 97 02 86 F0 C7 69 25
Life is my religion, the world is my altar.