[34748] in bugtraq
Re: http://www.smashguard.org
daemon@ATHENA.MIT.EDU (Pavel Machek)
Fri Apr 30 20:56:52 2004
Date: Fri, 30 Apr 2004 01:29:21 +0200
From: Pavel Machek <pavel@ucw.cz>
To: Crispin Cowan <crispin@immunix.com>
Cc: Hilmi Ozdoganoglu <cyprian@purdue.edu>, Dave Paris <dparis@w3works.com>,
bugtraq@securityfocus.com
Message-ID: <20040429232921.GD8232@elf.ucw.cz>
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In-Reply-To: <40918E98.8080502@immunix.com>
Hi!
> >>>Computer World, January 15, 2004).
> >>>
> >>>
> >>>
> >>As Theo said, the AMD buffer overflow "protection" is nothing more than
> >>sensible separation of R and X bits per page, fixing a glaring and
> >>
> >>
> >
> >Actually it is not "sensible", and it is not separation.
> >
> >You can have r--, r-x, but you can't have --x.
> >
> >
> But that is *exactly* what is meant by "separation" of R and X.
>
> I have no idea what you mean by it not being "sensible". Most every CPU
> I have ever seen does this except the x86. Someone apparently thought
> there was no value in separate R and X bits for the i386 back in the
> mid-80s. It was a false economy :)
Well.. they are not really separate bits.
If they was, you'd have ---, --x, r--, r-x. You can't have --x
combination (which is sad for the emulators).
I believe that on most sane architectures (m68k at least), you can
have all 4 combinations.
Pavel
--
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