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List:       bugtraq
Subject:    Re: http://www.smashguard.org
From:       Pavel Machek <pavel () ucw ! cz>
Date:       2004-04-29 23:29:21
Message-ID: 20040429232921.GD8232 () elf ! ucw ! cz
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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
-- 
934a471f20d6580d5aad759bf0d97ddc
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