Bugtraq: Re: http://www.smashguard.org

[Pavel Machek <pavel () ucw cz>]

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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