Subject: Re: using segmentation in the kernel
From: Arjan van de Ven <arjan@infradead.org>
To: Alon Bar-Lev <alon.barlev@gmail.com>
Cc: Brian Gerst <bgerst@didntduck.org>,
       "Jonathan M. McCune" <jonmccune@cmu.edu>, linux-kernel@vger.kernel.org,
       Arvind Seshadri <arvinds@cs.cmu.edu>, Bryan Parno <parno@cmu.edu>
In-Reply-To: <434C1F8E.6080405@gmail.com>
References: <434C1D60.2090901@cmu.edu> <434C2269.5090209@didntduck.org>
	 <434C1F8E.6080405@gmail.com>
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Date: Wed, 12 Oct 2005 11:05:35 +0200
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On Tue, 2005-10-11 at 22:24 +0200, Alon Bar-Lev wrote:
> Brian Gerst wrote:
> > Jonathan M. McCune wrote:
> > 
> >> Hello,
> >>
> > Why send the kernel back to the 2.0 days?  There is no valid reason for 
> > doing this with they way x86 segmentation works, which is why it was 
> > done away with in 2.1.
> > 
> 
> But with segmentation you can set code to be read-only, 

you can do that without segmentation too, absolutely no problem

> disallow execution from stack,

That is why CPUs have NX nowadays. And it's not like the kernel is full
of buffer overflows; due to the 4Kb stack space (total), there are very
very few static buffers on the stack at all; simply because theres no
space to do it.

>  separate modules so that they 
> will not affect kernel and more...

and I don't believe this one yota. THe only way to do this is to run
modules in ring 1, at which point you are in deep shit anyway.


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