Subject: Re: using segmentation in the kernel
From: Arjan van de Ven <arjan@infradead.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Alon Bar-Lev <alon.barlev@gmail.com>, 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>
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Date: Wed, 12 Oct 2005 17:44:33 +0200
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> > 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.
> 
> Not neccessarily. Its how Xen works on x86-32 for example. It keeps
> itself protected from the entire Linux instance by using segmentation on

it only works if you make a very small syscall-like area which you use
to talk to the "real" kernel. Which is entirely not how linux modules
work right now.... at which point you're just about a userspace
application anyway. Might be an interesting research project of
course...


> 32bit processors (not 64bit however as x86-64 has no segments in 64bit)

afaik x86-64 grew segments recently for 64 bit mode for an unnamed other
virtualization vendor


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