Re: using segmentation in the kernel

[Brian Gerst]

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, disallow 
> execution from stack, separate modules so that they will not affect 
> kernel and more...
>
> The main problem with segmentation is that it is x86 specific...

Too much pain for for not enough gain.  Segments are not fine-grained 
enough to work well.  Look at the PaX and execshield hacks for 
userspace.  You are far better off working at the page-table level (RO 
and NX pages) which has the advantage of being portable.

--
				Brian Gerst
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