RE: gate page oops

From: Jason Baron <jbaron_at_redhat.com>
Date: 2005-05-04 06:47:47
On Fri, 29 Apr 2005, David Mosberger wrote:

> >>>>> On Tue, 26 Apr 2005 13:10:06 -0400 (EDT), Jason Baron <jbaron@redhat.com> said:
> 
>   Jason> On Fri, 22 Apr 2005, Luck, Tony wrote:
> 
>   >> The gate page only needs to be PAGE_SIZE ... doesn't it?
> 
>   Jason> I'm not really sure...i was hoping somebody on the list would
>   Jason> know :) If you look at setup_gate(), it establishes two gate
>   Jason> pages, the comment says:
> 
>   Jason> * Map the gate page twice: once read-only to export the ELF
>   Jason> headers etc. and once * execute-only page to enable
>   Jason> privilege-promotion via "epc":
> 
>   Jason> So the patch i proposed was intended to allow user access to
>   Jason> these two regions. Currently, that isn't being done properly,
>   Jason> leading to an oops.
> 
> Yes, IIRC, we need to give ptrace() access to the execute-only page so
> that a debugger can read and decode the instruction at the address
> (yes, that circumvents the execute-only part of the mapping, but we
> don't really care about that; the only reason it's execute-only is
> because that's the only way to get the promote-privilege-on-epc
> behavior).
> 
> 	--david
> 

So are there any objections to the patch? It seems to be consistent with 
this, and it fixes a local DOS.

thanks,

-Jason
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Received on Tue May 3 16:47:59 2005

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