RE: gate page oops

From: David Mosberger <davidm_at_napali.hpl.hp.com>
Date: 2005-04-29 21:42:08
>>>>> 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
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Received on Fri Apr 29 07:42:23 2005

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