From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Mosberger Date: Fri, 29 Apr 2005 11:42:08 +0000 Subject: RE: gate page oops Message-Id: <17010.7568.775064.65612@napali.hpl.hp.com> List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org >>>>> On Tue, 26 Apr 2005 13:10:06 -0400 (EDT), Jason Baron 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