Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754952AbXEBKGV (ORCPT ); Wed, 2 May 2007 06:06:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754961AbXEBKGV (ORCPT ); Wed, 2 May 2007 06:06:21 -0400 Received: from rgminet01.oracle.com ([148.87.113.118]:31280 "EHLO rgminet01.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754457AbXEBKGU (ORCPT ); Wed, 2 May 2007 06:06:20 -0400 Date: Wed, 2 May 2007 03:06:00 -0700 From: Bill Irwin To: Andrew Morton Cc: Bill Irwin , Dan Kruchinin , linux-kernel@vger.kernel.org, Jeremy Fitzhardinge , Andi Kleen , Ingo Molnar , wli@holomorphy.com Subject: Re: [RFC BUG?] dereference PAGE_OFFSET address (rc7-mm2) Message-ID: <20070502100600.GZ26598@holomorphy.com> Mail-Followup-To: Bill Irwin , Andrew Morton , Dan Kruchinin , linux-kernel@vger.kernel.org, Jeremy Fitzhardinge , Andi Kleen , Ingo Molnar References: <20070502005140.b94500ff.akpm@linux-foundation.org> <20070502084617.GY26598@holomorphy.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070502084617.GY26598@holomorphy.com> User-Agent: Mutt/1.5.11 X-Brightmail-Tracker: AAAAAQAAAAI= X-Brightmail-Tracker: AAAAAQAAAAI= X-Whitelist: TRUE X-Whitelist: TRUE Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1221 Lines: 27 On Wed, May 02, 2007 at 12:51:40AM -0700, Andrew Morton wrote: >> Thanks for the report. I can reproduce it. >> Bisection shows that x86_64-mm-paravirt-initial-pagetable.patch caused >> this. >> I didn't check whether the patch actually permits us to read kernel >> memory. Probably it does. Probably we'd prefer that it didn't ;) On Wed, May 02, 2007 at 01:46:17AM -0700, Bill Irwin wrote: > Brown paper bag time. I don't know how it got past me. Brain dump before crashing for the night: The patch refuses to clobber already-present pagetable entries of whatever origin. There are pagetables prior to this setup covering the address range just above PAGE_OFFSET. If this theory is correct, you should only be able to go a few MB above PAGE_OFFSET before encountering unreadable kernel memory. IIRC those pagetables are a statically allocated array in assembly; altering that array to set supervisor bits may resolve it, though it may also be freed as initmem. -- wli - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/