From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965640Ab0COSUa (ORCPT ); Mon, 15 Mar 2010 14:20:30 -0400 Received: from mail-bw0-f209.google.com ([209.85.218.209]:48019 "EHLO mail-bw0-f209.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965596Ab0COSU3 convert rfc822-to-8bit (ORCPT ); Mon, 15 Mar 2010 14:20:29 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=rsMAG6TBWH+Uh+DcAT8AO07JzHsdcQDrMt0WJDHFMFjwO4upKrYW/yBOY6junpXaU2 lJj/hXLu102nFkrlxy46fm9UmZyROtChBYGe9pSj8f85nVqQmsvwD6ZKhL37yCuVILHB sS/h44zlaZm54CtjZGyRR43ELs47LoV013Q6w= MIME-Version: 1.0 In-Reply-To: <4B9B812F.3030306@free.fr> References: <4B9B812F.3030306@free.fr> Date: Mon, 15 Mar 2010 14:20:24 -0400 Message-ID: <817ecb6f1003151120s3e6f34acl39563fc0dc8fa9db@mail.gmail.com> Subject: Re: [tip:x86/mm] x86, mm: NX protection for kernel data From: Siarhei Liakh To: matthieu castet Cc: Linux Kernel list , Ingo Molnar Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Mar 13, 2010 at 8:12 AM, matthieu castet wrote: > Hi, > >> > looking for c17ebdb8 in system.map points to a location in pgd_lock: >> > ============================================ >> > $grep c17ebd System.map >> > c17ebd68 d bios_check_work >> > c17ebda8 d highmem_pages >> > c17ebdac D pgd_lock >> > c17ebdc8 D pgd_list >> > c17ebdd0 D show_unhandled_signals >> > c17ebdd4 d cpa_lock >> > c17ebdf0 d memtype_lock >> > ============================================ >> > >> > I've looked at the lock debugging and could not find any place that >> > would look like an attempt to execute data. This would lead me to >> > think that calling set_memory_nx from kernel_init somehow confuses the >> > lock debugging subsystem, or set_memory_nx does not change page >> > attributes in a safe manner (for example when a lock is stored inside >> > the page whose attributes are being changed). >> >> I've done some extra debugging and it really does look like the crash >> happens when we are setting NX on a large page which has pgd_lock >> inside it. >> >> Here is a trace of printk's that I added to troubleshoot this issue: >> ========================= >> [    3.072003] try_preserve_large_page - enter >> [    3.073185] try_preserve_large_page - address: 0xc1600000 >> [    3.074513] try_preserve_large_page - 2M page >> [    3.075606] try_preserve_large_page - about to call static_protections >> [    3.076000] try_preserve_large_page - back from static_protections >> [    3.076000] try_preserve_large_page - past loop >> [    3.076000] try_preserve_large_page - new_prot != old_prot >> [    3.076000] try_preserve_large_page - the address is aligned and >> the number of pages covers the full range >> [    3.076000] try_preserve_large_page - about to call __set_pmd_pte >> [    3.076000] __set_pmd_pte - enter >> [    3.076000] __set_pmd_pte - address: 0xc1600000 >> [    3.076000] __set_pmd_pte - about to call >> set_pte_atomic(*0xc18c0058(low=0x16001e3, high=0x0), (low=0x16001e1, >> high=0x80000000)) >> [lock-up here] >> ========================= >> [...] > 0xc1600000 2MB page is in 0xc1600000-0xc1800000 range.  pgd_lock > (0xc17ebdac) seems to be in that range. That's what I was thinking... > You change attribute from (low=0x16001e3, high=0x0) to (low=0x16001e1, > high=0x80000000). IE you set > NX bit (bit 63), but you also clear R/W bit (bit 2). So the page become read > only, but you are using a lock > inside this page that need RW access. So you got a page fault. Yes, that would do it. > Now I don't know what should be done. > Is that normal we set the page RO ? No, this page should not be RO, as it contains kernel's RW data. The interesting part is that the call that initiates the change is set_memory_nx(), so it should not be clearing RW bit... The interesting part is that the kernel does not crash with lock debugging disabled. Thanks for your help.