From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754016Ab1ATTJF (ORCPT ); Thu, 20 Jan 2011 14:09:05 -0500 Received: from rcsinet10.oracle.com ([148.87.113.121]:43959 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752903Ab1ATTIm convert rfc822-to-8bit (ORCPT >); Thu, 20 Jan 2011 14:08:42 -0500 Date: Thu, 20 Jan 2011 14:05:31 -0500 From: Konrad Rzeszutek Wilk To: Ian Campbell Cc: "castet.matthieu@free.fr" , Kees Cook , Jeremy Fitzhardinge , "keir.fraser@eu.citrix.com" , "mingo@redhat.com" , "hpa@zytor.com" , "sliakh.lkml@gmail.com" , "jmorris@namei.org" , "linux-kernel@vger.kernel.org" , "rusty@rustcorp.com.au" , "torvalds@linux-foundation.org" , "ak@muc.de" , "davej@redhat.com" , "jiang@cs.ncsu.edu" , "arjan@infradead.org" , "tglx@linutronix.de" , "sfr@canb.auug.org.au" , "mingo@elte.hu" , Stefan Bader Subject: Re: [tip:x86/security] x86: Add NX protection for kernel data Message-ID: <20110120190531.GA9687@dumpdata.com> References: <4CE2F82E.60601@free.fr> <20110111233135.GL4979@outflux.net> <20110114201530.GA14339@dumpdata.com> <20110119211432.GA20535@dumpdata.com> <20110119235957.6ea35dc8@mat-laptop> <20110119233824.GA2869@dumpdata.com> <1295522306.4d381a02b1e10@imp.free.fr> <20110120150618.GC5092@dumpdata.com> <1295537856.14780.54.camel@zakaz.uk.xensource.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1295537856.14780.54.camel@zakaz.uk.xensource.com> User-Agent: Mutt/1.5.20 (2009-06-14) Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 20, 2011 at 03:37:36PM +0000, Ian Campbell wrote: > On Thu, 2011-01-20 at 15:06 +0000, Konrad Rzeszutek Wilk wrote: > > On Thu, Jan 20, 2011 at 12:18:26PM +0100, castet.matthieu@free.fr wrote: > > > Quoting Konrad Rzeszutek Wilk : > > > > > > > On Wed, Jan 19, 2011 at 11:59:57PM +0100, matthieu castet wrote: > > > > > Le Wed, 19 Jan 2011 16:14:32 -0500, > > > > > Konrad Rzeszutek Wilk a écrit : > > > > > > > > > > > > > > > > I was just shown this[1] on Xen from an Ubuntu bug report[2]. > > > > > > > > > > > > > > > > [ 1.230382] NX-protecting the kernel data: 3884k > > > > > > > > [ 1.231002] BUG: unable to handle kernel paging request at > > > > > > > > c1782ae0 ... > > > > > > > > [ 1.231145] Call Trace: > > > > > > > > [ 1.231152] [] ? __change_page_attr+0x2c1/0x370 > > > > > > > > [ 1.231161] [] ? __purge_vmap_area_lazy+0xc1/0x180 > > > > > > > > [ 1.231169] [] ? > > > > > > > > __change_page_attr_set_clr+0x4c/0xb0 [ 1.231176] > > > > > > > > [] ? change_page_attr_set_clr+0x128/0x300 > > > > > > > > [ 1.231183] [] ? > > > > > > > > __raw_callee_save_xen_restore_fl+0x6/0x8 [ 1.231192] > > > > > > > > [] ? vprintk+0x171/0x3f0 [ 1.231198] [] ? > > > > > > > > set_memory_nx+0x5f/0x70 > > > > > > > > > > > > > > If you run it with Xen debugging enabled: > > > > > > > > > > > > > > [ 7.753329] NX-protecting the kernel data: 2400k > > > > > > > (XEN) mm.c:2389:d0 Bad type (saw 3c000003 != exp 70000000) for mfn > > > > > this happen if (x & (PGT_type_mask|PGT_pae_xen_l2)) != type) > > > > > > > > > > but > > > > > #define PGT_type_mask (7U<<29) /* Bits 29-31. */ > > > > > #define _PGT_pae_xen_l2 26 > > > > > #define PGT_pae_xen_l2 (1U<<_PGT_pae_xen_l2) > > > > > > > > > > but (exp type = 0x70000000) & (PGT_type_mask|PGT_pae_xen_l2) = > > > > > 0x60000000 > > > > > > > > > > So the exp type look strange. > > > > > #define _PGT_pinned 28 > > > > > #define PGT_pinned (1U<<_PGT_pinned) > > > > > > > > > > > > 1355a5 (pfn 15a5) (XEN) mm.c:889:d0 Error getting mfn 1355a5 (pfn > > > > > > > 15a5) from L1 entry 80000001355a5063 for l1e_owner=0, pg_owner=0 > > > > > > > (XEN) mm.c:4958:d0 ptwr_emulate: could not get_page_from_l1e() > > > > > > > [ 7.759087] BUG: unable to handle kernel paging request at > > > > > > > c82a4d28 [ 7.759087] IP: [] > > > > > > > xen_set_pte_atomic+0x21/0x2f [ 7.759087] *pdpt = > > > > > > > 0000000001663001 *pde = 00000000082db067 *pte = 80000000082a4061 .. > > > > > > > and same stack trace. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Does Xen have different size page table allocations or something > > > > > > > > weird? > > > > > > > > > > > > > > The same page size. Not sure actually why it is being triggered. > > > > > > > Let me copy Keir on this. Keir, the region that is being marked as > > > > > > > _NX is .bss one and > > > > > > > > > > > > > > > > _past_ the __init_end it dies. Any ideas? > > > > > > > > > > > Does this happen if you add ". = ALIGN(HPAGE_SIZE);" before bss section > > > > > in arch/x86/kernel/vmlinux.lds.S ? > > > > > > > > Like this? > > > Yes > > > > > > > > yeeeey...That made it boot. > > > > > > > > > > > > > > What's the output of kernel_page_tables debugfs ? > > > > > > > > Shees.. I get > > > > > > > > [ 73.723105] BUG: unable to handle kernel paging request at 15555000 > > > [...] > > > > with the patch and if I revert 5bd5a452662bc37c54fb6828db1a3faf87e6511c.. > > > > > > > > That looks to be another bug to hunt down. > > > > > > > No that the same bug : that the root cause. > > > > > > For some reason with xen, accessing some page tables (bss and after) make the > > > system crash. > > > > I think I know the failure in the first case - the swapper_pg_dir is marked as _RO > > and you are not suppose to make it _RW (unless you first do a bit of dance and switch > > over to another pagetable). The reason being that Xen has a symbiotic relationship > > with PV domains where pagetables are marked _RO so that any update to > > it will go through Xen so it can validate that we aren't doing anything stupid. > > > > But accessing the page table should be OK, not sure why it crashed - we > > aren't writting anything to it - just reading. > > > > Let me copy Ian on this - he might have better ideas. > > It's pretty hard to follow the quoted context above but it certainly > seems plausible that set_memory_nx could inadvertently end up trying to > make a page which Xen made RO into a RW again. > > For example the callchain appear to pass through static_protections() > which explicitly makes .data and .bss writeable, I think these regions > can potentially contain page table pages -- e.g. allocated from BRK > perhaps? They definitly do - it has the level1_ident_pgt, which is definitly used during bootup. Perhaps the fix is when marking NX, just do NX, don't try to set RW if they are RO. > > Ian. >