From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751034Ab1AVFVl (ORCPT ); Sat, 22 Jan 2011 00:21:41 -0500 Received: from smtp02.lnh.mail.rcn.net ([207.172.157.102]:10526 "EHLO smtp02.lnh.mail.rcn.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750875Ab1AVFVk (ORCPT ); Sat, 22 Jan 2011 00:21:40 -0500 X-Greylist: delayed 574 seconds by postgrey-1.27 at vger.kernel.org; Sat, 22 Jan 2011 00:21:40 EST Date: Sat, 22 Jan 2011 00:11:34 -0500 From: Konrad Rzeszutek Wilk To: matthieu castet Cc: Ian Campbell , 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 , konrad@kernel.org Subject: Re: [tip:x86/security] x86: Add NX protection for kernel data Message-ID: <20110122051134.GA6905@dumpdata.com> References: <20110119233824.GA2869@dumpdata.com> <1295522306.4d381a02b1e10@imp.free.fr> <20110120150618.GC5092@dumpdata.com> <1295537856.14780.54.camel@zakaz.uk.xensource.com> <20110120190531.GA9687@dumpdata.com> <4D3899AB.60207@free.fr> <20110120210436.GA1810@dumpdata.com> <20110120211939.GA32262@dumpdata.com> <20110120215556.GA29700@dumpdata.com> <4D39FDA2.2000305@free.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4D39FDA2.2000305@free.fr> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 21, 2011 at 10:41:54PM +0100, matthieu castet wrote: > Konrad Rzeszutek Wilk a écrit : >>> - * .data and .bss should always be writable. >>> + * .data and .bss should always be writable, but xen won't like >>> + * if we make page table rw (that live in .data or .bss) >>> */ >>> +#ifdef CONFIG_X86_32 >>> if (within(address, (unsigned long)_sdata, (unsigned long)_edata) || >>> - within(address, (unsigned long)__bss_start, (unsigned long)__bss_stop)) >>> - pgprot_val(required) |= _PAGE_RW; >>> + within(address, (unsigned long)__bss_start, (unsigned long)__bss_stop)) { >>> + unsigned int level; >>> + if (lookup_address(address, &level) && (level != PG_LEVEL_4K)) >>> + pgprot_val(forbidden) |= _PAGE_RW; >>> + } >>> +#endif >>> #if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA) >>> >>> fyi, it does make it boot. >> >> Hold it.. ccache is a wonderful tool but I think I've just "rebuilt" the >> binaries with the .bss HPAGE_ALIGN aligment by mistake, so this path got never >> taken. >> >> > Ok, > > ATM I saw the following solution to solve the problem : > 1) remove the data/bss check in static_protections, it was introduced by NX patches (64edc8ed). But I am not sure it > is really needed anymore. > 2) add ". = ALIGN(HPAGE_SIZE)" somewhere after init section. But if we want not to be allocated in image we > should put it before bss. And if we want to be freed after init, we should put before .init.end. > This mean moving .smp_locks (and .data_nosave when x86 will be added) before init section. I have no idea of the impact. > 3) add some logic in arch/x86/xen/mmu.c, that will ignore RW page setting for the page table marked RO. > 4) make static_protections take and old_prot argument, and only apply RW .data/.bss requirement if page is already RW. > > If possible I will go for 1). Sounds good. Just send me the patch and I will test it.