Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754083Ab3GAQfW (ORCPT ); Mon, 1 Jul 2013 12:35:22 -0400 Received: from mga14.intel.com ([143.182.124.37]:27863 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752688Ab3GAQfV (ORCPT ); Mon, 1 Jul 2013 12:35:21 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,975,1363158000"; d="scan'208";a="262694704" Message-ID: <51D1AFC8.80803@linux.intel.com> Date: Mon, 01 Jul 2013 09:35:20 -0700 From: Arjan van de Ven User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130620 Thunderbird/17.0.7 MIME-Version: 1.0 To: Kees Cook CC: LKML , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "x86@kernel.org" Subject: Re: [PATCH] x86, kernel: make dump_pagetables a tristate References: <20130630040514.GA20587@www.outflux.net> <51D18B16.1000402@linux.intel.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2092 Lines: 50 On 7/1/2013 8:55 AM, Kees Cook wrote: > On Mon, Jul 1, 2013 at 6:58 AM, Arjan van de Ven wrote: >> On 6/29/2013 9:05 PM, Kees Cook wrote: >>> >>> Being able to examine page tables is handy, so make this a module that >>> can be loaded as needed. >> >> I personally don't think this is a good idea due to the various >> security/etc implications of this feature... should really just >> be off for non-debug kernels, not "off unless you load the module" > > I struggled with this too, but I couldn't come up with any reason that > made sense. If a system is running without modules_disabled, this code > is still loadable: > https://www.outflux.net/blog/archives/2011/04/27/non-executable-kernel-memory-progress/ > > The root user just needs to look at /proc/kallsyms before passing an > argument. So having it NOT a tristate doesn't actually change anything > except make it awkward to get it done. > > If a system is running with verified modules, then just not > signing/including ptdump makes it unavailable. And running with > modules_disabled, obviously, blocks it. > >>> +#ifdef CONFIG_X86_64 >>> +EXPORT_SYMBOL_GPL(init_level4_pgt); >>> +#else >>> +EXPORT_SYMBOL_GPL(swapper_pg_dir); >>> +#endif >> >> like these really have no business in any module > > Well, that's why I took me 2 years to send this patch. Those symbols > shouldn't be used outside of page table debugging, so it didn't really > seem upstreamable. However, now that I need to do regular examination > of the page tables, I wanted to do it without the hacky thing above. I > want to do at will on our test images (we use the same kernel for > production and test, but production images leave out the test modules, > etc). the code is small... how about making it a command line option to enable? rather than making something like this a module -- 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/