Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754632Ab3GAPzG (ORCPT ); Mon, 1 Jul 2013 11:55:06 -0400 Received: from mail-ie0-f175.google.com ([209.85.223.175]:58688 "EHLO mail-ie0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753291Ab3GAPzE (ORCPT ); Mon, 1 Jul 2013 11:55:04 -0400 MIME-Version: 1.0 In-Reply-To: <51D18B16.1000402@linux.intel.com> References: <20130630040514.GA20587@www.outflux.net> <51D18B16.1000402@linux.intel.com> Date: Mon, 1 Jul 2013 08:55:03 -0700 X-Google-Sender-Auth: Ql0yUGaRtitGh0w8SaC856gA4H4 Message-ID: Subject: Re: [PATCH] x86, kernel: make dump_pagetables a tristate From: Kees Cook To: Arjan van de Ven Cc: LKML , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "x86@kernel.org" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1913 Lines: 49 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). -Kees -- Kees Cook Chrome OS Security -- 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/