Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752776AbbLHUjv (ORCPT ); Tue, 8 Dec 2015 15:39:51 -0500 Received: from terminus.zytor.com ([198.137.202.10]:60201 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752593AbbLHUjt (ORCPT ); Tue, 8 Dec 2015 15:39:49 -0500 User-Agent: K-9 Mail for Android In-Reply-To: References: <20151204164057.GE2514@codeblueprint.co.uk> <17EC94B0A072C34B8DCF0D30AD16044A0288EFC7@BPXM09GP.gisp.nec.co.jp> <20151208122557.GA2518@codeblueprint.co.uk> <20151208141946.GD27180@pd.tnic> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Subject: Re: [PATCH 1/2] x86: Fix kernel panic when booting with XD disabled in uEFI firmware From: "H. Peter Anvin" Date: Tue, 08 Dec 2015 12:39:14 -0800 To: Kees Cook , Borislav Petkov CC: Matt Fleming , Kosuke Tatsukawa , Thomas Gleixner , Ingo Molnar , "x86@kernel.org" , "linux-efi@vger.kernel.org" , "linux-kernel@vger.kernel.org" Message-ID: <19122B57-8052-4A92-801E-03CC84E66F06@zytor.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2253 Lines: 56 On December 8, 2015 12:30:06 PM PST, Kees Cook wrote: >On Tue, Dec 8, 2015 at 6:19 AM, Borislav Petkov wrote: >> On Tue, Dec 08, 2015 at 12:25:57PM +0000, Matt Fleming wrote: >>> On Mon, 07 Dec, at 11:10:43PM, Kosuke Tatsukawa wrote: >>> > >>> > Thank you pointing that out. >>> > >>> > linux-4.4-rc3 booted without a problem on a real server even with >XD >>> > turned off by the firmware. I didn't notice this before because I >was >> >> The aforementioned patch reenables NX. >> >>> Borislav, what do you think about stripping PAGE_NX from >'page_flags' >>> in kernel_map_pages_in_pgd() if NX isn't supported, rather than >>> returning EINVAL? At least that way EFI runtime services would still >>> work. >> >> I guess we can - I mean, I don't see what can go wrong more when >> allowing the kernel to execute even NX UEFI regions. Maybe easier >> generation of "gadgets" in the ROP sense ... >> >> On a related node, I'm very sceptical of the existence of this >"noexec" >> chicken bit, if you ask me. It is a really bad idea, security-wise, >to >> disable NX. Is there even a valid use case to disable NX? >> >> Because if not, I'd vote for removing that chicken bit or at least >> taining the kernel with >> >> add_taint(TAINT_USER_MORON, ... ); > >If we add this for not-nx, I would like to add it for not-rodata too. > >> Kees, has this NX disabling practice come up in the past, per >chance... ? > >I've never seen anyone actually use it. I was asked to include it out >of fear of some kind of rogue imagined CPU configuration that mixed NX >and non-NX capable CPUs in a single machine where the forced NX >re-enablement code would cause problems. As you might imagine, I'm not >aware of this case ever being an issue. ;) > >-Kees Actually I think of it much more as a debug option - being able to mimic NX-unaware hardware and to track down problems in the field. -- Sent from my Android device with K-9 Mail. Please excuse brevity and formatting. -- 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/