Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753096AbaBQMfd (ORCPT ); Mon, 17 Feb 2014 07:35:33 -0500 Received: from fw-tnat.cambridge.arm.com ([217.140.96.21]:54491 "EHLO cam-smtp0.cambridge.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752939AbaBQMfb (ORCPT ); Mon, 17 Feb 2014 07:35:31 -0500 Date: Mon, 17 Feb 2014 12:34:21 +0000 From: Dave Martin To: Kees Cook Cc: Catalin Marinas , Will Deacon , Larry Bassel , Stephen Rothwell , Russell King , Nicolas Pitre , Ben Dooks , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Grant Likely , Jiang Liu , Christoffer Dall , Laura Abbott , Marc Zyngier , Rob Herring , Vitaly Andrianov , "linux-arm-kernel@lists.infradead.org" , Simon Baatz , Jonathan Austin , Greg Kroah-Hartman , LKML , Santosh Shilimkar , Andrew Morton Subject: Re: [PATCH 2/2] ARM: mm: keep rodata non-executable Message-ID: <20140217123415.GA2182@e103592.cambridge.arm.com> References: <1392339850-18686-1-git-send-email-keescook@chromium.org> <1392339850-18686-3-git-send-email-keescook@chromium.org> <20140214162257.GB2331@e103592.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 14, 2014 at 11:11:07AM -0800, Kees Cook wrote: > On Fri, Feb 14, 2014 at 8:22 AM, Dave Martin wrote: > > On Thu, Feb 13, 2014 at 05:04:10PM -0800, Kees Cook wrote: > >> Introduce "CONFIG_DEBUG_RODATA" to mostly match the x86 config, though > >> the behavior is different: it depends on STRICT_KERNMEM_PERMS, which > >> sets rodata read-only (but executable), where as this option additionally > >> splits rodata from the kernel text (resulting in potentially more memory > >> lost to padding) and sets it non-executable as well. The end result is > >> that on builds with CONFIG_DEBUG_RODATA=y (like x86) the rodata with be > >> marked purely read-only. > > > > This triggers an Oops in kexec, because we have a block of code in .text > > which is a template for generating baremetal code to relocate the new > > kernel, and some literal words are written into it before copying. > > You're writing into the text area? I would imagine that > CONFIG_ARM_KERNMEM_PERMS would break that. However, that's not the > right place to be building code -- shouldn't the module area be used > for that? > > > Possibly this should be in .rodata, not .text. > > Well, rodata should be neither writable nor executable. We're not writing into code exactly. This code is never executed in-place in vmlinux. It gets copied, and only copies are ever executed. Some pointers and offsets get poked into the code to configure it. I think it would be better simply to put the code in .rodata, and poke paramaters into the copy, not the original -- but that's a bit more awkward to code up, since the values can't be poked simply by writing global variables. > > > There may be a few other instances of this kind of thing. > > This config will certainly find them! :) But, that's why it's behind a config. I haven't tested exhaustively, but it think this is sufficient for a Tested-by. The patch does seem to be doing what it is intended to do, and doesn't seem to be triggering false positives all over the place. > > > Are you aware of similar situations on other arches? > > I think there were some problems a long time ago on x86 for rodata too. It would be good to get this kexec case fixed -- I'll try to hack up a separate patch. Cheers ---Dave -- 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/