Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755514AbaBUMiS (ORCPT ); Fri, 21 Feb 2014 07:38:18 -0500 Received: from fw-tnat.cambridge.arm.com ([217.140.96.21]:54668 "EHLO cam-smtp0.cambridge.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754569AbaBUMiQ (ORCPT ); Fri, 21 Feb 2014 07:38:16 -0500 Date: Fri, 21 Feb 2014 12:37:04 +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" , Jonathan Austin , Simon Baatz , Greg Kroah-Hartman , LKML , Santosh Shilimkar , Andrew Morton Subject: Re: [PATCH 2/2] ARM: mm: keep rodata non-executable Message-ID: <20140221123645.GA2578@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> <20140217123415.GA2182@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 Tue, Feb 18, 2014 at 10:10:03AM -0800, Kees Cook wrote: > On Mon, Feb 17, 2014 at 4:34 AM, Dave Martin wrote: > > 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. > > Okay, interesting. I'll be curious to see what the patch for this looks like. > > >> > 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. > > Great, thanks for taking the time to check on it! > > Should I send this to the patch tracker, or wait for more feedback? It would be good if someone who's more familiar with the parms and vmlinux.lds stuff could take a look at it, though I don't see any obvious problem yet. If you don't receive further comments, you could try reposting once to alert people to the fact that you're still waiting. 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/