From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753648AbaHKOBK (ORCPT ); Mon, 11 Aug 2014 10:01:10 -0400 Received: from mail.skyhub.de ([78.46.96.112]:43962 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753370AbaHKOBI (ORCPT ); Mon, 11 Aug 2014 10:01:08 -0400 Date: Mon, 11 Aug 2014 16:00:57 +0200 From: Borislav Petkov To: Henrique de Moraes Holschuh Cc: H Peter Anvin , Fenghua Yu , linux-kernel@vger.kernel.org Subject: Re: BUG: early intel microcode update violating alignment rules Message-ID: <20140811140057.GA21693@pd.tnic> References: <20140809231911.GA4843@khazad-dum.debian.net> <20140811102245.GC4236@nazgul.tnic> <20140811131613.GA4541@khazad-dum.debian.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20140811131613.GA4541@khazad-dum.debian.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 11, 2014 at 10:16:13AM -0300, Henrique de Moraes Holschuh wrote: > On Mon, 11 Aug 2014, Borislav Petkov wrote: > > On Sat, Aug 09, 2014 at 08:19:11PM -0300, Henrique de Moraes Holschuh wrote: > > > Is there a way to fix this in the kernel for the BSP? > > > > I think you're looking at this the wrong way around. :-) The thing that > > needs fixing is the SDM since some CPUs seem to accept 16-byte unaligned > > microcode just fine. > > I often wonder how much of the Intel SDM is really a fairy tale... it > certainly has enough legends from times long past inside ;-) But just like > old stories, should you forget all about them, they sometimes grow fangs > back and get you when you're least prepared. > > Now, seriously, we're neither aligning the thing, nor checking any of it for > alignment, so userspace can mess with us at will. Unless it is trying to be > actively malicious, we'll get 4-byte alignment out of userspace for the data > inside the early initramfs (assuming the use of the common cpio tools: GNU > cpio and GNU pax), but that's it. > > I can easily propose fixes to reject incorrectly aligned data (and will do > so), but you *really* don't want to know the kind of crap I came up with to > try to align the microcode update for the BSP: Standard Lovecraftian Mythos > Safety Procedures apply! So I am turning to you for ideas... It seems to me you're looking for issues where there are none. We simply have to ask Intel people what's with the 16-byte alignment and fix the SDM, apparently. If the processor accepts the non-16-byte-aligned update, why do you care? -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. --