From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D06E9C7EE24 for ; Fri, 12 May 2023 11:28:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240395AbjELL24 (ORCPT ); Fri, 12 May 2023 07:28:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52208 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240333AbjELL2z (ORCPT ); Fri, 12 May 2023 07:28:55 -0400 Received: from cavan.codon.org.uk (irc.codon.org.uk [IPv6:2a00:1098:84:22e::2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA691D2E0; Fri, 12 May 2023 04:28:48 -0700 (PDT) Received: by cavan.codon.org.uk (Postfix, from userid 1000) id 68D0D40A6F; Fri, 12 May 2023 12:28:47 +0100 (BST) Date: Fri, 12 May 2023 12:28:47 +0100 From: Matthew Garrett To: Ard Biesheuvel Cc: Eric Biggers , Ross Philipson , linux-kernel@vger.kernel.org, x86@kernel.org, linux-integrity@vger.kernel.org, linux-doc@vger.kernel.org, linux-crypto@vger.kernel.org, iommu@lists.linux-foundation.org, kexec@lists.infradead.org, linux-efi@vger.kernel.org, dpsmith@apertussolutions.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, James.Bottomley@hansenpartnership.com, luto@amacapital.net, nivedita@alum.mit.edu, kanth.ghatraju@oracle.com, trenchboot-devel@googlegroups.com Subject: Re: [PATCH v6 06/14] x86: Add early SHA support for Secure Launch early measurements Message-ID: <20230512112847.GF14461@srcf.ucam.org> References: <20230504145023.835096-1-ross.philipson@oracle.com> <20230504145023.835096-7-ross.philipson@oracle.com> <20230510012144.GA1851@quark.localdomain> <20230512110455.GD14461@srcf.ucam.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org On Fri, May 12, 2023 at 01:18:45PM +0200, Ard Biesheuvel wrote: > On Fri, 12 May 2023 at 13:04, Matthew Garrett wrote: > > > > On Tue, May 09, 2023 at 06:21:44PM -0700, Eric Biggers wrote: > > > > > SHA-1 is insecure. Why are you still using SHA-1? Don't TPMs support SHA-2 > > > now? > > > > TXT is supported on some TPM 1.2 systems as well. TPM 2 systems are also > > at the whim of the firmware in terms of whether the SHA-2 banks are > > enabled. But even if the SHA-2 banks are enabled, if you suddenly stop > > extending the SHA-1 banks, a malicious actor can later turn up and > > extend whatever they want into them and present a SHA-1-only > > attestation. Ideally whatever is handling that attestation should know > > whether or not to expect an attestation with SHA-2, but the easiest way > > to maintain security is to always extend all banks. > > > > Wouldn't it make more sense to measure some terminating event into the > SHA-1 banks instead? Unless we assert that SHA-1 events are unsupported, it seems a bit odd to force a policy on people who have both banks enabled. People with mixed fleets are potentially going to be dealing with SHA-1 measurements for a while yet, and while there's obviously a security benefit in using SHA-2 instead it'd be irritating to have to maintain two attestation policies.