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 421FBC77B75 for ; Fri, 12 May 2023 13:24:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241222AbjELNYJ (ORCPT ); Fri, 12 May 2023 09:24:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45506 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240965AbjELNYH (ORCPT ); Fri, 12 May 2023 09:24:07 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A8F231715; Fri, 12 May 2023 06:24:06 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1683897845; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=EGpiykIbZrzhClWEawyzh/+46DdyV3m0l/aogql4GLM=; b=t4zuosmBFyYyCvcFt4CogxekyLnafjtx8UdgZrID9B7MkOZFFbFZUGHMqQ4w/49f+dprnT PlH4xsuf9SnZUOj7+doXTmxlro1g3dwnvALxgbiT8zqrKR4AJUen8DhiEMHG4VUhgD4slv C9X56nGsqINm+67cMkF7EU6EiQxHU/23YN7VvK9EXvyfvLTW68S7L4dUwXmA35Ei9TL036 gu+4asg1Taks0CJq2S+2OB9lkYShGaLJrhnbaqnWk9mEnRuWFWa0Oz6nGQs8cOSPyCJwEi c2jvlBPs3mnLU2prsZbpx8tLhNGXy5wbGzwLrxlQo7WZLAontnM3cRvFOEMokA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1683897845; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=EGpiykIbZrzhClWEawyzh/+46DdyV3m0l/aogql4GLM=; b=R8wbDPOZoeZXva36wF885TESy/aZyCr3jMp5vxQyYINiluGTuOY4gRqy+MdP5jxH24QHtN tWf4/obwdQJm8xBQ== To: Matthew Garrett , 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, 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 In-Reply-To: <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> <20230512112847.GF14461@srcf.ucam.org> Date: Fri, 12 May 2023 15:24:04 +0200 Message-ID: <87pm75bs3v.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org On Fri, May 12 2023 at 12:28, Matthew Garrett wrote: > 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. Why? If you have a mixed fleet then it's not too much asked to provide two data sets. On a TPM2 system you can enforce SHA-2 and only fallback to SHA-1 on TPM 1.2 hardware. No? Thanks, tglx