From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from cavan.codon.org.uk (cavan.codon.org.uk [176.126.240.207]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B2A6516A934; Mon, 19 Aug 2024 18:24:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=176.126.240.207 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724091874; cv=none; b=on3hHwl56sRTjSy81xgszfaw3gv3fpj9F1cz7BwvxPa+vXkMNdQND+q+vGK7pBi6a9A9Xu5UigUGN+k6LlsnqJIKluO7ICaTOAEbfGhuQ71CpIlJORmVZjixvucGJ4YyH6qYgo243WTTWaMLOpV09YHNECr4UAKKpQIAFkneAmk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724091874; c=relaxed/simple; bh=HHitbLQcODdjPuCSoJaZiVGwSe7pT6N18nHKmwnz0TQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=SwLpxV0LMlwt1fd3DqH14qPuf3m3AgCqKVETARIlpZGGZlvE7Kggs0ojX5xdSy2ifsn9bQgco6g1F+8/Dw/d6r/uIqNfVMev2qeRgNXwvMxlrRQZPHTNyqmfvkb5jnoPZMLOd5jUg1XMtxFTuxZL+7KKTK5VppY9oJjCyibI1Rg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=srcf.ucam.org; spf=pass smtp.mailfrom=codon.org.uk; arc=none smtp.client-ip=176.126.240.207 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=srcf.ucam.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=codon.org.uk Received: by cavan.codon.org.uk (Postfix, from userid 1000) id 2F2FF409FF; Mon, 19 Aug 2024 19:24:02 +0100 (BST) Date: Mon, 19 Aug 2024 19:24:02 +0100 From: Matthew Garrett To: Jarkko Sakkinen Cc: Andrew Cooper , Thomas Gleixner , "Daniel P. Smith" , "Eric W. Biederman" , 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, kexec@lists.infradead.org, linux-efi@vger.kernel.org, iommu@lists.linux-foundation.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, dave.hansen@linux.intel.com, ardb@kernel.org, James.Bottomley@hansenpartnership.com, peterhuewe@gmx.de, jgg@ziepe.ca, luto@amacapital.net, nivedita@alum.mit.edu, herbert@gondor.apana.org.au, davem@davemloft.net, corbet@lwn.net, dwmw2@infradead.org, baolu.lu@linux.intel.com, kanth.ghatraju@oracle.com, trenchboot-devel@googlegroups.com Subject: Re: [PATCH v9 06/19] x86: Add early SHA-1 support for Secure Launch early measurements Message-ID: References: <20240531010331.134441-1-ross.philipson@oracle.com> <20240531010331.134441-7-ross.philipson@oracle.com> <20240531021656.GA1502@sol.localdomain> <874jaegk8i.fsf@email.froward.int.ebiederm.org> <5b1ce8d3-516d-4dfd-a976-38e5cee1ef4e@apertussolutions.com> <87ttflli09.ffs@tglx> <550d15cd-5c48-4c20-92c2-f09a7e30adc9@citrix.com> Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Aug 19, 2024 at 09:05:47PM +0300, Jarkko Sakkinen wrote: > On Fri Aug 16, 2024 at 9:41 PM EEST, Matthew Garrett wrote: > > On Fri, Aug 16, 2024 at 02:22:04PM +0300, Jarkko Sakkinen wrote: > > > > > For (any) non-legacy features we can choose, which choices we choose to > > > support, and which we do not. This is not an oppositive view just saying > > > how it is, and platforms set of choices is not a selling argument. > > > > NIST still permits the use of SHA-1 until 2030, and the most significant > > demonstrated weaknesses in it don't seem applicable to the use case > > here. We certainly shouldn't encourage any new uses of it, and anyone > > who's able to use SHA-2 should be doing that instead, but it feels like > > people are arguing about not supporting hardware that exists in the real > > world for vibes reasons rather than it being a realistically attackable > > weakness (and if we really *are* that concerned about SHA-1, why are we > > still supporting TPM 1.2 at all?) > > We are life-supporting TPM 1.2 as long as necessary but neither the > support is extended nor new features will gain TPM 1.2 support. So > that is at least my policy for that feature. But the fact that we support it and provide no warning labels is a pretty clear indication that we're not actively trying to prevent people from using SHA-1 in the general case. Why is this a different case? Failing to support it actually opens an entire separate set of footgun opportunities in terms of the SHA-1 banks now being out of sync with the SHA-2 ones, so either way we're leaving people open to making poor choices.