Re: [PATCH v7 06/13] x86: Add early SHA support for Secure Launch early measurements

From: Andrew Cooper <andrew.cooper3@citrix.com>
To: James Bottomley <James.Bottomley@HansenPartnership.com>,
	Eric Biggers <ebiggers@kernel.org>,
	Ross Philipson <ross.philipson@oracle.com>
Cc: 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, ardb@kernel.org,
	mjg59@srcf.ucam.org, luto@amacapital.net, nivedita@alum.mit.edu,
	kanth.ghatraju@oracle.com, trenchboot-devel@googlegroups.com
Subject: Re: [PATCH v7 06/13] x86: Add early SHA support for Secure Launch early measurements
Date: Mon, 13 Nov 2023 23:21:36 +0000	[thread overview]
Message-ID: <8703f1a9-5d4d-4c5a-b9aa-3b31ad2dcd41@citrix.com> (raw)
In-Reply-To: <87f56530b85ea894036a74be1824d6f2716f70de.camel@HansenPartnership.com>

On 11/11/2023 8:36 pm, James Bottomley wrote:
> On Sat, 2023-11-11 at 18:19 +0000, Andrew Cooper wrote:
>> On 11/11/2023 5:44 pm, Eric Biggers wrote:
>>> On Fri, Nov 10, 2023 at 05:27:44PM -0500, Ross Philipson wrote:
>>>>  arch/x86/boot/compressed/early_sha1.c   | 12 ++++
>>>>  lib/crypto/sha1.c                       | 81
>>>> +++++++++++++++++++++++++
>>> It's surprising to still see this new use of SHA-1 after so many
>>> people objected to it in the v6 patchset.  It's also frustrating
>>> that the SHA-1 support is still being obfuscated by being combined
>>> in one patch with SHA-2 support, perhaps in an attempt to conflate
>>> the two algorithms and avoid having to give a rationale for the
>>> inclusion of SHA-1.  Finally, new functions should not be added to
>>> lib/crypto/sha1.c unless those functions have multiple users.
>> The rational was given.  Let me reiterate it.
>>
>> There are real TPMs in the world that can't use SHA-2.  The use of
>> SHA-1 is necessary to support DRTM on such systems, and there are
>> real users of such configurations.
> Given that TPM 2.0 has been shipping in bulk since Windows 10 (2015)
> and is required for Windows 11 (2021), are there really such huge
> numbers of TPM 1.2 systems involved in security functions?

Yes.

As ever, it's not as simple as a straight TPM version issue.

AMD's firmware-TPM2 isn't compatible with their DRTM implementation. 
Users are limited to whatever headers are available on the motherboard.

Furthermore, even with a TPM2, it is the firmware (Intel TXT ACM) or
hardware (AMD SKINIT) which chooses the hash algorithms to use, and in a
lot of cases the end user doesn't get a choice.

So yes - there really are modern systems which you can't use SHA-2-only
with.

>> DRTM with SHA-1-only is a damnsight better than no DTRM, even if SHA-
>> 1 is getting a little long in the tooth.
> That's not the problem.  The problem is that sha1 is seen as a
> compromised algorithm by NIST which began deprecating it in 2011 and is
> now requiring it to be removed from all systems supplied to the US
> government by 2030

This is a non-issue.

People who care about having no SHA-1 can not compile in DRTM support.

But there are people who will tolerate SHA-1 code to get DTRM support.

~Andrew

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