linux-kernel - Re: [PATCH v6 06/14] x86: Add early SHA support for Secure Launch early measurements

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Message-Id: <CSIYAN7SXASE.34Z0FBRCENLAI@suppilovahvero>
Date:   Thu, 11 May 2023 01:28:33 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "Eric Biggers" <ebiggers@...nel.org>,
        "Ross Philipson" <ross.philipson@...cle.com>
Cc:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        <linux-integrity@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-crypto@...r.kernel.org>, <iommu@...ts.linux-foundation.org>,
        <kexec@...ts.infradead.org>, <linux-efi@...r.kernel.org>,
        <dpsmith@...rtussolutions.com>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <bp@...en8.de>, <hpa@...or.com>,
        <ardb@...nel.org>, <mjg59@...f.ucam.org>,
        <James.Bottomley@...senpartnership.com>, <luto@...capital.net>,
        <nivedita@...m.mit.edu>, <kanth.ghatraju@...cle.com>,
        <trenchboot-devel@...glegroups.com>
Subject: Re: [PATCH v6 06/14] x86: Add early SHA support for Secure Launch
 early measurements

On Wed May 10, 2023 at 4:21 AM EEST, Eric Biggers wrote:
> On Thu, May 04, 2023 at 02:50:15PM +0000, Ross Philipson wrote:
> > From: "Daniel P. Smith" <dpsmith@...rtussolutions.com>
> > 
> > The SHA algorithms are necessary to measure configuration information into
> > the TPM as early as possible before using the values. This implementation
> > uses the established approach of #including the SHA libraries directly in
> > the code since the compressed kernel is not uncompressed at this point.
> > 
> > The SHA code here has its origins in the code from the main kernel:
> > 
> > commit c4d5b9ffa31f ("crypto: sha1 - implement base layer for SHA-1")
> > 
> > That code could not be pulled directly into the setup portion of the
> > compressed kernel because of other dependencies it pulls in. The result
> > is this is a modified copy of that code that still leverages the core
> > SHA algorithms.
> > 
> > Signed-off-by: Daniel P. Smith <dpsmith@...rtussolutions.com>
> > Signed-off-by: Ross Philipson <ross.philipson@...cle.com>
>
> SHA-1 is insecure.  Why are you still using SHA-1?  Don't TPMs support SHA-2
> now?
>
> And if you absolutely MUST use SHA-1 despite it being insecure, please at least
> don't obfuscate it by calling it simply "SHA".

AFAIK the TCG specs require for any TPM2 implementation to support both
SHA-1 and SHA-256, so this as a new feature should lock in to the
latter.

BR, Jarkko