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

[Jarkko Sakkinen]

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@xxxxxxxxxxxxxxxxxxxx>
> > 
> > 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@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Ross Philipson <ross.philipson@xxxxxxxxxx>
>
> 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