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

[Matthew Garrett]

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.