For those wondering what the exact attack vector is, the AMD advisory has some details:
> Improper validation in a model specific register (MSR) could allow a malicious program with ring0 access to modify SMM configuration while SMI lock is enabled, potentially leading to arbitrary code execution. [0]
> Improper validation in a model specific register (MSR) could allow a malicious program with ring0 access to modify SMM configuration while SMI lock is enabled, potentially leading to arbitrary code execution. [0]
[0]: https://www.amd.com/en/resources/product-security/bulletin/a...