Is this (relatively) new?
I don't use TPM and I rarely update BIOS unless I really need to, but I thought there was an option on my BIOS/UEFI to use USB drive to update it. How would Windows know about it?
The BIOS update instructions for my retail packaged motherboard indicate to turn off BitLocker before doing upgrades to prevent loss of TPM turning into a loss of access, but it'd be easier if it were automated.
Slightly off-topic: it also cheats in how TPM works for Bitlocker when you do TPM + PIN. One would assume PIN becomes part of the encryption key, but in reality, it's just used as the auth for TPM to release the key. So while it sounds like a two-factor solution, in reality it's just single factor.
So the Bitlocker without TPM is actually a better idea and Windows makes it very painful to do if TPM is on.
I’m not sure how the typical “two factor” best practices would interpret one of the factors basically self destructing after 10 guesses, but IMO it’s a pretty decent system if done right.
If you're wondering, yes this is a security issue in practice. There have been TPM vulnerabilities in the past that enabled exfiltration of secrets.
Actually, this is not the case. BitLocker wraps the key, meaning even if the TPM were compromised, one would still have to brute-force the PIN for the actual key. It’s cryptsetup on Linux that stores the key on the TPM in plaintext. This vulnerability has been known for quite a while and nothing has been done about it so far.
https://arxiv.org/abs/2304.14717
Apart from Windows, there are many setups that fail in fun ways: Kubernetes pods that migrate from one VM with a TPM to another one, hypervisors that mount a virtual TPM to VMs, containers or VM images that do Tailscale registration on one machine and then get replicated to others, etc.
Tailscale already did some attempts at cleverness when deciding whether to enable features using a TPM (e.g. probing for TPM health/version on startup, disabling node state encryption on Kubernetes pods), but there was still a long tail of edge cases.