CP-312160: secureboot certificate update design doc

[chunjiez]

Microsoft Secure Boot certificates from 2011 are reaching end-of-life, and legacy VMs may still contain only the old certificate set.

We design an out-of-band mechanism to update per-VM UEFI Secure Boot variables safely and at scale.

[dinhngtu]

Thanks for the document.

I'd like to ask a couple questions:

• There's no detection or handling of VMs with Secure Boot PCR7 binding. Is this explicitly out of scope and up to the admins to decide?
• The certificate update check helper is not yet detailed. As EFI variable handling is part of varstored, is it a script that's part of varstored, or something else? Does it actively connect to XAPI and read the VM state or does it simply check the EFI-variables data handed over by XAPI (i.e. is it an active or passive script)?
• (technically a question for varstored) Does the update involve a full override of all Secure Boot variables, or does it only overwrite/append a few specific ones?

[robhoes]

Thanks @chunjiez, this toolstack design accurately reflects what we have discussed internally.

From @dinhngtu's question, I think it would be good to add some more details about the interfaces between varstored and xapi:

• A script will be introduced, which xapi calls to determine the SB cert state. Please explain the inputs, that it comes uses a library shared with varstored and that it will be deprivileged like varstored.
• varstored uses the existing varstored-guard process to make calls to xapi, which will need to be extended.

[lindig]

The names and the meaning seem to diverge. If an update is required, the state should reflect that and not dance around it.

• ok
• update_required
• reboot_required

In the current proposal it is not obvious what is expected from the user.

[lindig]

"including" could mean that there are more but unlisted objects. Would say: "these VM-class objects:"

[lindig]

Would marked or scheduled be better?

[lindig]

I find the name ambiguous. Does it mean: this is an update? This has been updated? Is update a state (noun) or an action (verb)?

[stephenchengCloud]

It means it will be updated after calling set_NVRAM_EFI_variables

But shoult it be:
update=yes -> set state ok

[psafont]

I think a simple state diagram done in mermaid would work well to show the interactions between this field and the NVRAM

https://mermaid.ai/open-source/syntax/stateDiagram.html

[psafont]

Can this flow end up in an invalid state that needs to be recovered from? That is, neither the new nor the outdated certificates are stored in the NVRAM