secureboot: add check to validate signature db certificates before updating

[Rolv-Apneseth]

Closes #1099

The main concern this resolves is that, with the Microsoft UEFI CA 2011 Certificate having expired, any further updates to the shim will not be dual-signed, and will only be signed by the 2023 key. This means that any system with Secure Boot enabled will be broken if bootupd updates the shim and the system does not have the certificate available in their firmware's signature database. So we should make sure bootupd is aware of this requirement so we don't break user's Secure Boot systems.

As stated in the issue, we wanted a way to incorporate some of the sbchooser logic to achieve this goal. However, I found this crate which suits our use-case perfectly. I discussed briefly with the creator and he agreed it was a good fit.

I've implemented this in such a way that any update will be blocked if Secure Boot is enabled and the 2023 cert is not in the system's signature DB. So updating is allowed as long as any one of the following is true:

1. System is not EFI-booted
2. System does not have Secure Boot enabled
3. System has the 2023 cert in the signature database

Something that might be nice but would add some complexity is only blocking updates if the shim is actually being updated, as that's the only one that matters here. Any thoughts on this? I think it's gonna be a brief enough window where this is actually helpful that keeping it as simple as possible will benefit us more in the long run. Plus Secure Boot systems with outdated certificates should indeed have their firmware updated as soon as possible. I'd be happy to try implement the module comparison logic if we think it's important to only block on shim updates though.

Also for testing, I have a positive case test, and tested the negative case manually. I can't think of a good way to test the negative case with kola. Maybe including a feature in kola to enable using the db with an older certificate (binary blob?), but I'm not sure that's worth it.

Summary by CodeRabbit

• New Features

  • Added Secure Boot compatibility validation for EFI-based systems.
  • Updates now verify that the Microsoft UEFI CA 2023 certificate is present when Secure Boot is enabled.
  • Updates proceed when Secure Boot is disabled or the required certificate is available.

• Bug Fixes

  • Prevents updates when required Secure Boot certificate validation fails or EFI security data cannot be read.

• Tests

  • Added coverage for Secure Boot validation during EFI updates.

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• src/secureboot.rs

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📝 Walkthrough

Walkthrough

The change adds EFI-only Secure Boot certificate validation. Update preparation checks for the Microsoft UEFI CA 2023 certificate before continuing. A new qemu kola test exercises the validation on an x86_64 Secure Boot system.

Changes

Secure Boot certificate validation

Layer / File(s)	Summary
EFI certificate validation Cargo.toml, src/main.rs, src/secureboot.rs	Adds the EFI dependency and gated module. The validator reads Secure Boot state and the db signature database, then checks for the Microsoft UEFI CA 2023 certificate.
Update preparation integration src/bootupd.rs, tests/kola/test-secureboot	Runs validation before EFI update preparation continues. Adds a qemu kola test for an x86_64 Secure Boot system.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to fd644

The change adds Secure Boot certificate validation before updates; no actionable merge-blocking risk remains beyond normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant bootupctl
  participant bootupd
  participant secureboot
  participant EFI_variables
  bootupctl->>bootupd: request update
  bootupd->>secureboot: validate_secureboot_for_update()
  secureboot->>EFI_variables: read SecureBoot and db
  EFI_variables-->>secureboot: Secure Boot state and signatures
  secureboot-->>bootupd: continue or return validation error
  bootupd-->>bootupctl: update result

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: adding a Secure Boot signature database certificate check before updates.
Linked Issues check	✅ Passed	The changes satisfy issue #1099 by checking EFI systems with Secure Boot enabled for the Microsoft UEFI CA 2023 certificate and blocking updates when the certificate is missing or cannot be read. Non-…
Out of Scope Changes check	✅ Passed	All changes support the linked issue. The dependency, validation module, update hook, and positive kola test are within scope.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 3 files.

Full details: Linked Issues check

Explanation

The changes satisfy issue #1099 by checking EFI systems with Secure Boot enabled for the Microsoft UEFI CA 2023 certificate and blocking updates when the certificate is missing or cannot be read. Non-EFI systems and systems with Secure Boot disabled remain unaffected.

✨ Finishing Touches

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• Create PR with unit tests

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Actionable comments posted: 1

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Inline comments:
In `@src/secureboot.rs`:
- Around line 20-28: Update is_secureboot_enabled to return an error when
sysfs::varstore_read cannot read SECURE_BOOT or var.data() is empty, and return
success with disabled status only when the readable first byte is zero. Update
validate_secureboot_for_update to propagate these errors while skipping the
signature database check only for a confirmed zero value, and add regression
coverage for both unknown-state failures and the readable-disabled path.

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📒 Files selected for processing (5)

• Cargo.toml
• src/bootupd.rs
• src/main.rs
• src/secureboot.rs
• tests/kola/test-secureboot

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