[Bug 1939565] Re: kernel signed by mok failed to boot if secure boot is on

[Jacob]

Hi Steve Langasek,
If an attacker is able to sign a custom kernel module & compromise a system via that means is there a reason to restrict the rather easy to use `update-secureboot-policy --new-key` method to only kernel modules? (Can we modify it to allow signing kernels in addition to kernel modules?)

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Title:
  kernel signed by mok failed to boot if secure boot is on

Status in OEM Priority Project:
  Confirmed
Status in shim package in Ubuntu:
  Incomplete

Bug description:
  On Focal, create a mok and enroll it, use it to sign test kernel as
  the secure boot is on.

  # sh -x test.sh 
  + sbverify --cert TestKer.pem /boot/vmlinuz-5.13.0-9010-oem
  Signature verification OK
  + openssl x509 -in TestKer.pem -outform der -out TestKernel.der
  + mokutil --test-key TestKernel.der
  TestKernel.der is already enrolled

  As the secure boot is on, can't load above kernel.

  The error message is:

  /boot/vmlinuz-5.13.0-9010-oem has invalid signature.

  Machine: Latitude 7520
  bios: 1.6.0
  shim-signed: 1.40.6+15.4-0ubuntu7
  grub-efi-amd64-signed: 1.167.2+2.04-1ubuntu44.2

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