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22 Support shim fallback bootchain #106

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16 changes: 13 additions & 3 deletions gadget/gadget-amd64.yaml
Original file line number Diff line number Diff line change
Expand Up @@ -25,12 +25,22 @@ volumes:
type: C12A7328-F81F-11D2-BA4B-00A0C93EC93B
size: 1200M
update:
edition: 2
edition: 3
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content:
- source: shim.efi.signed
target: EFI/BOOT/BOOTX64.efi
- source: fbx64.efi
target: EFI/BOOT/fbx64.efi
- source: grubx64.efi
target: EFI/boot/grubx64.efi
target: EFI/BOOT/grubx64.efi

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Are we sure we need grub in EFI/BOOT? Afaiu reading shim code, shim would never run it if it finds EFI/BOOT/fbx64.efi

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I think you are right.

- source: mmx64.efi
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I think the mok manager should also go in EFI\ubuntu.

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Sounds good. I don't really know what the mok manager is used for, and there was some consternation about adding it in the past: #56 (comment)

It's not one of the boot assets added by the snapd PR #13205 (https://github.com/snapcore/snapd/pull/13205/files#diff-dca334c34d6acf0ce9fb49a95fb836caafe064f7fd2eda43a2185d6d9c7e20e5R464-R476), so I'm not sure if it's something we actually need to add.

What do you think?

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I would love to have it. The mok keys can be used to sign your own kernels. But it can also be used by anything that uses the secondary trusted keyring in the kernel: kernel modules, signed dm-verity, etc.

Also there is no security argument here, because there is a signed efi that anyone can install manually. We are just making it more annoying to install it for legitimate users.

If it causes some issues and would delay this PR, you do not have to add it.

But for sure, if we add it in EFI\BOOT, it should also go in EFI\ubuntu. It feels very weird to have it in only one. That would be, you can install machine owner keys, but only if in the bios, you force to boot the default efi bootloader (EFI\BOOT\bootx64.efi) instead of the configured BootOrder.

To sum up. Either add EFI\ubuntu\mmx64.efi or remove EFI\BOOT\mmx64.efi.

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Probably we can live with MokManager only in EFI\ubuntu, as we have seen that grub will not ever run from EFI\boot if we have fbx64.efi. As MM is called either when shim tries to run grub but it has not a valid signature or when the OS modifies EFI variables related to the MoK - and the OS is expected to have been started by grub in EFI\ubuntu.

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Sounds correct.

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Makes sense. I've removed it now, thanks!

target: EFI/BOOT/mmx64.efi
- source: BOOTX64.CSV
target: EFI/ubuntu/BOOTX64.CSV
- source: grubx64.efi
target: EFI/ubuntu/grubx64.efi
- source: shim.efi.signed
target: EFI/boot/bootx64.efi
target: EFI/ubuntu/shimx64.efi
- name: ubuntu-boot
role: system-boot
filesystem: ext4
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16 changes: 13 additions & 3 deletions gadget/gadget-arm64.yaml
Original file line number Diff line number Diff line change
Expand Up @@ -11,12 +11,22 @@ volumes:
type: C12A7328-F81F-11D2-BA4B-00A0C93EC93B
size: 1200M
update:
edition: 2
edition: 3
content:
- source: shim.efi.signed
target: EFI/BOOT/BOOTAA64.efi
- source: fbaa64.efi
target: EFI/BOOT/fbaa64.efi
- source: grubaa64.efi
target: EFI/boot/grubaa64.efi
target: EFI/BOOT/grubaa64.efi
- source: mmaa64.efi
target: EFI/BOOT/mmaa64.efi
- source: BOOTAA64.CSV
target: EFI/ubuntu/BOOTAA64.CSV
- source: grubaa64.efi
target: EFI/ubuntu/grubaa64.efi
- source: shim.efi.signed
target: EFI/boot/bootaa64.efi
target: EFI/ubuntu/shimaa64.efi
- name: ubuntu-boot
role: system-boot
filesystem: ext4
Expand Down