[PATCH RFC 0/4] efi: CapsuleUpdate: support for dynamic GUIDs

[Ilias Apalodimas]

Hi Caleb

On Fri, 26 Apr 2024 at 17:19, Caleb Connolly <caleb.connolly at linaro.org> wrote:
>
> As more boards adopt support for the EFI CapsuleUpdate mechanism, there
> is a growing issue of being able to target updates to them properly. The
> current mechanism of hardcoding UUIDs for each board at compile time is
> unsustainable, and maintaining lists of GUIDs is similarly cumbersome.
>
> In this series, I propose that we adopt v5 GUIDs, these are generated
> by using a well-known salt GUID as well as board specific information
> (like the model/revision), these are hashed together and the result is
> truncated to form a new UUID.
>
> The well-known salt GUID can be specific to the architecture (SoC
> vendor), or OEM. Exact rules on how these are used (e.g. if vendors
> should be told to generate their own for their products, and if that
> can be added upstream, etc) will need to be decided.
>
> Specifically, the following fields are used to generate a GUID for a
> particular fw_image:
>
> * namespace salt
> * soc name
> * board model (usually from dt root model property)
> * board compatible (usually the first entry in the dt root compatible
>   array).
> * fw_image name (the string identifying the specific image, especially
>   relevant for board that can update multiple images).
>
> Once generated, the GUIDs can be printed with the "%pUs" format string,
> these can then be stored externally to U-Boot.
>
> The SoC name field might be controversial, it could be generated from
> the last entry in the dt root compatible in most cases, or in some board
> specific way. It might make sense to remove this field if it is
> unfeasible for some boards.
>
> == Usage ==
>
> Boards can integrate dynamic UUID support as follows:
>
> 1. Adjust Kconfig to depend on EFI_CAPSULE_DYNAMIC_UUIDS if
>    EFI_HAVE_CAPSULE_SUPPORT
> 2. Skip setting the fw_images image_type_id property.
> 3. In board_init() (or anywhere before the EFI subsystem is
>    initialised), add a call to efi_capsule_update_info_gen_ids() with
>    the board specific info.
>
> == Limitations ==
>
> * Changing GUIDs
>
> The primary limitation with this approach is that if any of the source
> fields change, so will the GUID for the board. It is therefore pretty
> important to ensure that GUID changes are caught during development.
>
> * Supporting multiple boards with a single image
>
> This now requires having an entry with the GUID for every board which
> might lead to larger UpdateCapsule images.
>
> == Tooling ==
>
> Not part of this RFC is a tool to generate the GUIDs outside of U-Boot.
> I suspect this might be a requirement, but it makes sense to decide on
> what fields we use first.

Yes, tooling would be good.

>
> The tool should take in the salt, DTB, and a list of fw_image names. It
> could also accept values to overwrite the individual fields if they
> aren't derived from the DTB for some reason. It would then generate the
> expected GUID.
>
> A potential idea here would be to integrate this into the build system
> so that it prints a warning if the GUID changes.
>

There's work being done in that direction as far as capsules are
concerned. Apart from the u-boot binary from your board, the build
system should also generate binaries

Thanks
/Ilias

> == TOOD ==
>
> Missing from this RFC are unit tests for the dynamic UUID feature, these
> will be implemented for future revisions.
>
> I would appreciate any feedback on the above.
>
> This follows a related discussion started by Ilias:
> https://lore.kernel.org/u-boot/CAC_iWjJNHa4gMF897MqYZNdbgjFG8K4kwGsTXWuy72WkYLizrw@mail.gmail.com/
>
> ---
> Caleb Connolly (4):
>       lib: uuid: add UUID v5 support
>       efi: add a helper to generate dynamic UUIDs
>       doc: uefi: document dynamic GUID generation
>       sandbox: switch to dynamic UUIDs
>
>  arch/Kconfig                 |  1 +
>  board/sandbox/sandbox.c      | 28 +++++++++++++++-------------
>  doc/develop/uefi/uefi.rst    | 35 +++++++++++++++++++++++++++++++++++
>  include/efi_loader.h         | 28 ++++++++++++++++++++++++++++
>  include/uuid.h               | 16 ++++++++++++++++
>  lib/Kconfig                  |  8 ++++++++
>  lib/efi_loader/Kconfig       | 14 ++++++++++++++
>  lib/efi_loader/efi_capsule.c | 33 +++++++++++++++++++++++++++++++++
>  lib/uuid.c                   | 33 +++++++++++++++++++++++++++++++++
>  9 files changed, 183 insertions(+), 13 deletions(-)
> ---
> change-id: 20240422-b4-dynamic-uuid-1a5ab1486c27
> base-commit: d097f9e1299a3bdb7de468f0d9bbc63932f461cd
>
> // Caleb (they/them)
>