FwupdPlugin – 1.0: Plugin: UEFI Capsule
Description: Reference for FwupdPlugin-1.0: Plugin: UEFI Capsule

#### Plugin: UEFI Capsule

## Introduction

The Unified Extensible Firmware Interface (UEFI) is a specification that defines the software interface between an OS and platform firmware. With the UpdateCapsule boot service it can be used to update system firmware.

If you don’t want or need this functionality you can use the `-Dplugin_uefi_capsule=disabled` option.

When this plugin is enabled, the companion UEFI binary may also be built from the fwupd-efi project if not already present on the filesystem. This behavior can be overridden using the meson option `-Defi_binary=false`.

For this companion binary to work with secure boot, it will need to be signed by an authority trusted with shim and/or the host environment.

## Lenovo Specific Behavior

On Lenovo hardware only the boot label is set to `Linux-Firmware-Updater` rather than “Linux Firmware Updater” (with spaces) due to long-fixed EFI boot manager bugs. Many users will have these old BIOS versions installed and so we use the `use-legacy-bootmgr-desc` quirk to use the safe name.

On some Lenovo hardware only one capsule is installable due to possible problems with the UpdateCapsule coalesce operation. As soon as one UEFI device has been scheduled for update the other UEFI devices found in the ESRT will be marked as `updatable-hidden` rather than `updatable`. Rebooting will restore them so they can be updated on next OS boot.

## Firmware Format

The daemon will decompress the cabinet archive and extract a firmware blob in EFI capsule file format.

See the UEFI specification for details.

This plugin supports the following protocol ID:

- `org.uefi.capsule`

## Version Format

The ESRT table is the way the firmware tells fwupd about what devices are updatable. Unfortunately the information it contains is minimal:

- GUID of the sub-component
- Enumerated result of the last update
- Firmware version as a 32 bit unsigned number

By default, we show the ESRT devices as decimal or hexadecimal numbers as different vendors format the number in different ways. When fwupd gets information about how to format the raw version is converts the number into a more familiar form.

When the hardware GUID is static, a quirk may be appropriate, for example:

    [28108d08-5027-42c2-a5b8-92d6ede9b97b]
    VersionFormat = quad

As the GUID may be model specific, the daemon also reads the metadata and copies the version format from that. This means that `fwupdmgr get-devices` may return the UEFI device as a number initially, then once `fwupdmgr refresh` has completed it may start showing the exact same device as `A.B.C.D`, aka `quad` format.

The main formats used by vendors are `triplet`, `quad`, `dell-bios` and `dell-bios-msb`.

    0xAABBCCDD -> 0xAA.0xBB.0xCCCC is `triplet`, used for Lenovo
    0xAABBCCDD -> 0xAA.0xBB.0xCC.0xDD is `quad`, used for HP
    0xAABBCCDD -> 0xBB.0xCC.0xDD is `dell-bios`, used for Dell
    0xAABBCCDD -> 0xAA.0xBB.0xCC is `dell-bios-msb`, used for Dell since CY24

There are more details about firmware version formats and a full list of all the different allowed values on the LVFS.

NOTE: Firmware can require either the `quad` or `triplet` string version format, but it may be more portable to depend on the number — which will also work if the metadata has not been refreshed yet.

## Update Behavior

### Capsule update on-disk

Described in UEFI specification § 8.5.5 - Delivery of Capsules via file on Mass Storage device.

If the firmware supports this, it will be the preferred method of updating on aarch64 platforms. You can explicitly disable it by by modifying DisableCapsuleUpdateOnDisk in `/etc/fwupd/uefi_capsule.conf`.

The spec expects runtime SetVariable to be available in order to enable this feature, we need to set `EFI_OS_INDICATIONS_FILE_CAPSULE_DELIVERY_SUPPORTED` in OsIndications variable to trigger processing of submitted capsule on next reboot. However some firmware implementations (e.g U-Boot), can’t set the variable at runtime, but ignore the variable in next reboot and apply the capsule anyway.

The directory \EFI\UpdateCapsule is checked for capsules only within the EFI system partition on the device specified in the active boot option determine by reference to BootNext variable or BootOrder variable processing. Since setting BootNext, for capsule update on-disk, is not yet implemented, the only available option is place the \EFI\UpdateCapsule within the ESP partition indicated by the current BootOrder. Note that this will be always needed if your firmware doesn’t support SetVariable at runtime (even if BootNext functionality is added).

### Runtime capsule updates

The firmware is deployed when the OS is running, but it is only written when the system has been restarted and the `fwupd*.efi` binary has been run. To achieve this fwupd sets up the EFI `BootNext` variable, creating the new boot entry if required.

## GUID Generation

These devices use the UEFI GUID as provided in the ESRT. Additionally, for the system device the `main-system-firmware` internal flag is also added.

For compatibility with Windows 10, the plugin also adds GUIDs of the form `UEFI\RES_{$(esrt)}`.

## Vendor ID Security

The vendor ID is set from the BIOS vendor, for example `DMI:LENOVO` for all devices that are not marked as supporting Firmware Management Protocol. For FMP device no vendor ID is set.

## Custom EFI System Partition (ESP)

Since version 1.1.0 fwupd will autodetect the ESP if it is mounted on `/boot/efi`, `/boot`, or `/efi`, and UDisks is available on the system. In other cases the mount point of the ESP needs to be manually specified using the option EspLocation in `/etc/fwupd/fwupd.conf`.

Setting an invalid directory will disable the fwupd plugin.

## Quirk Use

This plugin uses the following plugin-specific quirks:

### `Flags=cod-indexed-filename`

Use a Capsule-on-Disk filename of `CapsuleUpdateFileXXXX.bin` rather than including the ESRT GUID. This alternative format may be needed for some early InsydeH2O firmwares.

## External Interface Access

This plugin requires:

- read/write access to the EFI system partition.
- read access to `/sys/firmware/efi/esrt/`
- read access to `/sys/firmware/efi/fw_platform_size`
- read/write access to `/sys/firmware/efi/efivars`

## Version Considerations

This plugin has been available since fwupd version `0.8.0` but was renamed to the current name in `1.5.5`.