Chrome OS RMA shim

Overview

RMA stands for Return Merchandise Authorization. When there’s a problem that the end user cannot solve, the user returns the device to the partner’s service center for diagnosis and repair. The service center may swap components and reinstall the firmware and/or software image. For Chromebooks, that means the service center may need to disable write protection and change the HWID to match the new configuration.

RMA shim

Chromebooks are highly secured. With verified boot and write protection, it’s difficult for the service center to run diagnosis and repair programs (usually built and customized by partners) because those won’t be signed by Google. Service centers may also have limited (or even no) network access. In general, what the partner needs is a tool that fulfills these requirements:

The tool is signed by Google. An operator can boot the device by turning on the developer mode, attaching a USB stick and invoking recovery mode.
The tool can run the partner’s customized tool programs to check and verify components, very similar to the way the factory process works.

The RMA shim image is designed to meet these requirements. An RMA shim image is a combination of existing Chrome OS factory bundle components, all combined into one disk, including:

Factory install shim
Release image (FSI)
Test image
Factory toolkit
HWID bundle
Other optional components (firmware, complete script, etc.)

Universal RMA shim (Multi-board RMA shim)

A problem for regular (single-board) RMA shims is that we have to create separate per-board RMA shims for each project, which makes it hard to manage shim images and physical USB drives. A universal shim contains multiple RMA shims for different boards, which is easier to manage and distribute.

Pros:

Reduce the number of shims to manage.

Cons:

The size of a universal shim can be large. Each board in a shim takes about 3 GB, so a universal shim containing 3 boards will have size 9~10 GB.

Create an RMA shim

To create an RMA shim, you should first get a factory bundle and follow the steps below.

Adjust RMA test list in factory toolkit

RMA test list is different from the test list used in factory manufacture line. For instance, there is no factory server during RMA. Hence, we need another test list for RMA.

The recommended way is to create a test list that inherits generic_rma.test_list.json, which already takes care of general RMA settings such as disabling factory server and enabling rma_mode, and then add factory tests to RMAFFT group.

{
  "inherit": [
    "generic_rma.test_list"
  ],
  "label": "RMA Test List for <project>",
  "definitions": {
    "RMAFFT": {
      "subtests": [
        ...
        ...
      ]
    }
  }
}

In general, run all factory tests (runin and fatp) in the service centers with reduced test cycles. For example, reduce the duration of the stress test from 4 hours to 10 minutes.
Verify that all spare mainboards used in service centers complete SMT tests.
Verify that all spare mainboards have a registration code that was burned into RW_VPD during the factory process before sending the boards to service centers.
Discuss with the OEM to finalize test items for the RMA process.
Do not modify or remove any GRT (Google Required Test) items.
Make sure the firmware write protection is enabled (which should be true if constants.phase is set to PVT).

Combine factory bundle components into an RMA shim image

After getting all the bundle components ready, we can combine these components into a single RMA shim image.

image_tool is a useful tool to manage RMA shims. To create an RMA shim image from a factory bundle, use image_tool rma-create command:

$ ./setup/image_tool rma-create \
    --board=BOARD \
    --factory_shim=path/to/factory_install_shim.bin \
    --test_image=path/to/chromiumos_test_image.bin \
    --toolkit=path/to/install_factory_toolkit.run \
    --release_image=path/to/chromiumos_image.bin \
    --hwid=path/to/hwid_bundle.sh \
    --output=rma_image.bin

The command can be simplified if all the components are put in their respective bundle directories (release_image/, test_image/, etc.):

$ ./setup/image_tool rma-create \
    --board=BOARD \
    --output=rma_image.bin

Use an RMA shim

Flash the rma_image.bin to a USB drive, boot it with developer switch enabled in recovery mode (see following steps), and then the device will boot from the RMA shim.

Flash an image to USB drive

Use dd command to flash a shim image to a USB drive or SD card, replacing /dev/sdX with the name of the USB/SD device.

$ sudo dd if=rma_image.bin of=/dev/sdX bs=8M iflag=fullblock oflag=dsync

If you have a Chromium OS development environment, you can also use cros flash command in chroot.

$ cros flash usb:// rma_image.bin

Boot from RMA shim (clamshells / convertibles)

Press ESC + F3(REFRESH) + POWER to enter recovery mode
Press CTRL + D to turn on developer switch
Press ENTER to confirm
Press ESC + F3(REFRESH) + POWER to enter recovery mode again (no need to wait for wiping)
Insert and boot from USB stick with rma_image.bin

Boot from RMA shim (tablets / detachables)

Press POWER + VOL_UP + VOL_DOWN for at least 10 seconds, and release them to enter recovery mode
Press VOL_UP + VOL_DOWN to show recovery menu
Press VOL_UP or VOL_DOWN to move the cursor to “Confirm Disabling OS Verification”, and press POWER to select it
Press POWER + VOL_UP + VOL_DOWN for at least 10 seconds, and release them to enter recovery mode again (no need to wait for wiping)
Insert and boot from USB stick with rma_image.bin

The RMA shim has a menu that allows the user to select an action to perform, which is described in Factory Installer README. Moreover, if the RMA shim is created using image_tool rma-create command, the tool adds a flag RMA_AUTORUN=1 in lsb-factory file, which sets the default action of the menu depending on the cr50 version and hardware write protect status, such that:

If hardware write protection is enabled, and cr50 version is older than the cr50 image in the shim, set the default action to (U) Update cr50. After cr50 is updated, the device will reboot. The user should enter recovery mode and boot to shim again.
If hardware write protection is enabled, and cr50 version is not older than the cr50 image in the shim, set the default action to (E) Reset Cr50, also known as RSU (RMA Server Unlock) to disable hardware write protect and enter factory mode. After RMA reset, the device will reboot. The user should enter recovery mode and boot to shim again.
If hardware write protection is disabled, set the default action to (I) install to install payloads from USB. If hardware write protect is disabled by disconnecting the battery instead of doing RSU, the install script will also enable factory mode at the end of installation.

You can stop the default action and return to shim menu by pressing any key within 3 seconds when the console prompts “press any key to show menu instead”.

During installation, you can remove the RMA shim when the copy is complete (the text color changes from yellow to green). After the installation, the device will boot into the test image with factory toolkit. Run through the factory tests to complete the flow. The last test should wipe out the factory test image and enable the release image.

Create a universal RMA shim

We can use image_tool rma-merge to create a universal shim using multiple RMA shims.

$ ./setup/image_tool rma-merge \
    -i soraka.bin scarlet.bin \
    -o universal.bin

To delete a previously generated output image, specify the -f option:

$ ./setup/image_tool rma-merge \
    -i soraka.bin scarlet.bin \
    -o universal.bin -f

Use a universal RMA shim

Using a universal RMA shim is exactly the same as using a normal single-board RMA shim. Flash the image to a USB drive and boot from it using the instructions mentioned above.

Other RMA commands

There are other image_tool commands that makes verifying and modifying RMA shims easier.

Print bundle components in an RMA shim

image_tool rma-show command prints the component versions in an RMA shim.

$ ./setup/image_tool rma-show rma_image.bin
This RMA shim contains boards: soraka
-------------------------
board        : soraka
install_shim : 10323.39.24
release_image: 10575.37.0 (Official Build) dev-channel soraka
test_image   : 10323.39.24 (Official Build) dev-channel soraka test
toolkit      : soraka Factory Toolkit 10323.39.24
firmware     : Google_Soraka.10431.32.0;Google_Soraka.10431.48.0
hwid         : None
complete     : None
-------------------------

This command also applies to universal RMA shim.

$ ./setup/image_tool rma-show universal.bin
This RMA shim contains boards: soraka scarlet
-------------------------
board        : soraka
install_shim : 10323.39.24
release_image: 10575.37.0 (Official Build) dev-channel soraka
test_image   : 10323.39.24 (Official Build) dev-channel soraka test
toolkit      : soraka Factory Toolkit 10323.39.24
firmware     : Google_Soraka.10431.32.0;Google_Soraka.10431.48.0
hwid         : None
complete     : None
-------------------------
board        : scarlet
install_shim : 10211.54.0
release_image: 10575.67.0 (Official Build) stable-channel scarlet
test_image   : 10211.53.0 (Official Build) dev-channel scarlet test
toolkit      : scarlet Factory Toolkit 10211.53.0
firmware     : Google_Scarlet.10388.26.0
hwid         : None
complete     : None
-------------------------