This commit describe the procedure to configure lowest supported version in the device tree for anti-rollback protection.
Signed-off-by: Masahisa Kojima masahisa.kojima@linaro.org --- Newly created in v6
doc/develop/uefi/uefi.rst | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index efab0fc7b1..f1f13bb993 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -539,6 +539,38 @@ since FMP protocol handles multiple image indexes. [--fit | --raw | --guid <guid-string] \ <image_blob> <capsule_file_name>
+Anti-rollback Protection +~~~~~~~~~~~~~~~~~~~~~~~~ + +The anti-rollback protection is implemented differently from firmware versioning. +U-Boot implements the file-based EFI variable storage, it can be tampered +and not the right place to store the lowest supported version. +U-Boot uses device tree to store the lowest supported version, it is secured +as long as dtb is authenticated together with U-Boot image by the authenticated +capsule update, and the former stage boot loader verifies the image containing the dtb +when the system boots. + +1. Insert the lowest supported version into a device tree + +.. code-block:: console + + $ dtc -@ -I dts -O dtb -o version.dtbo version.dts + $ fdtoverlay -i orig.dtb -o new.dtb -v version.dtbo + +where version.dts looks like:: + + /dts-v1/; + /plugin/; + &{/} { + firmware-version { + image1 { + image-type-id = "09D7CF52-0720-4710-91D1-08469B7FE9C8"; + image-index = <1>; + lowest-supported-version = <3>; + }; + }; + }; + Executing the boot manager ~~~~~~~~~~~~~~~~~~~~~~~~~~