Few storage technology such is EMMC, UFS, and NVMe support RPMB
hardware partition with common protocol and frame layout.
The RPMB partition cannot be accessed via standard block layer, but
by a set of specific commands: WRITE, READ, GET_WRITE_COUNTER, and
PROGRAM_KEY.
Such a partition provides authenticated and replay protected access,
hence suitable as a secure storage.
A storage device registers its RPMB hardware (emmc) partition or
RPMB W-LUN (ufs) with the RPMB layer providing an implementation for
send_rpmb_req() handler.
Tere is as well simulation platform device. This is handy as an RPMB
key can be programmed only once at storage device lifetime.
The RPMB layer aims to provide in-kernel API for Trusted Execution
Environment (TEE) devices that are capable to securely compute block
frame signature. A TEE driver can claim rpmb interface, for example,
via class_interface_register ().