DDRMCE internal peripheral

Applicable for

STM32MP13x lines

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1. Article purpose

The purpose of this article is to:

• briefly introduce the DDRMCE peripheral and its main features
• indicate the level of security supported by this hardware block
• explain how to configure the DDRMCE peripheral.

2. Peripheral overview

The DDRMCE (DDR Memory Cipher Engine) peripheral allows to defined one AES encrypted region in DDR memory.

Information

Functions and registers names declared in the embedded software are using "MCE" / "mce" acronym instead of the longest "DDRMCE" / "ddrmce" ones, so take care about this for any research in the code

2.1. Features

Refer to STM32MP13 reference manuals for the complete list of features, and to the software components, introduced below, to know which features are really implemented.
DDRMCE 128-bit master key is provisioned during boot processing, in order to use AES block ciphering feature. It must be fully saved in Backup RAM for low power sequences.

2.2. Security support

DDRMCE is a securable peripheral (under ETZPC control).

3. Peripheral usage and associated software

3.1. Boot time

The DDRMCE, part of the DDR subsystem, is configured inside TF-A BL2 to setup the security of a DDR region. This should be done before accessing DDR region if encryption is required.

3.2. Runtime

3.2.1. Overview

All system bus traffic going through an encrypted region is managed on-the-fly by the DDRMCE, automatically decrypting reads and encrypting writes.

3.2.2. Software frameworks

Domain	Peripheral	Software components		Comment
		OP-TEE	Linux
RAM/Security	DDRMCE	Memory mapping

3.2.3. Peripheral configuration

The DDRMCE configuration is generated via STM32CubeMX tool, according to the region characteristics (address, length, type). This configuration is applied during boot time by the FSBL (see Boot chain overview): TF-A.

3.2.4. Peripheral assignment

Expand

Click on the right to expand the legend...

STM32MP13 internal peripherals

Check boxes illustrate the possible peripheral allocations supported by STM32 MPU Embedded Software:

• ☐ means that the peripheral can be assigned (☑) to the given runtime context.
• ⬚ means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in STM32 MPU Embedded Software distribution.
• ✓ is used for system peripherals that cannot be unchecked because they are statically connected in the device.

Refer to How to assign an internal peripheral to a runtime context for more information on how to assign peripherals manually or via STM32CubeMX.
The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possiblities might be described in STM32MP13 reference manuals.

Domain	Peripheral	Runtime allocation			Comment
		Instance	Cortex-A7 secure (OP-TEE)	Cortex-A7 non-secure (Linux)
Security	DDRMCE	DDRMCE	✓	✓

Doubledata rate (memory domain)

Advanced encryption standard

Random access memory (Early computer memories generally hadserial access. Memories where any given address can be accessed when desired were then called "random access" to distinguish them from the memories where contents can only be accessed in a fixed order. The term is used today for volatile random-acces ssemiconductor memories.)

Trusted firmware for Arm^® Cortex^®-A

Boot loader stage 2

Open portable trusted execution environment

Linux^® is a registered trademark of Linus Torvalds.

First stage boot loader

Cortex^®

Doubledata rate (memory domain)

Advanced encryption standard

Random access memory (Early computer memories generally hadserial access. Memories where any given address can be accessed when desired were then called "random access" to distinguish them from the memories where contents can only be accessed in a fixed order. The term is used today for volatile random-acces ssemiconductor memories.)

Trusted firmware for Arm^® Cortex^®-A

Boot loader stage 2

Open portable trusted execution environment

Linux^® is a registered trademark of Linus Torvalds.

First stage boot loader

Cortex^®

Arm^® is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.