1. Article purpose[edit source]
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[edit source]
The DDRMCE (DDR Memory Cipher Engine) peripheral allows to defined one AES encrypted region in DDR memory.
2.1. Features[edit source]
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[1] block ciphering feature. It must be fully saved in Backup RAM for low power sequences.
2.2. Security support[edit source]
DDRMCE is a securable peripheral (under ETZPC control).
3. Peripheral usage and associated software[edit source]
3.1. Boot time[edit source]
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[edit source]
3.2.1. Overview[edit source]
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[edit source]
| Domain | Peripheral | Software components | Comment | |
|---|---|---|---|---|
| OP-TEE | Linux | |||
| RAM/Security | DDRMCE | Memory mapping | ||
3.2.3. Peripheral configuration[edit source]
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[edit source]
Click on the right to expand the legend...
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 | ✓ | ✓ | |
4. References[edit source]
Arm® is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere. 