STM32MP1-Old-Kits: Using the ST Trusted Platform Module (TPM) Chip with Emcraft Linux BSP for the SoC
1. Overview
This Application Note describes how to use the ST ST33KTPM2X Trusted Platform Module (TPM) with Emcraft Systems' Linux BSP for the STM32MP1 SoC.
The ST33KTPM2X device is a member of the ST STSAFE-TPM (trusted platform module) family of products, which offers a broad portfolio of standardised solutions for embedded, PC, mobile and computing applications. The STSAFE-TPM includes turnkey products compliant with the Trusted Computing Group (TCG) standards that provide services to protect the confidentiality, integrity and authenticity of information and devices. The STSAFE-TPM devices are all Common Criteria (EAL4+) and FIPS certified.
The ST33KTPM2X is a TPM 2.0-compliant device, that is easy to integrate in an embedded design, using the standards-compliant SPI and I2C interfaces to the host SoC, such as the ST STM32MP1. Refer to the following page for detailed information of the ST33KTPM2X module: ST33KTPM2X - STMicroelectronics .
The Emcraft Linux BSP for the STM32MP1 SoC has been enhanced with appropriate device drivers and configuration interfaces allowing seamless integration with the ST33KTPM2X device. This Application Note provides detailed instructions on the steps that are needed to enable software support for the STSAFE-TPM in Linux running on the STM32MP1 SoC.
2. Hardware Platform
The following hardware platform is used by Emcraft to support the ST STSAFE-TPM devices with the STM32MP1 SoC:
The Emcraft STM32MP1 SOM, available in the 800MHz and 650MHz variants. See: STM32MP1 SOM Resource Directory .
The Emcraft STM32MP1-BSB Starter Kit, which provides, among other things, a standards-compliant interface to Click / mikroBUS boards. See STM32MP1 SOM Resource Directory .
The Emcraft TPM-Click Module board, which is a compact Click / mikroBUS add-on board that hosts the ST ST33KTPM2X TPM 2.0-compliant module and provides the standard SPI / I2C interfaces to the host SoC. While Emcraft uses the Click board to illustrate integration with the STM32MP1 SoC, the board can be used with any embedded device that provides a standard Click / mikroBUS interface. See STM32MP1-Old-Kits: TPM-Click Module Hardware User’s Guide .
3. Software Platform
The following hardware platform is used by Emcraft to support the ST STSAFE-TPM devices with the STM32MP1 BSP (Board Support Package):
Kernel space device drivers. While the generic TPM2 support is enabled by
CONFIG_TCG_TPM
configuration parameter, Emcraft's TPM-Click Module board support is enabled byCONFIG_TCG_TIS_I2C
configuration parameter (making the I2C bus the default transport to the host). These configuration parameters enable building of the TPM2 drivers in the Linux kernel and reside in thedrivers/char/tpm
directory in the kernel source tree. The aforementioned drivers are enabled in the Emcraft BSP by default.User-space TPM stack including the
cryptsetup
utility in thesystemd
software suite,tpm2-tools
set of utilities (version 5.5), andtpm2-tss
shared library (version 4.0.1). The user space TPM stack is a part of the https://git.yoctoproject.org/git/meta-security Yocto layer.
4. Building STM32MP1 Images for STSAFE-TPM
Step through the following procedure to activate support for the STSAFE-TPM in the Emcraft BSP:
Prepare the Linux build host. See Linux PC requirements PC prerequisites - stm32mpu.
On the build host, set up the OpenSTLinux release 5.0.0 sources:
[psl@sergmir openstlinux]$ curl https://storage.googleapis.com/\ git-repo-downloads/repo > repo [psl@sergmir openstlinux]$ chmod 755 repo [psl@sergmir openstlinux]$ sudo mv repo /usr/bin [psl@sergmir openstlinux]$ repo init -u \ https://github.com/STMicroelectronics/oe-manifest.git \ -b refs/tags/openstlinux-6.1-yocto-mickledore-mp1-v23.06.21 ... [psl@sergmir openstlinux]$ repo sync ... [psl@sergmir openstlinux]$ ls -l total 4 drwxrwxr-x 7 psl psl 4096 Apr 18 18:37 layers [psl@sergmir openstlinux]$ ls -l layers/ total 20 drwxrwxr-x 14 psl psl 4096 Apr 18 18:37 meta-openembedded drwxrwxr-x 12 psl psl 4096 Apr 18 18:37 meta-qt5 drwxrwxr-x 6 psl psl 4096 Apr 18 18:37 meta-st drwxrwxr-x 6 psl psl 4096 Apr 18 18:37 meta-timesys drwxrwxr-x 9 psl psl 4096 Apr 18 18:37 openembedded-core [psl@sergmir openstlinux]$
Clone the Emcraft meta layer:
[psl@sergmir openstlinux]$ git clone -b linux-stm32mp1-4.1.0 \ git@gitlab.com:emcraft/stm32mp15x/meta-emcraft.git \ layers/meta-st/meta-emcraft ...
Clone the Secutiry meta layer:
[psl@sergmir openstlinux]$ git clone -b mickledore \ https://git.yoctoproject.org/git/meta-security \ layers/meta-security ...
Configure the build (change
stm32mp15-som
tostm32mp157d-som
in the below command for the 800MHz version of the STM32MP1-SOM):The STM32MP1 BSP depends on some packages and firmware covered by a software license agreement (SLA). You will be asked to read and to accept this license.
Enable the
tpm2
adsecurity
features:Run the build:
5. Verifying Support for STSAFE-TPM
5.1. Verifying STSAFE-TPM Configuration
Follow the step-wise procedure below to verify that the TPM module has been recognised and correctly configured on the target:
In the Linux boot-up messages, verify that the TPM driver has probed the TPM device:
Check the TPM version:
Check the TPM capabilities:
5.2. Using STSAFE-TPM for Hardware-Bound Data Encryption
This command sequence showcases how to utilise the STSAFE-TPM to create a hardware-bound encrypted disk. Once the disk has been encrypted, the passphrase to unlock the disk is stored in the TPM’s NV storage, so the unlocking and decryption of the disk is only possible with the specific TPM chip being present on the embedded target.
5.2.1. Phase 1: Disk Creation
This phase creates the disk. Follow the step-wise procedure below:
Create an empty disk image:
Create a TPM-stored sealed key.
Create the loop device for the disk image:
Create a LUKS2-encrypted disk:
Unlock the created disk:
Create the
ext4
file system on the disk.Mount the
ext4
file system:
5.2.2. Phase 2: Verifying Disk Encryption
Now that the encrypted disk is created and the file system is mounted, we can create a file on it and verify if the data is indeed encrypted. Follow the step-wise procedure below:
Create a plain file with some text:
Unmount the file system:
Close the encrypted disk and unbind the loop device:
Search the disk image for the encrypted data. It will not be found:
5.2.3. Phase 3: Disk Unlocking
Once the disk has been created, the sequence to unlock it and mount is as follows:
Bind the loop device to the disk image:
Unlock the encrypted disk:
Mount the file system:
Print the encrypted text file: