Umbra is a lightweight Rust-based kernel designed to wrap binaries into runtime Trusted Execution Environments (TEEs) for TrustZone-M. It provides APIs compliant with the TCG specification as a static library, enabling integration with third-party software such as RTOSes or bare-metal applications to create TEEs dynamically or statically. By leveraging Rust, Umbra minimizes the Trusted Computing Base (TCB) and enhances code safety. Currently, it supports Cortex-M33-based systems, including ST L552 and L562 microcontrollers.
To build Umbra, rust is required
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
Currently, we are using nightly instead of stable. Therefore users are required to
rustup toolchain install nightly
rustup override set nightly
Finally add the Armv8-M mainline target
rustup target add thumbv8m.main-none-eabi
Additional tools required for building and running include the ARM cross-compiler toolchain gcc-arm-none-eabi and the OpenOCD backend. While GDB is used to load the ELF file, the initial flashing configuration for STM32 devices is performed using the STM32 Programmer tool.
Configure all the environmental variables
source settings.sh
Build the secure boot ELF
make secureboot_build
Build the umbra library
Make umbra_build
The static library will be available after build in lib. In order for an application to use umbra, the secure boot must be loaded first on the device.
Second, the host application must include the lib/libumbra.a and using the umbra-defined linker script files.
An example of it is included in host/bare_metal_arm.
Once both host and secure boot are built, flash the device using:
make program_target
At this point it is possible to run the loaded elf using
make run_elf
