Experimenting with CHERI on the Sonata Board

The CHERI extension for RISC-V provides a promising way of designing fundamentally secure systems. I introduced this back in November 2023, but at the time there was no easy hardware to work with. This article introduces the open-source hardware (OSHW) Sonata board, which lets you experiment with CHERIot on a more user-friendly platform.

- By Colin O'Flynn

FIGURE 1 An overview of the Sonata Board

Back in my November 2023 article in Issue #400 of Circuit Cellar I introduced you to the CHERI and CHERIot architecture, which I presented as a promising way of securing your existing C/C++ code with minimal effort. At the time, I lamented that it was difficult to “get started” with CHERIot, as it required you to build your own soft-core processor.

Since then, the Sunburst Project has released a board with prebuilt FPGA images, called the Sonata Board. While it’s still not as cheap as a simple microcontroller development kit, it has a similar development flow, only requiring you to compile code for the target. The project provides reference code, and the physical platform can be expanded with a variety of add-on boards (shields).

In this article, I'll quickly remind you of what CHERIot is, before showing you how you could use this with the physical system. The physical board is something I helped design, but the real effort behind Sonata is the FPGA work and the reference platform, which was developed by a team at lowRISC. The physical board is fully open-source, so you can build your own or modify it for specific tasks as you see fit.

FIGURE 2 This diagram shows the various blocks on the Sonata Board, some of which are implemented inside the FPGA in a soft-core microcontroller.

WHAT’S CHERI ALL ABOUT?