Memory safety bugs continue to be a major source of security vulnerabilities, with their root causes ingrained in the industry:
the C and C++ systems programming languages that do not enforce memory protection, and the huge legacy codebase written in them that we depend on;
the legacy design choices of hardware that provides only coarse-grain protection mechanisms, based on virtual memory; and
test-and-debug development methods, in which only a tiny fraction of all possible execution paths can be checked, leaving ample unexplored corners for exploitable bugs.
Over the last twelve years, the CHERI project has been working on addressing the first two of these problems by extending conventional hardware Instruction-Set Architectures (ISAs) with new architectural features to enable fine-grained memory protection and highly scalable software compartmentalisation, prototyped first as CHERI-MIPS and CHERI-RISC-V architecture designs and FPGA implementations, with an extensive software stack ported to run above them.
The academic experimental results are very promising, but achieving widespread adoption of CHERI needs an industry-scale evaluation of a high-performance silicon processor implementation and software stack. To that end, Arm have developed Morello, a CHERI-enabled prototype architecture (extending Armv8.2-A), processor (adapting the high-performance Neoverse N1 design), system-on-chip (SoC), and development board, within the UKRI Digital Security by Design (DSbD) Programme (see our earlier blog post on Morello). Morello is now being evaluated in a range of academic and industry projects.
However, how do we ensure that such a new architecture actually provides the security guarantees it aims to provide? This is crucial: any security flaw in the architecture will be present in any conforming hardware implementation, quite likely impossible to fix or work around after deployment.
For the last ten years, SRI International and the University of Cambridge have been working to develop CHERI (Capability Hardware Enhanced RISC Instructions), a DARPA-sponsored processor architecture security technology implementing efficient fine-grained memory protection and scalable software compartmentalization. You can learn more about CHERI in our Introduction to CHERI technical report, which describes the architectural, microarchitectural, formal modelling, and software approaches we have created.
For the last six of those years, we have been collaborating closely with Arm to create an adaptation of CHERI to the ARMv8-A architecture, which is slated to appear in Arm’s prototype Morello processor, System-on-Chip (SoC), and board in Q1 2022. Richard Grisenthwaite, Arm’s Principal Architect, announced this joint work at the UKRI Digital Security by Design (DSbD) workshop in September 2019. DSbD is a UKRI / Industrial Strategy Challenge Fund (ISCF) research programme contributing to the creation of the Morello board, and CHERI is the Digital Security by Design Technology that underlies the programme. Our collaboration with Arm has been an enormously exciting experience, involving daily engagement Arm’s architects, microarchitects, and software designers. This included hosting several members of Arm’s team at our lab in Cambridge over multiple years, as we brought together our long-term research on architectural and software security with their experience in industrial architecture, processor designs, and transition.
For this first developer preview release, we have focused on bringing CHERI C/C++ memory protection to Morello. Our CheriABI process environment, which allows the full UNIX userspace to run with fine-grained spatial memory safety, is fully functional on Morello. This work has been the recent subject of a report from the Microsoft Security Response Center (MSRC), Microsoft’s internal red team and security response organization, describing how CHERI has to potential to deterministically prevent over 2/3 of critical Microsoft software security vulnerabilities. CheriBSD/Morello brings that work over from our research CHERI-MIPS and CHERI-RISC-V platforms to Arm’s Morello. We demonstrated CheriBSD/Morello mitigating several memory-safety vulnerabilities in the EPSRC Digital Security by Design (DSbD) workshop yesterday, talking to 9 UK universities that have been funded to do research building on CHERI and Morello.
We have an aggressive planned quarterly release schedule through the end of 2021 when a full release will ship alongside the Morello board, adapting various CheriBSD security features to Morello:
Userspace heap temporal memory safety based on Cornucopia (in collaboration with Microsoft Research).
Userspace software compartmentalization based on the CHERI co-process model.
Userspace software compartmentalization based on a run-time linker model.
Any updates required to operate well on the shipping Morello board.
CHERI software stack – working release schedule for 2020-2021
Getting started with CheriBSD/Morello is easy (if you have a tolerance for experimental architectural simulators, experimental operating systems, and experimental compilers!). Visit our CHERI Morello software web page to learn more about this work, and then our CheriBSD/Morello distribution page to download our build environment. You can automatically install Arm’s FVP, cross-develop in our docker-based SDK on macOS or Linux, and SSH into the simulated host to try things out.
CHERI is the work of a large research team at SRI International and the University of Cambridge, as well as numerous industrial collaborators at Arm, Google, Microsoft, and elsewhere. My co-investigators, Peter G. Neumann (SRI), Simon W. Moore (Cambridge), Peter Sewell (Cambridge), and I are immensely grateful for their contributions: CHERI would simply not have been possible without your collective effort – thank you! We are also grateful to our sponsors over an extended period, including DARPA, UKRI, Google, and Arm.
We’re delighted to announce that the new security lectureship we advertised has been offered to Alice Hutchings, and she’s accepted. We had 52 applicants of whom we shortlisted three for interview.
Alice works in the Cambridge Cybercrime Centre and her background is in criminology. Her publications are here. Her appointment will build on our strengths in research on cybercrime, and will complement and extend our multidisciplinary work in the economics and psychology of security.