CHERI Concentrate: Practical Compressed Capabilities


Type
Article
Change log
Authors
Woodruff, Jonathan 
Joannou, Alexandre 
Fox, Anthony 
Norton, Robert M 
Abstract

We present CHERI Concentrate, a new fat-pointer compression scheme applied to CHERI, the most developed capability-pointer system at present. Capability fat-pointers are a primary candidate for enforcing fine-grained and non-bypassable security properties in future computer systems, although increased pointer size can severely affect performance. Thus, several proposals for capability compression have been suggested but these did not support legacy instruction sets, ignored features critical to the existing software base, and also introduced design inefficiencies to RISC-style processor pipelines. CHERI Concentrate improves on the state-of-the-art region-encoding efficiency, solves important pipeline problems, and eases semantic restrictions of compressed encoding, allowing it to protect a full legacy software stack. We analyze and extend logic from the open-source CHERI prototype processor design on FPGA to demonstrate encoding efficiency, minimize delay of pointer arithmetic, and eliminate additional load-to-use delay. To verify correctness of our proposed high-performance logic, we present a HOL4 machine-checked proof of the decode and pointer-modify operations. Finally, we measure a 50%-75% reduction in L2 misses for many compiled C-language benchmarks running under a commodity operating system using compressed 128-bit and 64-bit formats, demonstrating both compatibility with and increased performance over the uncompressed, 256-bit format.

Description
Keywords
Capabilities, fat pointers, compression, memory safety, computer architecture
Journal Title
IEEE TRANSACTIONS ON COMPUTERS
Conference Name
Journal ISSN
0018-9340
1557-9956
Volume Title
68
Publisher
Institute of Electrical and Electronics Engineers (IEEE)
Rights
All rights reserved
Sponsorship
EPSRC (EP/K503757/1)
Engineering and Physical Sciences Research Council (EP/K008528/1)
Engineering and Physical Sciences Research Council (EP/R012458/1)