Picking a CHERI Allocator: Security and Performance Considerations

Several open-source memory allocators have been ported to CHERI, a hardware capability platform. In this paper we examine the security and performance of these allocators when run under CheriBSD on Arm's experimental Morello platform. We introduce a number of security attacks and show that all but one allocator are vulnerable to some of the attacks - including the default CheriBSD allocator. We then show that while some forms of allocator performance are meaningful, comparing the performance of hybrid and pure capability (i.e. 'running in non-CHERI vs. running in CHERI modes') allocators does not appear to be meaningful. Although we do not fully understand the reasons for this, it seems to be at least as much due to factors such as immature compiler toolchains as it is due to the effects of capabilities on hardware.