Architectural support for shadow memory in multiprocessors

Abstract

Runtime monitoring support serves as a foundation for the important tasks of providing security, performing debugging, and improving performance of applications. Often runtime monitoring requires the maintenance of information associated with each of the application's original memory location, which is held in corresponding shadow memory locations. Unfortunately, existing robust shadow memory implementations are inefficient. In this paper, we present a shadow memory implementation that is both efficient and robust. A combination of architectural support (in the form of ISA support and augmentations to the cache coherency protocol) and operating system support (in the form of coupled allocation of memory pages used by the application and associated shadow memory pages) is proposed. By coupling the coherency of shadow memory with the coherency of the main memory, we ensure that the shadow memory instructions execute atomically with their corresponding original memory instructions. Our page allocation policy enables fast translation of original addresses into corresponding shadow memory addresses; thus allowing implicit addressing of shadow memory. This approach obviates the need for page table entries for shadow pages. Our experiments show that the overheads of runtime monitoring tasks are significantly reduced in comparison to previous software implementations.