Strengthening software self-checksumming via self-modifying code

Recent research has proposed self-checksumming as a method by which a program can detect any possibly mali-cious modification to its code. Wurster et al. developed an attack against such programs that renders code modifica-tions undetectable to any self-checksumming routine. The attack replicated pages of program text and altered values in hardware data structures so that data reads and instruc-tion fetches retrieved values from different memory pages. A cornerstone of their attack was its applicability to a variety of commodity hardware: they could alter memory accesses using only a malicious operating system. In this paper, we show that their page-replication attack can be detected by self-checksumming programs with self-modifying code. Our detection is efficient, adding less than 1 microsecond to each checksum computation in our experiments on three processor families, and is robust up to attacks using either costly interpretive emulation or specialized hardware. 1