Quantitative Analysis of Protection Options

Various mechanisms are available for protecting software services. Some rely on software protection, some on hardware and some on both. There has been much discussion about protection options, but there is surprising little hard data on relative costs. This paper provides detailed measurements of five different protection schemes and quantifies their impact on performance. These measurements lead to five assertions regarding protection. The cost of hardware-based protection is proportional to the number of transitions from the client to the service. For software-based protection, cost is proportional to the number of instructions executed in the service domain. The effect of protection on the memory subsystem is relatively unimportant. The impact of sharing data between client and service is important for sub-page size data granularities but not for larger data granularities. The evolution of technology will favor hardware-based protection schemes over software-based schemes.