Enhancing Server Availability and Security Through Failure-Oblivious Computing

We present a new technique, failure-oblivious computing, that enables servers to execute through memory errors without memory corruption. Our safe compiler for C inserts checks that dynamically detect invalid memory accesses. Instead of terminating or throwing an exception, the generated code simply discards invalid writes and manufactures values to return for invalid reads, enabling the server to continue its normal execution path. We have applied failure-oblivious computing to a set of widely-used servers from the Linux-based open-source computing environment. Our results show that our techniques 1) make these servers invulnerable to known security attacks that exploit memory errors, and 2) enable the servers to continue to operate successfully to service legitimate requests and satisfy the needs of their users even after attacks trigger their memory errors. We observed several reasons for this successful continued execution. When the memory errors occur in irrelevant computations, failure-oblivious computing enables the server to execute through the memory errors to continue on to execute the relevant computation. Even when the memory errors occur in relevant computations, failure-oblivious computing converts requests that trigger unanticipated and dangerous execution paths into anticipated invalid inputs, which the error-handling logic in the server rejects. Because servers tend to have small error propagation distances (localized errors in the computation for one request tend to have little or no effect on the computations for subsequent requests), redirecting reads that would otherwise cause addressing errors and discarding writes that would otherwise corrupt critical data structures (such as the call stack) localizes the effect of the memory errors, prevents addressing exceptions from terminating the computation, and enables the server to continue on to successfully process subsequent requests. The overall result is a substantial extension of the range of requests that the server can successfully process.