Applications written in low-level languages without type or memory safety are especially prone to memory corruption. Attackers gain code execution capabilities through such applications despite all currently deployed defenses by exploiting memory corruption vulnerabilities. Control-Flow Integrity (CFI) is a promising defense mechanism that restricts open control-flow transfers to a static set of well-known locations. We present Lockdown, an approach to dynamic CFI that protects legacy, binary-only executables and libraries. Lockdown adaptively learns the control-flow graph of a running process using information from a trusted dynamic loader. The sandbox component of Lockdown restricts interactions between different shared objects to imported and exported functions by enforcing fine-grained CFI checks. Our prototype implementation shows that dynamic CFI results in low performance overhead.
We present new techniques that allow a return-into-libc attack to be mounted on x86 executables that calls no functions at all. Our attack combines a large number of short instruction sequences to build gadgets that allow arbitrary computation. We show how to discover such instruction sequences by means of static analysis. We make use, in an essential way, of the properties of the x86 instruction set.