What Cannot Be Read, Cannot Be Leveraged? Revisiting Assumptions of JIT-ROP Defenses

Despite numerous attempts to mitigate code-reuse attacks, Return-Oriented Programming (ROP) is still at the core of exploiting memory corruption vulnerabilities. Most notably, in JIT-ROP, an attacker dynamically searches for suitable gadgets in executable code pages, even if they have been randomized. JIT-ROP seemingly requires that (i) code is readable (to find gadgets at run time) and (ii) executable (to mount the overall attack). As a response, Execute-no-Read (XnR) schemes have been proposed to revoke the read privilege of code, such that an adversary can no longer inspect the code after finegrained code randomizations have been applied. We revisit these "inherent" requirements for mounting JIT-ROP attacks. We show that JIT-ROP attacks can be mounted without ever reading any code fragments, but instead by injecting predictable gadgets via a JIT compiler by carefully triggering useful displacement values in control flow instructions. We show that defenses deployed in all major browsers (Chrome, MS IE, Firefox) do not protect against such gadgets, nor do the current XnR implementations protect against code injection attacks. To extend XnR's guarantees against JIT-compiled gadgets, we propose a defense that replaces potentially dangerous direct control flow instructions with indirect ones at an overall performance overhead of less than 2% and a code-size overhead of 26% on average.