iDEA: Static Analysis on the Security of Apple Kernel Drivers

Drivers on Apple OSes (e.g., iOS, tvOS, iPadOS, macOS, etc.) run in the kernel space and driver vulnerabilities can incur serious security consequences. A recent report from Google Project Zero shows that driver vulnerabilities on Apple OSes have been actively exploited in the wild. Also, we observed that driver vulnerabilities have accounted for one-third of kernel bugs in recent iOS versions based on Apple's security updates. Despite the serious security implications, systematic static analysis on Apple drivers for finding security vulnerabilities has never been done before, not to mention any large-scale study of Apple drivers.

In this paper, we developed the first automatic, static analysis tool iDEA for finding bugs in Apple driver binaries, which is applicable to major Apple OSes (iOS, macOS, tvOS, iPadOS). We summarized and tackled a set of Apple-unique challenges: for example, we show that prior C++ binary analysis techniques are ineffective (i.e., failing to recover C++ classes and resolve indirect calls) on Apple platform due to Apple's unique programming model. To solve the challenges, we found a reliable information source from Apple's driver programming and management model to recover classes, and identified the unique paradigms through which Apple drivers interact with user-space programs. iDEA supports customized, pluggable security policy checkers for its security analysis. Enabled by iDEA, we performed the first large-scale study of 3,400 Apple driver binaries across major Apple OSes and 15 OS versions with respect to two common types of security risks - race condition and out-of-bound read/write, and discovered 35 zero-day bugs. We developed PoC and end-to-end attacks to demonstrate the practical impacts of our findings. A portion of the bugs have been patched by recent Apple security updates or are scheduled to be fixed; others are going through Apple's internal investigation procedure. Our evaluation showed that iDEA incurs a low false-positive rate and time overhead.