In this episode, we're diving deep into Apple's groundbreaking Memory Integrity Enforcement (MIE), an unprecedented effort poised to redefine the landscape of mobile security, and we'll also explore the broader spectrum of threats targeting the iOS ecosystem.

Apple's Memory Integrity Enforcement (MIE) is the culmination of a half-decade of intensive design and engineering, combining the unique strengths of Apple silicon hardware with advanced operating system security. Apple believes MIE represents the most significant upgrade to memory safety in the history of consumer operating systems. This comprehensive, always-on protection is designed to provide industry-first memory safety across Apple devices, all without compromising device performance.

The Driving Force: Combating Mercenary Spyware While the iPhone has never experienced a successful, widespread malware attack, Apple's focus for MIE is primarily on the mercenary spyware and surveillance industry. These highly sophisticated threats, often associated with state actors, utilize exploit chains that can cost millions of dollars to target a small number of specific individuals. A common denominator in these advanced attacks, whether targeting iOS, Windows, or Android, is their reliance on memory safety vulnerabilities. MIE aims to disrupt these highly effective exploitation techniques that have been prevalent for the last 25 years.

How MIE Works: A Three-Pronged Defense MIE is built on a robust foundation of hardware and software innovations:
1. Secure Memory Allocators: Apple's efforts in memory safety include developing with safe languages like Swift and deploying mitigations at scale. Key to MIE are its secure memory allocators, such as kalloc_type (introduced in iOS 15 for the kernel) and xzone malloc (for user-level in iOS 17), alongside WebKit's libpas. These allocators use type information to organize memory, thwarting attackers' goals of creating overlapping interpretations of memory to exploit use-after-free and out-of-bounds bugs.
2. Enhanced Memory Tagging Extension (EMTE): Building on Arm's 2019 Memory Tagging Extension (MTE) specification, Apple conducted deep evaluations and collaborated with Arm to address weaknesses, leading to the Enhanced Memory Tagging Extension (EMTE) specification in 2022. MIE rigorously implements EMTE in strictly synchronous, always-on mode, a crucial factor for real-time defensive measures in adversarial contexts. EMTE prevents common memory corruption types:
    ◦ Buffer Overflows: The allocator tags neighboring allocations with different secrets. If memory access spills over into an adjacent allocation with a different tag, the hardware blocks it, and the operating system can terminate the process.
    ◦ Use-After-Free Vulnerabilities: Memory is retagged when reused. If a request uses an older, invalid tag for retagged memory, the hardware blocks it. EMTE also specifies that accessing non-tagged memory from a tagged region requires knowing that region’s tag, making it harder for attackers to bypass EMTE.
3. Tag Confidentiality Enforcement: This critical component protects the implementation of Apple's secure allocators and the confidentiality of EMTE tags, even against side-channel and speculative-execution attacks. Apple's silicon implementation prevents tag values from influencing speculative execution, a vulnerability seen in other MTE implementations. Furthermore, MIE addresses Spectre variant 1 (V1), a speculative-execution vulnerability, with a mitigation designed for virtually zero CPU cost, making it impractical for attackers to leak tag values and guide attacks.
Impact and Availability Memory Integrity Enforcement is built right into Apple hardware and software in all iPhone 17 and iPhone Air models, offering unparalleled, always-on...