Secure Page Table Monitor

SPTM (Secure Page Table Monitor) is a vital hardware feature found in Apple's A15 and later processors, revolutionizing memory management and access control in iOS from version 17 onward. It replaces the conventional Page Protection Layer (PPL) with a more robust approach to system security.

Operation: SPTM operates within the Guest Level 1 (GL1) or Guest Level 2 (GL2) of the system architecture, overseeing page tables. These tables are essential data structures that map virtual memory addresses to physical ones, crucial for memory management.

Hardware-Level Enforcement: SPTM functions at the hardware level, providing direct oversight of memory management operations and access permissions. This hardware-based approach enhances security by reducing vulnerabilities associated with software-based methods.

System Calls: SPTM introduces three system calls for the kernel and privileged processes, enhancing control and responsiveness:

1. SVC #0 (To Be Determined): The purpose of this system call is undisclosed, potentially reserved for future functionalities or specific security operations, adding adaptability to the system. 2. SVC #37: Enable All Interrupts: This call enables all interrupts, aiding system responsiveness for handling asynchronous events and maintaining stability. 3. SVC #38: Disable All Interrupts: Conversely, this call deactivates all interrupts, ensuring uninterrupted execution of critical operations to prevent potential disruptions.

Unfortunately, SPTM significantly raises the bar for jailbreaking on iOS devices equipped with A15 and later processors starting from iOS 17. This is due to tighter control over system calls; as explained above, SPTM introduces specific system calls (such as SVC #0) with undisclosed purposes. These calls might be utilized for future security enhancements or functionalities.

By keeping these functionalities hidden or restricted, Apple can effectively limit the options available for potential jailbreak exploits. Additionally, the system calls provided by SPTM (such as enabling or disabling interrupts) can further bolster the system's resilience against tampering attempts.