Operating System Security and Access Control

Every operating system, whatever its particular design, has to solve the same basic security problem: multiple processes and, often, multiple users share the same hardware, and the operating system must prevent one from interfering with or spying on another while still allowing legitimate work to happen. The foundational mechanism for this is the separation between kernel mode, where the operating system's core code runs with full hardware access, and user mode, where ordinary applications run with restricted privileges and must request services from the kernel through defined system calls. On top of this separation, operating systems layer authentication (verifying who a user is), authorization (determining what that verified user is allowed to do), and process isolation (ensuring one running program cannot read or modify another program's memory without permission). These fundamentals matter because nearly every category of OS-level attack — privilege escalation, unauthorized data access, malware persistence — represents some failure or bypass of one of these basic separations, whether through a software defect, a misconfiguration, or a user granted more trust than their role required.