Gray Hat Hacking, Second Edition, 2nd Edition

User Space Shellcode

The majority of programs that typical computer users interact with are said to run in user space. User space is that portion of a computer’s memory space dedicated to running programs and storing data that has no need to deal with lower level system issues. That lower level behavior is provided by the computer’s operating system, much of which runs in what has come to be called kernel space, since it contains the core, or kernel, of the operating system code and data.

System Calls

Programs that run in user space and require the services of the operating system must follow a prescribed method of interacting with the operating system, which differs from one operating system to another. In generic terms, we say that user programs ...