Which term is set in the processor to designate memory areas that cannot execute code at all?

• A. Secure Enclave
• B. ASLR
• C. NX Bit
• D. XN Bit

Answer: (D)

The feature being tested is a memory protection mechanism that marks certain regions as not allowed to run code. This is implemented by a no-execute control bit in the page table entries. When this bit is set for a memory page, the CPU will not fetch or execute instructions from that page, and attempts to do so will trigger a fault. This helps prevent code-injection techniques by ensuring data areas like the stack or heap cannot be executed as code.

XN Bit is the term used for this indicator in some architectures, standing for Execute Never. It serves the same purpose as the NX bit (No-Execute) used in others. So the XN Bit is the correct designation in this context. Secure Enclave and ASLR address layout randomization are related security concepts but do not designate memory areas as non-executable.