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Interview question · Systems, OS & Memory Safety

Why do JIT compilers clash with W^X memory protection, how do runtimes reconcile them, and why are JIT bugs so valuable to attackers?

W^X says memory is writable or executable, never both. A JIT compiler's whole job is writing code and then running it. How a runtime squares that circle decides how much an attacker gains from a memory bug.

hardNewPreparation tags: Google, Apple, MicrosoftUpdated Nov 2026

W^X says memory is writable or executable, never both. A JIT compiler's whole job is writing code and then running it. How a runtime squares that circle decides how much an attacker gains from a memory bug.

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What if · the follow-ups in this answer

The answer works through 6 follow-ups like an interviewer would

A JavaScript engine compiles code at runtime into machine instructions, which conflicts with policies that forbid writable and executable memory.

  1. What is write xor execute (W^X)?
  2. Why do JIT compilers conflict with it?
  3. How do engines reconcile JIT with W^X?
  4. What do stricter platforms do?
  5. Why do some browsers offer JIT-less modes?
  6. How would you explain the trade-off?

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UP NEXT ON YOUR JOURNEY
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