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Execute Disable (NX)

Architecture referenceFeex

Execute Disable, wey dem still dey call NX or XD for x86 language, dey allow page table dem make dem mark memory as non-executable. Na hardware foundation piece wey operating-system execution-protection policy dem dey use.

Wetin you need know

Execute Disable, wey dem still dey call NX or XD for x86 language, dey allow page table dem make dem mark memory as non-executable. Na hardware foundation piece wey operating-system execution-protection policy dem dey use.

How e dey work

Wen dem enable am for di right paging environment, instruction wey fetch from page wey dem mark non-executable go cause fault instead of make e run di byte dem. Page permission dey separate execution from data access; software na im get di work to assign correct permission and manage change for proper generated code.

Where e dey useful

OS fit map data buffer without execution permission so dat writing machine-code byte dem enter dat buffer no go make am executable code page. JIT runtime dem dey use standard memory-management API dem and permission policy dem for code wey dem generate.

How to check support and enablement

CPUID.80000001H:EDX bit 20 dey list di x86 execute-disable capability under di vendor rule wey apply. Di actual enforcement still depend on di paging mode and how OS enable am. Check di OS protection status wey dem document instead of to assume am from CPU model.

Capability, enablement and enforcement na different ting dem wey person must check separately. Processor fit support protection while di OS, application or virtual-machine policy no turn am on. Database support field no be attestation say running system dey secure.

Wetin di feature no dey guarantee

NX no dey prove say executable file dey safe, e no dey block every code-reuse attack, and e no dey prove say Windows go work. Data still fit dey readable or writable according to separate permission dem. Feature flag no mean say every memory mapping dey follow tight write/execute policy.

Compatibility and performance inside real life

Keep di OS, firmware and affected runtime current. If protection show compatibility problem, make you use vendor diagnostics and supported update dem first. Broad protection toggle fit affect oda application dem wey no concern am, so e suppose follow clear deployment and recovery policy.

Practical verification checklist

  1. Record di exact processor or platform model plus di application, OS and runtime version dem wey dey involve. Make you keep di exact word dem wey di error or requirement use.
  2. Check di manufacturer reference for dat exact model, den inspect di real capability and enabled state inside di environment where di program dey run.
  3. Compare every single requirement of di binary or backend wey you choose. Name wey resemble am, alias, or broad technology label no reach.
  4. Confirm say di application select di implementation wey dem intend. Use di diagnostics wey dem document and supported fallback if requirement dem no complete.
  5. Make only one supported change at a time, den run di same workload again. Keep di original configuration and recovery way ready.

If dem list di feature but software no fit use am

Start from di exact component wey dey fail. Hardware database dey describe capability wey dem record; di operating system or hypervisor fit show different real environment. If illegal-instruction error happen, you still need to check di exact instruction wey cause di fault and di binary build, because corrupt file or anoda instruction wey no dey supported fit give di same kind problem.

Install di application, driver or runtime version wey get support for dat exact platform, and use di vendor documented baseline or fallback build if e need am. Software update no fit create instruction wey di processor no get. Firmware and security-policy change dem suppose follow di system manufacturer procedure and recovery plan, no be just any common optimization advice.

Sources and scope of dis explanation

Intel 64 and IA-32 Architectures Software Developer's Manual

Dis reference dem establish architectural behavior and software requirement dem. Dem no dey independently verify every feature value for any linked hardware model page. For model support, use dat page manufacturer evidence and check di active system configuration. Dis article no supply benchmark, certification or independent review date.

Sources and verification

Editorial ownership: Feex. No independent review date dey recorded. How we dey do research.

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