Microsoft Change Removed From Linux Over Intel CPU Issues

Arthur T Knackerbracket has processed the following story:

Intel and AMD engineers have stepped in at the eleventh hour to deal with a code contribution from a Microsoft developer that could have broken Linux 6.13 on some systems.

The change, made in the autumn, was a useful improvement at face value. It was a modification to Linux x86_64 to use large read-only execute (ROX) pages for caching executable pages. The theory was that the alteration would result in increased performance.

However, the code caused problems on some setups and an urgent patch from Intel's Peter Zijlstra was committed yesterday to disable it. The stable release of the 6.13 kernel was due this coming weekend.

Zijlstra wrote: "The whole module_writable_address() nonsense made a giant mess of alternative.c, not to mention it still contains bugs -- notable (sic) some of the CFI variants crash and burn.

Control Flow Integrity (CFI) is an anti-malware technology aimed at preventing attackers from redirecting the control flow of a program. The change can cause issues on some CFI-enabled setups and reports have included Intel Alder Lake-powered machines failing to resume from hibernation.

Zijlstra said the Microsoft engineer "has been working on patches to clean all this up again, but given the current state of things, this stuff just isn't ready. Disable for now, let's try again next cycle."

The offending source is still present, but won't be included in the upcoming stable kernel build.

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