A Microsoft change to the Linux kernel caused major breakage, but was caught in time

A change to the Linux 6.13 kernel contributed by a Microsoft engineer ended up changing Linux x86_64 code without proper authorization and in turn causing troubles for users and now set to be disabled ahead of the Linux 6.13 stable release expected next Sunday.
↫ Michael Larabel

What I like about this story is that it seems to underline that the processes, checks, and balances in place in Linux kernel development seem to be working – at least, this time. A breaking change was caught during the prerelease phase, and a fix has been merged to make sure this issue will be fixed before the stable version of Linux 6.13 is released to the wider public. This all sounds great, but there is an element of this story that raises some serious questions.

The change itself was related to EXECMEM_ROX, and was intended to improve performance of 64bit AMD and Intel processors, but in turn, this new code broke Control Flow Integrity on some setups, causing some devices not to wake from hibernation while also breaking other features. What makes this spicy is that the code was merged without acknowledgement from any of the x86 kernel maintainers, which made a lot of people very unhappy – and understandably so.

So while the processes and checks and balances worked here, something still went horribly wrong, as such changes should not be able to be merged without acknowledgement from maintainers. This now makes me wonder how many more times this has happened without causing any instantly discoverable issues. For now, some code has been added to revert the offending changes, and Linux 6.13 will ship with Microsoft’s bad code disabled.