On 2/16/22 02:05, Greg KH wrote: >>> How was this tested, and what do the maintainers of this subsystem >>> think? And will you be around to fix the bugs in this when they are >>> found? >> This has been trivial to reproduce, I've used a small repro which I've >> put here: https://gist.github.com/bgaff/9f8cbfc8dd22e60f9492e4f0aff8f04f >> , I also was able to reproduce this using the protection_keys self >> tests on a 11th Gen Core i5-1135G7. I'm happy to commit to addressing >> any bugs that may appear. I'll see what the maintainers say, but there >> is also a smaller fix that just involves using this_cpu_read() in >> switch_fpu_finish() for this specific issue, although that approach >> isn't as clean. > Can you add the test to the in-kernel tests so that we make sure it is > fixed and never comes back? It would be great if Brian could confirm this. But, I'm 99% sure that this can be reproduced in the vm/protection_keys.c selftest, if you run it for long enough. The symptom here is corruption of the PKRU register. I created *lots* of bugs like this during protection keys development so the selftest keeps a shadow copy of the register to specifically watch for corruption. It's _plausible_ that no one ever ran the pkey selftests with a clang-compiled kernel for long enough to hit this issue.
