Messages in this thread | | | Date | Tue, 8 Jun 2021 22:06:18 +0200 | From | Borislav Petkov <> | Subject | Re: [patch V3 4/6] x86/pkru: Make PKRU=0 actually work |
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On Tue, Jun 08, 2021 at 09:15:42PM +0200, Thomas Gleixner wrote: > But if nothing touched the FPU between T1 scheduling out and back in, > then the fpregs_state is still valid which means switch_fpu_return() > does nothing and just clears TIF_NEED_FPU_LOAD. Back to user space with > DEFAULT_PKRU loaded. -> FAIL #2!
Ah ok.
> Why? It was clearly wrong and I can reproduce it with a hack which > forces a schedule to a kernel thread and it fails all the way back to > user space.
Oh, I was speculating about some weird luserspace's behavior of clearing PKRU and then relying on the buggy behavior of getting PKRU restored to DEFAULT_PKRU.
I know, it is nuts but it is user-visible change. And yeah, probably nothing does that...
> I chased that because I observed sporadic failures when forcing PKRU to > init state and then observed the default key being written. I had some > extra trace_printks there to analyze something completely different :)
As you do. :-)
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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