Re: [PATCH 00/11 v3] x86: load FPU registers on return to userland

[Andy Lutomirski]

> On Oct 4, 2018, at 9:45 AM, Rik van Riel <riel@xxxxxxxxxxx> wrote:
> 
> On Thu, 2018-10-04 at 16:05 +0200, Sebastian Andrzej Siewior wrote:
> 
> 
>> In v3 I dropped that decouple idea. I also learned that the wrpkru
>> instruction is not privileged and so caching it in kernel does not
>> work.
> 
> Wait, so any thread can bypass its memory protection
> keys, even if there is a seccomp filter preventing
> it from calling the PKRU syscalls?
> 
> Is that intended?
> 
> Is that simply a hardware limitation, or something
> where we can set a flag somewhere to force tasks to
> go through the kernel?
> 
> 

Hardware limitation.