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

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Date:   Thu, 04 Oct 2018 12:45:08 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 00/11 v3] x86: load FPU registers on return to userland

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?

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