linux-kernel - Re: [PATCH 05/11] x86/fpu: set PKRU state for kernel threads

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Message-ID: <aedef390-2fb1-8c09-3a69-53d3fd0505da@linux.intel.com>
Date:   Thu, 18 Oct 2018 13:56:24 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Andy Lutomirski <luto@...capital.net>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Andrew Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH 05/11] x86/fpu: set PKRU state for kernel threads

On 10/18/2018 01:46 PM, Andy Lutomirski wrote:
> Setting it to allow-all/none would let the operation always fail or
> succeed which might be an improvement in terms of debugging. However it
> is hard to judge what the correct behaviour should be. Should fail or
> succeed.

Succeed. :)

> But this is not the only loophole: There is ptrace interface which is
> used by gdb (just checked) and also bypasses PKRU. So…

Bypassing protection keys is not a big deal IMNHO.  In places where a
sane one is not readily available, I'm totally fine with just
effectively disabling it (PKRU=0) for the length of time it isn't available.