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

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Message-Id: <A6DB636D-0021-48A4-98C5-7F4B3DFC98D2@amacapital.net>
Date:   Thu, 18 Oct 2018 14:58:16 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        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 Oct 18, 2018, at 2:24 PM, Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:
> 
> On 2018-10-18 13:56:24 [-0700], Dave Hansen wrote:
>>> 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.
> 
> Okay, this makes things easier. Let document that for kernel threads we
> use PKRU=0. This should be happening in my try right now. I double check
> tomorrow just in case…
> 
> 

If you document that, please at least document that it’s a bug and not intended behavior.