linux-kernel - Re: [PATCH] x86/asm: Pin sensitive CR4 bits

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Message-ID: <CAGXu5jKPtL4oSa_7QJEXVc++idNNH9GA1Y=z3tQrorRTs0fnsA@mail.gmail.com>
Date:   Wed, 20 Feb 2019 09:01:27 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Dominik Brodowski <linux@...inikbrodowski.net>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        X86 ML <x86@...nel.org>
Subject: Re: [PATCH] x86/asm: Pin sensitive CR4 bits

On Wed, Feb 20, 2019 at 12:15 AM Dominik Brodowski
<linux@...inikbrodowski.net> wrote:
>
> On Tue, Feb 19, 2019 at 04:54:49PM -0800, Kees Cook wrote:
> > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> > index cb28e98a0659..7e0ea4470f8e 100644
> > --- a/arch/x86/kernel/cpu/common.c
> > +++ b/arch/x86/kernel/cpu/common.c
> > @@ -312,10 +312,16 @@ static __init int setup_disable_smep(char *arg)
> >  }
> >  __setup("nosmep", setup_disable_smep);
> >
> > +volatile unsigned long cr4_pin __ro_after_init;
> > +EXPORT_SYMBOL_GPL(cr4_pin);
>
> Where is this export needed?

I use it in lkdtm (which I was going to land through the drivers tree,
but I haven't sent to Greg):

https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=kspp/x86/cr4

-- 
Kees Cook