linux-kernel - Re: [PATCH v2] x86/asm: Pin sensitive CR4 bits

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Message-ID: <CAGXu5j+rfR4T2Mo75bfp7L9RAPWQ7xchQTfW3JpDbHRMOocjbQ@mail.gmail.com>
Date:   Thu, 21 Feb 2019 09:37:52 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Jann Horn <jannh@...gle.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        X86 ML <x86@...nel.org>
Subject: Re: [PATCH v2] x86/asm: Pin sensitive CR4 bits

On Thu, Feb 21, 2019 at 9:33 AM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
> On Wed, Feb 20, 2019 at 10:09:34AM -0800, Kees Cook wrote:
> > +     if (WARN_ONCE((val & cr4_pin) != cr4_pin, "cr4 bypass attempt?!\n"))
>
> Printing what bits diverged would be helpful in the unlikely event that the
> WARN_ONCE triggers.  "cr4 bypass attempt" is probably only meaningful to
> people that are already familiar with the code, e.g.:
>
>         if (WARN_ONCE((val & cr4_pin) != cr4_pin,
>             "Attempt to unpin cr4 bits: %lx, cr4 bypass attack?!", ~val & cr4_pin))

Ah yeah, I like it. I'll send a v3. Thanks!

-- 
Kees Cook