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

[Kees Cook]

On Thu, Feb 21, 2019 at 9:33 AM Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> 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