Re: [PATCH 2/5] x86/mm/kaiser: Add a banner

[Josh Poimboeuf]

On Mon, Nov 27, 2017 at 07:36:40PM -0800, Andy Lutomirski wrote:
> On Mon, Nov 27, 2017 at 2:31 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > So we can more easily see if the shiny got enabled.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > ---
> >  arch/x86/mm/kaiser.c |    2 ++
> >  1 file changed, 2 insertions(+)
> >
> > --- a/arch/x86/mm/kaiser.c
> > +++ b/arch/x86/mm/kaiser.c
> > @@ -425,6 +425,8 @@ void __init kaiser_init(void)
> >         if (!kaiser_enabled)
> >                 return;
> >
> > +       printk("All your KAISER are belong to us\n");
> > +
> 
> All your incomprehensible academic names are belong to us.
> 
> On a serious note, can we please banish the name KAISER from all the
> user-facing bits?  No one should be setting a boot option that has a
> name based on an academic project called "Kernel Address Isolation to
> have Side-channels Efficiently Removed".  We're not efficiently
> removing side channels.  The side channels are still very much there.
> Heck, the series as currently presented doesn't even rescue kASLR.  It
> could*, if we were to finish the work that I mostly started and
> completely banish all the normal kernel mappings from the shadow**
> tables.  We're rather inefficiently (and partially!) mitigating the
> fact that certain CPU designers have had their heads up their
> collective arses for *years* and have failed to pay attention to
> numerous academic papers documenting that fact.
> 
> Let's call the user facing bits "separate user pagetables".  If we
> want to make it conditioned on a future cpu cap called
> X86_BUG_REALLY_DUMB_SIDE_CHANNELS, great, assuming a better CPU ever
> shows up.  But please let's not make users look up WTF "KAISER" means.
> 
> * No one ever documented the %*!& side channels AFAIK, so everything
> we're talking about here is mostly speculation.
> 
> ** The word "shadow" needs to die, too.  I know what shadow page
> tables are, and they have *nothing* to do with KAISER.

+1.  Somebody please rename KAISER and shadow page tables for more
clarity.

To fix KASLR I think we need to move (at least parts of) .entry.text,
.irqentry.text, and .entry_trampoline into their own fixed section(s).
Is there anything else missing?

-- 
Josh