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

[Andy Lutomirski <luto@kernel.org>]

On Mon, Nov 27, 2017 at 9:03 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> 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@infradead.org> wrote:
>> > So we can more easily see if the shiny got enabled.
>> >
>> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>> > ---
>> >  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?

We need to completely eliminate anything that maps normal kernel
addresses into the usermode tables.

>
> --
> Josh

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