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

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Message-ID: <CALCETrX7Bw_VU-muN60qnECZP7Qes9E0Sv5WbSjrni=RG07uZA@mail.gmail.com>
Date:   Mon, 27 Nov 2017 21:23:18 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        michael.schwarz@...k.tugraz.at, moritz.lipp@...k.tugraz.at,
        richard.fellner@...dent.tugraz.at
Subject: Re: [PATCH 2/5] x86/mm/kaiser: Add a banner

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