linux-kernel - Re: [RFC GIT PULL] x86 Page Table Isolation (PTI) syscall entry code preparatory patches

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Message-ID: <CA+55aFyY3e1cYcQv=VuduRzHhxUx4diNPWCdfEhwN9+RnwuY2A@mail.gmail.com>
Date:   Sat, 16 Dec 2017 14:57:25 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC GIT PULL] x86 Page Table Isolation (PTI) syscall entry code
 preparatory patches

On Fri, Dec 15, 2017 at 5:58 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> These are the x86-64 low level entry code preparatory patches for the page table
> isolation patches - which are required for PTI, which addresses KASLR and similar
> information leaks.

Ugh.

Ok, I've read through this, and while I like most of it (I do like the
percpu syscall stack), I have this urge to wait until after rc4. With
the suspend/resume issues, we've had a horrible track record for 4.15
rc's so far, I'l like to not pull another low-level x86 change just
before an rc release and potentially make it four for four broken
rc's.

And I absolutely detest how that cherry-pick branch was done. I can
see why, but:

 - now we have those extra cherry-picks that I already have

 - and the merge commit isn't even a no-op!

Dammit, if the point was to have a branch that worked for 4.14, I can
see that. But look at that merge (on the "other side"), and notice how
the end result is *not* identical to the parent.

IOW, that

  9a818d1a3235 Merge branch 'WIP.x86/pti.base' into x86/pti, to pick
up cherry-picked base tree and preparatory patches

was supposed to be a synchronization point, but if you do

    git diff 9a818d1a3235..9a818d1a3235^

it isn't actually synchronized. It's *almost* synchronized, but not
quite. How did those cherry-picks that were already upstream end up
causing *changes* upstream? That's odd.

So there are some technical oddities in there.

I'll read through it tomorrow again.. Maybe I'll change my mind.

               Linus