linux-kernel - Re: Avoid speculative indirect calls in kernel

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Message-ID: <CA+55aFzCocoK+4kxAUEhaxxba4RTv3ewBmhiZ8Osc9iDkBtCEQ@mail.gmail.com>
Date:   Wed, 3 Jan 2018 15:51:35 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     tglx@...uxtronix.de,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        dwmw@...zon.co.uk, Tim Chen <tim.c.chen@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: Avoid speculative indirect calls in kernel

On Wed, Jan 3, 2018 at 3:09 PM, Andi Kleen <andi@...stfloor.org> wrote:
> This is a fix for Variant 2 in
> https://googleprojectzero.blogspot.com/2018/01/reading-privileged-memory-with-side.html
>
> Any speculative indirect calls in the kernel can be tricked
> to execute any kernel code, which may allow side channel
> attacks that can leak arbitrary kernel data.

Why is this all done without any configuration options?

A *competent* CPU engineer would fix this by making sure speculation
doesn't happen across protection domains. Maybe even a L1 I$ that is
keyed by CPL.

I think somebody inside of Intel needs to really take a long hard look
at their CPU's, and actually admit that they have issues instead of
writing PR blurbs that say that everything works as designed.

.. and that really means that all these mitigation patches should be
written with "not all CPU's are crap" in mind.

Or is Intel basically saying "we are committed to selling you shit
forever and ever, and never fixing anything"?

Because if that's the case, maybe we should start looking towards the
ARM64 people more.

Please talk to management. Because I really see exactly two possibibilities:

 - Intel never intends to fix anything

OR

 - these workarounds should have a way to disable them.

Which of the two is it?

                   Linus