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

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Date:   Sun, 7 Jan 2018 23:10:38 +0100
From:   Willy Tarreau <w@....eu>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jon Masters <jcm@...hat.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andi Kleen <andi@...stfloor.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jeff Law <law@...hat.com>, Nick Clifton <nickc@...hat.com>
Subject: Re: Avoid speculative indirect calls in kernel

On Sun, Jan 07, 2018 at 07:55:11PM +0100, Borislav Petkov wrote:
> > Just like you have to trust your plane's pilot eventhough you don't
> > know him personally.
> 
> Funny you should make that analogy. Remember that germanwings pilot?
> People trusted him too.
> 
> Now imagine if the plane had protection against insane pilots... some of
> those people might still be alive, who knows...

Sure but despite this case many people continue to take the plane because
it's their only option to cross half of the world in a reasonable time.

Boris, I'm *not* contesting the performance resulting from the fixes,
and I would never have been able to produce them myself had I to, so
I'm really glad we have them. I just want to be clear that the big drop
some of us are facing is not an option *at all* for certain processes
in certain environments and that we'll either continue to run with
pti=off or with pti=on + a finer grained setting ASAP.

I mean, the kernel is not the only sensitive part in a system (and
sometimes it's even not at all). A kernel + a userland processes
deliver a service, each in it role. Breaking one or the other can be
similar or sometimes the trouble can be worse for one than the other.
But for some situations, the good work condition of the combination of
the two is critical, and even a kernel compromission could be a detail
compared to the impact of something crashing at full load. Sometimes a
userspace compromission would already be critical enough that the risk
is not higher by accepting to take it for the kernel as well.

In my specific case, on LB appliances, I don't really care what happens
once haproxy has already been compromised, it's too late. End of the
game, all sensitive information are already disclosed at this point.
What I'd rather avoid however is the occasional sysop who has an account
on the machine to retrieve some stats once in a while that would suddenly
be able to get more than these stats. That's where I draw the line for
*this* use case. Plenty of others will have plenty of other perception
and that's fine.

Cheers,
Willy