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

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Date:   Thu, 4 Jan 2018 23:11:58 -0500
From:   Jon Masters <jcm@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "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>,
        Dave Hansen <dave.hansen@...el.com>, Jeff Law <law@...hat.com>,
        Nick Clifton <nickc@...hat.com>
Subject: Re: Avoid speculative indirect calls in kernel

On 01/04/2018 07:54 PM, Thomas Gleixner wrote:
> On Thu, 4 Jan 2018, Jon Masters wrote:
>> P.S. I've an internal document where I've been tracking "nice to haves"
>> for later, and one of them is whether it makes sense to tag binaries as
>> "trusted" (e.g. extended attribute, label, whatever). It was something I
>> wanted to bring up at some point as potentially worth considering.
> 
> Scratch that. There is no such thing as a trusted binary.

I agree with your sentiment, but for those mitigations that carry a
significant performance overhead (for example IBRS at the moment, and on
some other architectures where we might not end up with retpolines)
there /could/ be some value in leaving them on by default but allowing a
sysadmin to decide to trust a given application/container and accept the
risk. Sure, it's selectively weakened security, I get that. I am not
necessarily advocating this, just suggesting it be discussed.

[ I also totally get that you can extend variant 2 to have any
application that interacts with another abuse it (even over a pipe or a
socket, etc. provided they share the same cache and take untrusted data
that can lead to some kind of load within a speculation window), and
there are a ton of ways to still cause an attack in that case. ]

Jon.

-- 
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