linux-kernel - Re: [RFC] Restrict the untrusted devices, to bind to only a set of "whitelisted" drivers

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Date:   Wed, 1 Jul 2020 12:57:14 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     Jesse Barnes <jsbarnes@...gle.com>,
        Rajat Jain <rajatja@...gle.com>,
        Rajat Jain <rajatxjain@...il.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Krishnakumar, Lalithambika" <lalithambika.krishnakumar@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Prashant Malani <pmalani@...gle.com>,
        Benson Leung <bleung@...gle.com>,
        Todd Broch <tbroch@...gle.com>,
        Alex Levin <levinale@...gle.com>,
        Mattias Nissler <mnissler@...gle.com>,
        Zubin Mithra <zsm@...gle.com>,
        Bernie Keany <bernie.keany@...el.com>,
        Aaron Durbin <adurbin@...gle.com>,
        Diego Rivas <diegorivas@...gle.com>,
        Duncan Laurie <dlaurie@...gle.com>,
        Furquan Shaikh <furquan@...gle.com>,
        Christian Kellner <christian@...lner.me>,
        Alex Williamson <alex.williamson@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] Restrict the untrusted devices, to bind to only a set of
 "whitelisted" drivers

On Wed, Jul 01, 2020 at 10:47:50AM +0200, Pavel Machek wrote:
> Hi!
> 
> > > We normally trust the hardware NOT to be malicious. (Because if hacker
> > > has physical access to hardware and lot of resources, you lost).
> > 
> > That is what we originally thought, however the world has changed and we
> > need to be better about this, now that it is trivial to create a "bad"
> > device.
> 
> I'm not disagreeing.
> 
> > > This is still true today, but maybe trusting USB devices is bad idea,
> > > so drivers are being cleaned up. PCI drivers will be WORSE in this
> > > regard. And you can't really protect against malicious CPU, and it is
> > > very very hard to protect against malicous RAM (probably not practical
> > > without explicit CPU support).
> > > 
> > > Linux was designed with "don't let hackers near your hardware" threat
> > > model in mind.
> > 
> > Yes, it originally was designed that way, but again, the world has
> > changed so we have to change with it.  That is why USB has for a long
> > time now, allowed you to not bind drivers to devices that you do not
> > "trust", and that trust can be determined by userspace.  That all came
> > about thanks to the work done by the wireless USB spec people and kernel
> > authors, which showed that maybe you just don't want to trust any device
> > that comes within range of your system :)
> 
> Again, not disagreeing; but note the scale here.
> 
> It is mandatory to defend against malicious wireless USB devices.

Turns out there are no more wireless USB devices in the world, and the
code for that is gone from Linux :)

> We probably should work on robustness against malicious USB devices.

We are, and do have, that support today.

> Malicious PCI-express devices are lot less of concern.

Not really, they are a lot of concern to some people.  Valid attacks are
out there today, see the thunderbolt attacks that numerous people have
done and published recently and for many years.

> Defending against malicious CPU/RAM does not make much sense.

That's what the spectre and rowhammer fixes have been for :)

thanks,

greg k-h