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

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Pavel Machek <pavel@denx.de>
Cc: Jesse Barnes <jsbarnes@google.com>,
	Rajat Jain <rajatja@google.com>,
	Rajat Jain <rajatxjain@gmail.com>,
	Bjorn Helgaas <helgaas@kernel.org>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	"Krishnakumar,
	Lalithambika" <lalithambika.krishnakumar@intel.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	linux-pci <linux-pci@vger.kernel.org>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Prashant Malani <pmalani@google.com>,
	Benson Leung <bleung@google.com>, Todd Broch <tbroch@google.com>,
	Alex Levin <levinale@google.com>,
	Mattias Nissler <mnissler@google.com>,
	Zubin Mithra <zsm@google.com>,
	Bernie Keany <bernie.keany@intel.com>,
	Aaron Durbin <adurbin@google.com>,
	Diego Rivas <diegorivas@google.com>,
	Duncan Laurie <dlaurie@google.com>,
	Furquan Shaikh <furquan@google.com>,
	Christian Kellner <christian@kellner.me>,
	Alex Williamson <alex.williamson@redhat.com>,
	Joerg Roedel <joro@8bytes.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] Restrict the untrusted devices, to bind to only a set of "whitelisted" drivers
Date: Wed, 1 Jul 2020 12:57:14 +0200	[thread overview]
Message-ID: <20200701105714.GA2098169@kroah.com> (raw)
In-Reply-To: <20200701084750.GA7144@amd>

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