Date:   Mon, 8 Jun 2020 10:03:38 -0700
From:   Jesse Barnes <jsbarnes@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     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

> > I feel a lot of resistance to the proposal, however, I'm not hearing
> > any realistic solutions that may help us to move forward. We want to
> > go with a solution that is acceptable upstream as that is our mission,
> > and also helps the community, however the behemoth task of "inspect
> > all drivers and fix them" before launching a product is really an
> > unfair ask I feel :-(. Can you help us by suggesting a proposal that
> > does not require us to trust a driver equally for internal / external
> > devices?
>
> I have no idea why you feel you have to "inspect all drivers" other than
> the fact that for some reason _you_ do not feel they are secure today.
>
> What type of "assurance" are you, or anyone else going to be able to
> provide for any kernel driver that would meet such a "I feel good now"
> level?  Have you done that work for any specific driver already so that
> you can show us what you mean by this effort?  Perhaps it's as simple as
> "oh look, this tool over here runs 'clean' on the source code, all is
> good!", or not, I really have no idea.

I think there's a disconnect somewhere in this discussion... maybe
we're just approaching this with different assumptions?

I think you recognize the potential for driver vulnerabilities when
binding to new or potentially hostile devices that may be spoofing
DID/VID/class/etc than then go on to abuse driver trust or the driver
using unvalidated inputs from the device to crash or run arbitrary
code on the target system.

Yes such drivers should be fixed, no doubt.  But without lots of
fuzzing (we're working on this) and testing we'd like to avoid
exposing that attack surface at all.

I think your suggestion to disable driver binding once the initial
bus/slot devices have been bound will probably work for this
situation.  I just wanted to be clear that without some auditing,
fuzzing, and additional testing, we simply have to assume that drivers
are *not* secure and avoid using them on untrusted devices until we're
fairly confident they can handle them (whether just misbehaving or
malicious), in combination with other approaches like IOMMUs of
course.  And this isn't because we don't trust driver authors or
kernel developers to dtrt, it's just that for many devices (maybe USB
is an exception) I think driver authors haven't had to consider this
case much, and so I think it's prudent to expect bugs in this area
that we need to find & fix.

Thanks,
Jesse

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