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

From: Bjorn Helgaas <helgaas@kernel.org>
To: Rajat Jain <rajatja@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Rajat Jain <rajatxjain@gmail.com>,
	"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>,
	Jesse Barnes <jsbarnes@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, 10 Jun 2020 18:01:19 -0500	[thread overview]
Message-ID: <20200610230119.GA1528268@bjorn-Precision-5520> (raw)
In-Reply-To: <CACK8Z6G3ycsXxuNiihOXiwwAum8=5aOFOshhFa7cEF__+c-v1A@mail.gmail.com>

On Tue, Jun 09, 2020 at 05:30:13PM -0700, Rajat Jain wrote:
> On Tue, Jun 9, 2020 at 5:04 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > On Tue, Jun 09, 2020 at 04:23:54PM -0700, Rajat Jain wrote:
> > > Thanks for sending out the summary, I was about to send it out but got lazy.
> > > ...

> > > The one thing that still needs more thought is how about the
> > > "pcieport" driver that enumerates the PCI bridges. I'm unsure if it
> > > needs to be whitelisted for further enumeration downstream. What do
> > > you think?
> >
> > The pcieport driver is required for AER, PCIe native hotplug, PME,
> > etc., and it cannot be a module, so the whitelist wouldn't apply to
> > it.
> 
> Not that I see the need, but slight clarification needed just to make
> sure I understand it clearly:
> 
> Since pcieport driver is statically compiled in, AER, pciehp, PME, DPC
> etc will always be enabled for devices plugged in during boot. But I
> can still choose to choose to allow or deny for devices added *after
> boot* using the whitelist, right?

Yes, I think so.  However, if pcieport doesn't claim hot-added devices
like a dock, I don't think hotplug of PCI things downstream from the
dock will work, e.g., if there are Thunderbolt switches in a monitor
or something.

> Also, denying pcieport driver for hot-added PCIe bridges only disables
> these pcieport services on those bridges, but device enumeration
> further downstream those bridges is not an issue?

Right.  Devices without pcieport would not be able to report hotplug
events, so we wouldn't notice hot-adds or -removes involving those
devices.