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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Rajat Jain <rajatja@google.com>,
	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 09:12:39 +0200
Message-ID: <20200610071239.GC1923109@kroah.com> (raw)
In-Reply-To: <20200609210400.GA1461839@bjorn-Precision-5520>

On Tue, Jun 09, 2020 at 04:04:00PM -0500, Bjorn Helgaas wrote:
> On Sun, Jun 07, 2020 at 01:36:32PM +0200, Greg Kroah-Hartman wrote:
> 
> > Your "problem" I think can be summed up a bit more concise:
> > 	- you don't trust kernel drivers to be "secure" for untrusted
> > 	  devices
> > 	- you only want to bind kernel drivers to "internal" devices
> > 	  automatically as you "trust" drivers in that situation.
> > 	- you want to only bind specific kernel drivers that you somehow
> > 	  feel are "secure" to untrusted devices "outside" of a system
> > 	  when those devices are added to the system.
> > 
> > Is that correct?
> > 
> > If so, fine, you can do that today with the bind/unbind ability of
> > drivers, right?  After boot with your "trusted" drivers bound to
> > "internal" devices, turn off autobind of drivers to devices and then
> > manually bind them when you see new devices show up, as those "must" be
> > from external devices (see the bind/unbind files that all drivers export
> > for how to do this, and old lwn.net articles, this feature has been
> > around for a very long time.)
> > 
> > I know for USB you can do this, odds are PCI you can turn off
> > autobinding as well, as I think this is a per-bus flag somewhere.  If
> > that's not exported to userspace, should be trivial to do so, should be
> > somewere in the driver model already...
> > 
> > Ah, yes, look at the "drivers_autoprobe" and "drivers_probe" files in
> > sysfs for all busses.  Do those not work for you?
> > 
> > My other points are the fact that you don't want to put policy in the
> > kernel, and I think that you can do everything you want in userspace
> > today, except maybe the fact that trying to determine what is "inside"
> > and "outside" is not always easy given that most hardware does not
> > export this information properly, if at all.  Go work with the firmware
> > people on that issue please, that would be most helpful for everyone
> > involved to get that finally straightened out.
> 
> To sketch this out, my understanding of how this would work is:
> 
>   - Expose the PCI pdev->untrusted bit in sysfs.  We don't expose this
>     today, but doing so would be trivial.  I think I would prefer a
>     sysfs name like "external" so it's more descriptive and less of a
>     judgment.
> 
>     This comes from either the DT "external-facing" property or the
>     ACPI "ExternalFacingPort" property.  

Good idea, but as people have pointed out, even these don't always work
so userspace will need to be able to override that somehow :(

>   - All devices present at boot are enumerated.  Any statically built
>     drivers will bind to them before any userspace code runs.
> 
>     If you want to keep statically built drivers from binding, you'd
>     need to invent some mechanism so pci_driver_init() could clear
>     drivers_autoprobe after registering pci_bus_type.
> 
>   - Early userspace code prevents modular drivers from automatically
>     binding to PCI devices:
> 
>       echo 0 > /sys/bus/pci/drivers_autoprobe
> 
>     This prevents modular drivers from binding to all devices, whether
>     present at boot or hot-added.
> 
>   - Userspace code uses the sysfs "bind" file to control which drivers
>     are loaded and can bind to each device, e.g.,
> 
>       echo 0000:02:00.0 > /sys/bus/pci/drivers/nvme/bind

Seems good to me, and also matches what the current USB tools do for
this type of thing.

thanks,

greg k-h

  parent reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-01 23:07 Rajat Jain
2020-05-04 11:47 ` Jean-Philippe Brucker
2020-05-04 11:59   ` Jean-Philippe Brucker
2020-05-04 19:17     ` Rajat Jain
2020-05-05 12:33 ` Mika Westerberg
2020-05-06 18:51   ` Rajat Jain
2020-05-11 20:31 ` Rajat Jain
2020-05-13 15:19 ` Bjorn Helgaas
2020-05-13 21:26   ` Rajat Jain
2020-05-14 13:42     ` Mika Westerberg
2020-05-14 19:12     ` Raj, Ashok
2020-05-15  2:18       ` Rajat Jain
2020-05-26 16:30         ` Rajat Jain
2020-06-01 23:25           ` Bjorn Helgaas
2020-06-02  5:06             ` Greg Kroah-Hartman
2020-06-03  2:27               ` Rajat Jain
2020-06-03  6:07                 ` Greg Kroah-Hartman
2020-06-03 11:51                   ` Rajat Jain
2020-06-03 12:16                     ` Greg Kroah-Hartman
2020-06-03 12:57                       ` Rajat Jain
2020-06-03 13:29                         ` Greg Kroah-Hartman
2020-06-04 19:38                       ` Rajat Jain
2020-06-05  8:02                         ` Greg Kroah-Hartman
2020-06-06  1:08                           ` Rajat Jain
2020-06-07 11:36                             ` Greg Kroah-Hartman
2020-06-08 17:03                               ` Jesse Barnes
2020-06-08 17:50                                 ` Greg Kroah-Hartman
2020-06-08 18:29                                   ` Jesse Barnes
2020-06-08 18:41                                     ` Rajat Jain
2020-06-09  9:54                                       ` Greg Kroah-Hartman
2020-06-30 21:46                                         ` Pavel Machek
2020-06-09  5:57                                     ` Greg Kroah-Hartman
2020-06-30 21:45                                 ` Pavel Machek
2020-07-01  6:54                                   ` Greg Kroah-Hartman
2020-07-01  8:47                                     ` Pavel Machek
2020-07-01 10:57                                       ` Greg Kroah-Hartman
2020-07-01 11:08                                         ` Pavel Machek
2020-06-09 21:04                               ` Bjorn Helgaas
2020-06-09 23:23                                 ` Rajat Jain
2020-06-10  0:04                                   ` Bjorn Helgaas
2020-06-10  0:30                                     ` Rajat Jain
2020-06-10 20:17                                       ` Rajat Jain
2020-06-10 23:09                                         ` Bjorn Helgaas
2020-06-10 23:01                                       ` Bjorn Helgaas
2020-06-10 23:46                                         ` Rajat Jain
2020-06-10  7:13                                   ` Greg Kroah-Hartman
2020-06-10  1:34                                 ` Oliver O'Halloran
2020-06-10 19:57                                   ` Rajat Jain
2020-06-16  1:24                                     ` Rajat Jain
2020-06-10  7:12                                 ` Greg Kroah-Hartman [this message]
2020-05-15 12:44     ` Joerg Roedel

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