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
