On Thu, May 13, 2021 at 10:42 AM Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, May 13, 2021 at 09:39:58AM -0700, Rajat Jain wrote: > > Hello, > > > > On Thu, May 13, 2021 at 6:58 AM Greg Kroah-Hartman > > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Wed, May 12, 2021 at 02:34:57PM -0700, Rajat Jain wrote: > > > > A PCI device is "external_facing" if it's a Root Port with the ACPI > > > > "ExternalFacingPort" property or if it has the DT "external-facing" > > > > property. We consider everything downstream from such a device to > > > > be removable by user. > > > > > > > > We're mainly concerned with consumer platforms with user accessible > > > > thunderbolt ports that are vulnerable to DMA attacks, and we expect those > > > > ports to be identified as "ExternalFacingPort". Devices in traditional > > > > hotplug slots can technically be removed, but the expectation is that > > > > unless the port is marked with "ExternalFacingPort", such devices are less > > > > accessible to user / may not be removed by end user, and thus not exposed > > > > as "removable" to userspace. > > > > > > > > Set pci_dev_type.supports_removable so the device core exposes the > > > > "removable" file in sysfs, and tell the device core about removable > > > > devices. > > > > > > > > This can be used by userspace to implment any policies it wants to, > > > > tailored specifically for user removable devices. Eg usage: > > > > https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2591812 > > > > https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2795038 > > > > (code uses such an attribute to remove external PCI devicces or disable > > > > features on them as needed by the policy desired) > > > > > > > > Signed-off-by: Rajat Jain <rajatja@xxxxxxxxxx> > > > > --- > > > > v3: - commit log updated > > > > - Rename set_pci_dev_removable() -> pci_set_removable() > > > > - Call it after applying early PCI quirks. > > > > v2: Add documentation > > > > > > > > Documentation/ABI/testing/sysfs-devices-removable | 3 ++- > > > > drivers/pci/pci-sysfs.c | 1 + > > > > drivers/pci/probe.c | 12 ++++++++++++ > > > > 3 files changed, 15 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/Documentation/ABI/testing/sysfs-devices-removable b/Documentation/ABI/testing/sysfs-devices-removable > > > > index 9dabcad7cdcd..ec0b243f5db4 100644 > > > > --- a/Documentation/ABI/testing/sysfs-devices-removable > > > > +++ b/Documentation/ABI/testing/sysfs-devices-removable > > > > @@ -14,4 +14,5 @@ Description: > > > > > > > > Currently this is only supported by USB (which infers the > > > > information from a combination of hub descriptor bits and > > > > - platform-specific data such as ACPI). > > > > + platform-specific data such as ACPI) and PCI (which gets this > > > > + from ACPI / device tree). > > > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c > > > > index beb8d1f4fafe..38b3259ba333 100644 > > > > --- a/drivers/pci/pci-sysfs.c > > > > +++ b/drivers/pci/pci-sysfs.c > > > > @@ -1541,4 +1541,5 @@ static const struct attribute_group *pci_dev_attr_groups[] = { > > > > > > > > const struct device_type pci_dev_type = { > > > > .groups = pci_dev_attr_groups, > > > > + .supports_removable = true, > > > > }; > > > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > > > > index 3a62d09b8869..3515afeeaba8 100644 > > > > --- a/drivers/pci/probe.c > > > > +++ b/drivers/pci/probe.c > > > > @@ -1575,6 +1575,16 @@ static void set_pcie_untrusted(struct pci_dev *dev) > > > > dev->untrusted = true; > > > > } > > > > > > > > +static void pci_set_removable(struct pci_dev *dev) > > > > +{ > > > > + struct pci_dev *parent = pci_upstream_bridge(dev); > > > > + if (parent && > > > > + (parent->external_facing || dev_is_removable(&parent->dev))) > > > > + dev_set_removable(&dev->dev, DEVICE_REMOVABLE); > > > > + else > > > > + dev_set_removable(&dev->dev, DEVICE_FIXED); > > > > +} > > > > > > Always run checkpatch.pl so you don't get grumpy maintainers telling you > > > to run checkpatch.pl :( > > > > Yes, I did (it gave me 0 errors and 0 warnings). Please let me know if > > I need to fix something and I'll be happy to fix that. > > > > > > > > And why does external_facing come into play here? I know you say it > > > above, but you should also put it here into the code for when we need to > > > look at it in a few months and wonder what in the world this is doing. > > > > Ack, will do. > > > > > > > > Also, are you SURE this is correct and will handle the hotpluggable PCI > > > devices in things like drawers and the like? > > > > Yes, me and Bjorn discussed this in the v2 of this patch > > (https://patchwork.kernel.org/project/linux-usb/patch/20210424021631.1972022-2-rajatja@xxxxxxxxxx/), > > and yes, this can take care of the hot-pluggable trays if the firmware > > marks the slots external-facing. > > Ok, I'll trust you two :) > > > > What is the goal here in exposing this information to userspace, who is > > > going to use it and what is it going to be used for? > > > > The goal here is to implement policies regarding usage of external PCI > > devices, in userspace. ChromeOS is using it for things like: > > - Remove external PCI devices when a user logs out. > > remove them how? disconnect the device from the system through what > method? echo 1 > /sys/bus/pci/devices/<device>/remove > > > - Don't allow new external PCI devices while the screen is locked. > > Don't allow how? Don't allow the binding of a driver to a device, or > the device to be discovered at all? What controls this? Actually Sorry, this was a wrong recollection. > > > - collect metrics about usage of external PCI devices (how many users > > actually use it etc). > > - disable certain features (that are deemed to be dangerous) for > > external PCI network cards. > > What is a "dangerous" network feature, RDMA? For now, we disable offloading of receive path generic / segmentation / checksum features to the external PCI hardware, based on our security team's recommendations. Thanks, Rajat > > thanks, > > greg k-h
