On Tue, Apr 26, 2022 at 4:15 AM Robin Murphy <robin.murphy@xxxxxxx> wrote: > > On 2022-04-26 01:06, Rajat Jain via iommu wrote: > > The "DmaProperty" is supported and currently documented and used by > > Microsoft [link 1 below], to flag internal PCIe root ports that need > > DMA protection [link 2 below]. We have discussed with them and reached > > a common understanding that they shall change their MSDN documentation > > to say that the same property can be used to protect any PCI device, > > and not just internal PCIe root ports (since there is no point > > introducing yet another property for arbitrary PCI devices). This helps > > with security from internal devices that offer an attack surface for > > DMA attacks (e.g. internal network devices). > > > > Support DmaProperty to mark DMA from a PCI device as untrusted. > > > > Link: [1] https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports#identifying-internal-pcie-ports-accessible-to-users-and-requiring-dma-protection > > Link: [2] https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt > > Signed-off-by: Rajat Jain <rajatja@xxxxxxxxxx> > > Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> > > Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > --- > > v6: * Take care of Bjorn's comments: > > - Update the commit log > > - Rename to pci_dev_has_dma_property() > > - Use acpi_dev_get_property() > > v5: * Reorder the patches in the series > > v4: * Add the GUID. > > * Update the comment and commitlog. > > v3: * Use Microsoft's documented property "DmaProperty" > > * Resctrict to ACPI only > > > > drivers/acpi/property.c | 3 +++ > > drivers/pci/pci-acpi.c | 21 +++++++++++++++++++++ > > 2 files changed, 24 insertions(+) > > > > diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c > > index 12bbfe833609..bafe35c301ac 100644 > > --- a/drivers/acpi/property.c > > +++ b/drivers/acpi/property.c > > @@ -48,6 +48,9 @@ static const guid_t prp_guids[] = { > > /* Storage device needs D3 GUID: 5025030f-842f-4ab4-a561-99a5189762d0 */ > > GUID_INIT(0x5025030f, 0x842f, 0x4ab4, > > 0xa5, 0x61, 0x99, 0xa5, 0x18, 0x97, 0x62, 0xd0), > > + /* DmaProperty for PCI devices GUID: 70d24161-6dd5-4c9e-8070-705531292865 */ > > + GUID_INIT(0x70d24161, 0x6dd5, 0x4c9e, > > + 0x80, 0x70, 0x70, 0x55, 0x31, 0x29, 0x28, 0x65), > > }; > > > > /* ACPI _DSD data subnodes GUID: dbb8e3e6-5886-4ba6-8795-1319f52a966b */ > > diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c > > index 3ae435beaf0a..d7c6ba48486f 100644 > > --- a/drivers/pci/pci-acpi.c > > +++ b/drivers/pci/pci-acpi.c > > @@ -1369,12 +1369,33 @@ static void pci_acpi_set_external_facing(struct pci_dev *dev) > > dev->external_facing = 1; > > } > > > > +static int pci_dev_has_dma_property(struct pci_dev *dev) > > +{ > > + struct acpi_device *adev; > > + const union acpi_object *obj; > > + > > + adev = ACPI_COMPANION(&dev->dev); > > + if (!adev) > > + return 0; > > + > > + /* > > + * Property also used by Microsoft Windows for same purpose, > > + * (to implement DMA protection from a device, using the IOMMU). > > Nit: there is no context for "same purpose" here, so this comment is > more confusing than helpful. Might I suggest a rewording like: > > /* > * Property used by Microsoft Windows to enforce IOMMU DMA > * protection for any device that the system might not fully > * trust; we'll honour it the same way. > */ > > ? Sure, will do. > > Personally I think it would have been more logical to handle this in > pci_set_dma_untrusted(), but I see some of those implementation aspects > have already been discussed, and Bjorn's preference definitely wins over > mine here :) Yes, this was discussed. The primary reason is that ACPI properties for PCI devices are not available at the time pci_set_untrusted_dma() is called. Thanks & Best Regards, Rajat > > Thanks, > Robin. > > > + */ > > + if (!acpi_dev_get_property(adev, "DmaProperty", ACPI_TYPE_INTEGER, > > + &obj) && obj->integer.value == 1) > > + return 1; > > + > > + return 0; > > +} > > + > > void pci_acpi_setup(struct device *dev, struct acpi_device *adev) > > { > > struct pci_dev *pci_dev = to_pci_dev(dev); > > > > pci_acpi_optimize_delay(pci_dev, adev->handle); > > pci_acpi_set_external_facing(pci_dev); > > + pci_dev->untrusted |= pci_dev_has_dma_property(pci_dev); > pci_acpi_add_edr_notifier(pci_dev); > > > > pci_acpi_add_pm_notifier(adev, pci_dev);
