[PATCH v5 1/2] PCI: ACPI: Support Microsoft's "DmaProperty"

[PATCH v5 1/2] PCI: ACPI: Support Microsoft's "DmaProperty"

[Rajat Jain]

The "DmaProperty" is supported and documented by Microsoft here:
https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports
They use this property for DMA protection:
https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt

Support the "DmaProperty" with the same semantics. This is useful for
internal PCI devices that do not hang off a PCIe rootport, but offer
an attack surface for DMA attacks (e.g. internal network devices).

Signed-off-by: Rajat Jain <rajatja@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
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  | 16 ++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
index d0986bda2964..20603cacc28d 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 1f15ab7eabf8..378e05096c52 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -1350,12 +1350,28 @@ static void pci_acpi_set_external_facing(struct pci_dev *dev)
 		dev->external_facing = 1;
 }
 
+static void pci_acpi_check_for_dma_protection(struct pci_dev *dev)
+{
+	u8 val;
+
+	/*
+	 * Property also used by Microsoft Windows for same purpose,
+	 * (to implement DMA protection from a device, using the IOMMU).
+	 */
+	if (device_property_read_u8(&dev->dev, "DmaProperty", &val))
+		return;
+
+	if (val)
+		dev->untrusted = 1;
+}
+
 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_acpi_check_for_dma_protection(pci_dev);
 	pci_acpi_add_edr_notifier(pci_dev);
 
 	pci_acpi_add_pm_notifier(adev, pci_dev);
-- 
2.35.1.1021.g381101b075-goog

[PATCH v5 2/2] PCI: Rename pci_dev->untrusted to pci_dev->untrusted_dma

[Rajat Jain]

Rename the field to make it more clear, that the device can execute DMA
attacks on the system, and thus the system may need protection from
such attacks from this device.

No functional change intended.

Signed-off-by: Rajat Jain <rajatja@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
v5: Use "untrusted_dma" as property name, based on feedback.
    Reorder the patches in the series.
v4: Initial version, created based on comments on other patch

 drivers/iommu/dma-iommu.c   | 6 +++---
 drivers/iommu/intel/iommu.c | 2 +-
 drivers/iommu/iommu.c       | 2 +-
 drivers/pci/ats.c           | 2 +-
 drivers/pci/pci-acpi.c      | 2 +-
 drivers/pci/pci.c           | 2 +-
 drivers/pci/probe.c         | 8 ++++----
 drivers/pci/quirks.c        | 2 +-
 include/linux/pci.h         | 5 +++--
 9 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index d85d54f2b549..7cbe300fe907 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -497,14 +497,14 @@ static int iova_reserve_iommu_regions(struct device *dev,
 	return ret;
 }
 
-static bool dev_is_untrusted(struct device *dev)
+static bool dev_has_untrusted_dma(struct device *dev)
 {
-	return dev_is_pci(dev) && to_pci_dev(dev)->untrusted;
+	return dev_is_pci(dev) && to_pci_dev(dev)->untrusted_dma;
 }
 
 static bool dev_use_swiotlb(struct device *dev)
 {
-	return IS_ENABLED(CONFIG_SWIOTLB) && dev_is_untrusted(dev);
+	return IS_ENABLED(CONFIG_SWIOTLB) && dev_has_untrusted_dma(dev);
 }
 
 /**
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 92fea3fbbb11..9246b7c9ab46 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -5570,7 +5570,7 @@ intel_iommu_enable_nesting(struct iommu_domain *domain)
  */
 static bool risky_device(struct pci_dev *pdev)
 {
-	if (pdev->untrusted) {
+	if (pdev->untrusted_dma) {
 		pci_info(pdev,
 			 "Skipping IOMMU quirk for dev [%04X:%04X] on untrusted PCI link\n",
 			 pdev->vendor, pdev->device);
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 8b86406b7162..79fb66af2e68 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1522,7 +1522,7 @@ static int iommu_get_def_domain_type(struct device *dev)
 {
 	const struct iommu_ops *ops = dev->bus->iommu_ops;
 
-	if (dev_is_pci(dev) && to_pci_dev(dev)->untrusted)
+	if (dev_is_pci(dev) && to_pci_dev(dev)->untrusted_dma)
 		return IOMMU_DOMAIN_DMA;
 
 	if (ops->def_domain_type)
diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
index c967ad6e2626..477c16ba9341 100644
--- a/drivers/pci/ats.c
+++ b/drivers/pci/ats.c
@@ -42,7 +42,7 @@ bool pci_ats_supported(struct pci_dev *dev)
 	if (!dev->ats_cap)
 		return false;
 
-	return (dev->untrusted == 0);
+	return (dev->untrusted_dma == 0);
 }
 EXPORT_SYMBOL_GPL(pci_ats_supported);
 
diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index 378e05096c52..1d5a284c3661 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -1362,7 +1362,7 @@ static void pci_acpi_check_for_dma_protection(struct pci_dev *dev)
 		return;
 
 	if (val)
-		dev->untrusted = 1;
+		dev->untrusted_dma = 1;
 }
 
 void pci_acpi_setup(struct device *dev, struct acpi_device *adev)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 9ecce435fb3f..1fb0eb8646c8 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -958,7 +958,7 @@ static void pci_std_enable_acs(struct pci_dev *dev)
 	ctrl |= (cap & PCI_ACS_UF);
 
 	/* Enable Translation Blocking for external devices and noats */
-	if (pci_ats_disabled() || dev->external_facing || dev->untrusted)
+	if (pci_ats_disabled() || dev->external_facing || dev->untrusted_dma)
 		ctrl |= (cap & PCI_ACS_TB);
 
 	pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 17a969942d37..d2a9b26fcede 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1587,7 +1587,7 @@ static void set_pcie_thunderbolt(struct pci_dev *dev)
 		dev->is_thunderbolt = 1;
 }
 
-static void set_pcie_untrusted(struct pci_dev *dev)
+static void pci_set_untrusted_dma(struct pci_dev *dev)
 {
 	struct pci_dev *parent;
 
@@ -1596,8 +1596,8 @@ static void set_pcie_untrusted(struct pci_dev *dev)
 	 * untrusted as well.
 	 */
 	parent = pci_upstream_bridge(dev);
-	if (parent && (parent->untrusted || parent->external_facing))
-		dev->untrusted = true;
+	if (parent && (parent->untrusted_dma || parent->external_facing))
+		dev->untrusted_dma = true;
 }
 
 static void pci_set_removable(struct pci_dev *dev)
@@ -1862,7 +1862,7 @@ int pci_setup_device(struct pci_dev *dev)
 	/* Need to have dev->cfg_size ready */
 	set_pcie_thunderbolt(dev);
 
-	set_pcie_untrusted(dev);
+	pci_set_untrusted_dma(dev);
 
 	/* "Unknown power state" */
 	dev->current_state = PCI_UNKNOWN;
diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index 5f46fed01e6c..7ca3c2cdfb20 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -5134,7 +5134,7 @@ static int pci_quirk_enable_intel_spt_pch_acs(struct pci_dev *dev)
 	ctrl |= (cap & PCI_ACS_CR);
 	ctrl |= (cap & PCI_ACS_UF);
 
-	if (pci_ats_disabled() || dev->external_facing || dev->untrusted)
+	if (pci_ats_disabled() || dev->external_facing || dev->untrusted_dma)
 		ctrl |= (cap & PCI_ACS_TB);
 
 	pci_write_config_dword(dev, pos + INTEL_SPT_ACS_CTRL, ctrl);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 678fecdf6b81..b7c5fede0b93 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -444,13 +444,14 @@ struct pci_dev {
 	unsigned int	shpc_managed:1;		/* SHPC owned by shpchp */
 	unsigned int	is_thunderbolt:1;	/* Thunderbolt controller */
 	/*
-	 * Devices marked being untrusted are the ones that can potentially
+	 * Devices marked with untrusted_dma are the ones that can potentially
 	 * execute DMA attacks and similar. They are typically connected
 	 * through external ports such as Thunderbolt but not limited to
 	 * that. When an IOMMU is enabled they should be getting full
 	 * mappings to make sure they cannot access arbitrary memory.
 	 */
-	unsigned int	untrusted:1;
+	unsigned int	untrusted_dma:1;
+
 	/*
 	 * Info from the platform, e.g., ACPI or device tree, may mark a
 	 * device as "external-facing".  An external-facing device is
-- 
2.35.1.1021.g381101b075-goog

Re: [PATCH v5 1/2] PCI: ACPI: Support Microsoft's "DmaProperty"

[Rafael J. Wysocki]

On Fri, Mar 25, 2022 at 7:46 PM Rajat Jain <rajatja@google.com> wrote:
>
> The "DmaProperty" is supported and documented by Microsoft here:
> https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports
> They use this property for DMA protection:
> https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt
>
> Support the "DmaProperty" with the same semantics. This is useful for
> internal PCI devices that do not hang off a PCIe rootport, but offer
> an attack surface for DMA attacks (e.g. internal network devices).
>
> Signed-off-by: Rajat Jain <rajatja@google.com>
> Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
> 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  | 16 ++++++++++++++++
>  2 files changed, 19 insertions(+)
>
> diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
> index d0986bda2964..20603cacc28d 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 1f15ab7eabf8..378e05096c52 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -1350,12 +1350,28 @@ static void pci_acpi_set_external_facing(struct pci_dev *dev)
>                 dev->external_facing = 1;
>  }
>
> +static void pci_acpi_check_for_dma_protection(struct pci_dev *dev)
> +{
> +       u8 val;
> +
> +       /*
> +        * Property also used by Microsoft Windows for same purpose,
> +        * (to implement DMA protection from a device, using the IOMMU).
> +        */
> +       if (device_property_read_u8(&dev->dev, "DmaProperty", &val))
> +               return;
> +
> +       if (val)
> +               dev->untrusted = 1;
> +}
> +
>  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_acpi_check_for_dma_protection(pci_dev);
>         pci_acpi_add_edr_notifier(pci_dev);
>
>         pci_acpi_add_pm_notifier(adev, pci_dev);
> --
> 2.35.1.1021.g381101b075-goog
>

Re: [PATCH v5 2/2] PCI: Rename pci_dev->untrusted to pci_dev->untrusted_dma

[Rafael J. Wysocki]

On Fri, Mar 25, 2022 at 7:46 PM Rajat Jain <rajatja@google.com> wrote:
>
> Rename the field to make it more clear, that the device can execute DMA
> attacks on the system, and thus the system may need protection from
> such attacks from this device.
>
> No functional change intended.
>
> Signed-off-by: Rajat Jain <rajatja@google.com>
> Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
> v5: Use "untrusted_dma" as property name, based on feedback.
>     Reorder the patches in the series.
> v4: Initial version, created based on comments on other patch
>
>  drivers/iommu/dma-iommu.c   | 6 +++---
>  drivers/iommu/intel/iommu.c | 2 +-
>  drivers/iommu/iommu.c       | 2 +-
>  drivers/pci/ats.c           | 2 +-
>  drivers/pci/pci-acpi.c      | 2 +-
>  drivers/pci/pci.c           | 2 +-
>  drivers/pci/probe.c         | 8 ++++----
>  drivers/pci/quirks.c        | 2 +-
>  include/linux/pci.h         | 5 +++--
>  9 files changed, 16 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index d85d54f2b549..7cbe300fe907 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -497,14 +497,14 @@ static int iova_reserve_iommu_regions(struct device *dev,
>         return ret;
>  }
>
> -static bool dev_is_untrusted(struct device *dev)
> +static bool dev_has_untrusted_dma(struct device *dev)
>  {
> -       return dev_is_pci(dev) && to_pci_dev(dev)->untrusted;
> +       return dev_is_pci(dev) && to_pci_dev(dev)->untrusted_dma;
>  }
>
>  static bool dev_use_swiotlb(struct device *dev)
>  {
> -       return IS_ENABLED(CONFIG_SWIOTLB) && dev_is_untrusted(dev);
> +       return IS_ENABLED(CONFIG_SWIOTLB) && dev_has_untrusted_dma(dev);
>  }
>
>  /**
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 92fea3fbbb11..9246b7c9ab46 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -5570,7 +5570,7 @@ intel_iommu_enable_nesting(struct iommu_domain *domain)
>   */
>  static bool risky_device(struct pci_dev *pdev)
>  {
> -       if (pdev->untrusted) {
> +       if (pdev->untrusted_dma) {
>                 pci_info(pdev,
>                          "Skipping IOMMU quirk for dev [%04X:%04X] on untrusted PCI link\n",
>                          pdev->vendor, pdev->device);
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 8b86406b7162..79fb66af2e68 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1522,7 +1522,7 @@ static int iommu_get_def_domain_type(struct device *dev)
>  {
>         const struct iommu_ops *ops = dev->bus->iommu_ops;
>
> -       if (dev_is_pci(dev) && to_pci_dev(dev)->untrusted)
> +       if (dev_is_pci(dev) && to_pci_dev(dev)->untrusted_dma)
>                 return IOMMU_DOMAIN_DMA;
>
>         if (ops->def_domain_type)
> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> index c967ad6e2626..477c16ba9341 100644
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -42,7 +42,7 @@ bool pci_ats_supported(struct pci_dev *dev)
>         if (!dev->ats_cap)
>                 return false;
>
> -       return (dev->untrusted == 0);
> +       return (dev->untrusted_dma == 0);
>  }
>  EXPORT_SYMBOL_GPL(pci_ats_supported);
>
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index 378e05096c52..1d5a284c3661 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -1362,7 +1362,7 @@ static void pci_acpi_check_for_dma_protection(struct pci_dev *dev)
>                 return;
>
>         if (val)
> -               dev->untrusted = 1;
> +               dev->untrusted_dma = 1;
>  }
>
>  void pci_acpi_setup(struct device *dev, struct acpi_device *adev)
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 9ecce435fb3f..1fb0eb8646c8 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -958,7 +958,7 @@ static void pci_std_enable_acs(struct pci_dev *dev)
>         ctrl |= (cap & PCI_ACS_UF);
>
>         /* Enable Translation Blocking for external devices and noats */
> -       if (pci_ats_disabled() || dev->external_facing || dev->untrusted)
> +       if (pci_ats_disabled() || dev->external_facing || dev->untrusted_dma)
>                 ctrl |= (cap & PCI_ACS_TB);
>
>         pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 17a969942d37..d2a9b26fcede 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1587,7 +1587,7 @@ static void set_pcie_thunderbolt(struct pci_dev *dev)
>                 dev->is_thunderbolt = 1;
>  }
>
> -static void set_pcie_untrusted(struct pci_dev *dev)
> +static void pci_set_untrusted_dma(struct pci_dev *dev)
>  {
>         struct pci_dev *parent;
>
> @@ -1596,8 +1596,8 @@ static void set_pcie_untrusted(struct pci_dev *dev)
>          * untrusted as well.
>          */
>         parent = pci_upstream_bridge(dev);
> -       if (parent && (parent->untrusted || parent->external_facing))
> -               dev->untrusted = true;
> +       if (parent && (parent->untrusted_dma || parent->external_facing))
> +               dev->untrusted_dma = true;
>  }
>
>  static void pci_set_removable(struct pci_dev *dev)
> @@ -1862,7 +1862,7 @@ int pci_setup_device(struct pci_dev *dev)
>         /* Need to have dev->cfg_size ready */
>         set_pcie_thunderbolt(dev);
>
> -       set_pcie_untrusted(dev);
> +       pci_set_untrusted_dma(dev);
>
>         /* "Unknown power state" */
>         dev->current_state = PCI_UNKNOWN;
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 5f46fed01e6c..7ca3c2cdfb20 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -5134,7 +5134,7 @@ static int pci_quirk_enable_intel_spt_pch_acs(struct pci_dev *dev)
>         ctrl |= (cap & PCI_ACS_CR);
>         ctrl |= (cap & PCI_ACS_UF);
>
> -       if (pci_ats_disabled() || dev->external_facing || dev->untrusted)
> +       if (pci_ats_disabled() || dev->external_facing || dev->untrusted_dma)
>                 ctrl |= (cap & PCI_ACS_TB);
>
>         pci_write_config_dword(dev, pos + INTEL_SPT_ACS_CTRL, ctrl);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 678fecdf6b81..b7c5fede0b93 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -444,13 +444,14 @@ struct pci_dev {
>         unsigned int    shpc_managed:1;         /* SHPC owned by shpchp */
>         unsigned int    is_thunderbolt:1;       /* Thunderbolt controller */
>         /*
> -        * Devices marked being untrusted are the ones that can potentially
> +        * Devices marked with untrusted_dma are the ones that can potentially
>          * execute DMA attacks and similar. They are typically connected
>          * through external ports such as Thunderbolt but not limited to
>          * that. When an IOMMU is enabled they should be getting full
>          * mappings to make sure they cannot access arbitrary memory.
>          */
> -       unsigned int    untrusted:1;
> +       unsigned int    untrusted_dma:1;
> +
>         /*
>          * Info from the platform, e.g., ACPI or device tree, may mark a
>          * device as "external-facing".  An external-facing device is
> --
> 2.35.1.1021.g381101b075-goog
>

Re: [PATCH v5 1/2] PCI: ACPI: Support Microsoft's "DmaProperty"

[Bjorn Helgaas]

In subject,

  PCI/ACPI: ...

would be consistent with previous history (at least things coming
through the PCI tree :)).

On Fri, Mar 25, 2022 at 11:46:08AM -0700, Rajat Jain wrote:
> The "DmaProperty" is supported and documented by Microsoft here:
> https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports

Here's a more specific link (could probably be referenced below to
avoid cluttering the text here):

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

> They use this property for DMA protection:
> https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt
> 
> Support the "DmaProperty" with the same semantics. This is useful for
> internal PCI devices that do not hang off a PCIe rootport, but offer
> an attack surface for DMA attacks (e.g. internal network devices).

Same semantics as what?

The MS description of "ExternalFacingPort" says:

  This ACPI object enables the operating system to identify externally
  exposed PCIe hierarchies, such as Thunderbolt.

and "DmaProperty" says:

  This ACPI object enables the operating system to identify internal
  PCIe hierarchies that are easily accessible by users (such as,
  Laptop M.2 PCIe slots accessible by way of a latch) and require
  protection by the OS Kernel DMA Protection mechanism.

I don't really understand why they called out "laptop M.2 PCIe slots"
here.  Is the idea that those are more accessible than a standard
internal PCIe slot?  Seems like a pretty small distinction to me.

I can understand your example of internal network devices adding an
attack surface.  But I don't see how "DmaProperty" helps identify
those.  Wouldn't a NIC in a standard internal PCIe slot add the same
attack surface?

> Signed-off-by: Rajat Jain <rajatja@google.com>
> Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
> 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  | 16 ++++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
> index d0986bda2964..20603cacc28d 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 1f15ab7eabf8..378e05096c52 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -1350,12 +1350,28 @@ static void pci_acpi_set_external_facing(struct pci_dev *dev)
>  		dev->external_facing = 1;
>  }
>  
> +static void pci_acpi_check_for_dma_protection(struct pci_dev *dev)

I try to avoid function names like *_check_*() because they don't give
any hint about whether there's a side effect or what direction things
are going.  I prefer things that return a value or make sense when
used as a predicate.  Maybe something like this?

  int pci_dev_has_dma_property(struct pci_dev *dev)

  dev->untrusted |= pci_dev_has_dma_property(pci_dev);

> +{
> +	u8 val;
> +
> +	/*
> +	 * Property also used by Microsoft Windows for same purpose,
> +	 * (to implement DMA protection from a device, using the IOMMU).
> +	 */
> +	if (device_property_read_u8(&dev->dev, "DmaProperty", &val))

The MS web page says a _DSD with this property must be implemented in
the Root Port device scope, but we don't enforce that here.  We *do*
enforce it in pci_acpi_set_untrusted().  Shouldn't we do the same
here?

We currently look at three properties from the same _DSD:

  DmaProperty
  ExternalFacingPort
  HotPlugSupportInD3

For "HotPlugSupportInD3", we check that "value == 1".  For
"ExternalFacingPort", we check that it's non-zero.  The MS doc isn't
explicit about the values, but shows "1" in the sample ASL.  I think
we should handle all three cases the same.

The first two use device_property_read_u8(); the last uses
acpi_dev_get_property().  Again, I think they should all be the same.

acpi_dev_get_property() is easier for me to read because there are
slightly fewer layers of abstraction between _DSD and
acpi_dev_get_property().

But IIUC, device_property_read_u8() works for either ACPI or DT
properties, and maybe there is interest in using this for DT systems.
None of these appear in any in-tree DTs, but maybe it is important to
handle these in DTs?

If that's the case, this code would no longer be specific to ACPI and
should be moved to somewhere that's compiled even when CONFIG_ACPI
isn't set.

> +		return;
> +
> +	if (val)
> +		dev->untrusted = 1;
> +}
> +
>  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_acpi_check_for_dma_protection(pci_dev);
>  	pci_acpi_add_edr_notifier(pci_dev);
>  
>  	pci_acpi_add_pm_notifier(adev, pci_dev);
> -- 
> 2.35.1.1021.g381101b075-goog
> 

Re: [PATCH v5 1/2] PCI: ACPI: Support Microsoft's "DmaProperty"

[Rajat Jain]

Hello Bjorn,


On Thu, Apr 7, 2022 at 12:17 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> In subject,
>
>   PCI/ACPI: ...
>
> would be consistent with previous history (at least things coming
> through the PCI tree :)).

Will do.

>
> On Fri, Mar 25, 2022 at 11:46:08AM -0700, Rajat Jain wrote:
> > The "DmaProperty" is supported and documented by Microsoft here:
> > https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports
>
> Here's a more specific link (could probably be referenced below to
> avoid cluttering the text here):
>
> 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

Will do.

>
> > They use this property for DMA protection:
> > https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt
> >
> > Support the "DmaProperty" with the same semantics. This is useful for
> > internal PCI devices that do not hang off a PCIe rootport, but offer
> > an attack surface for DMA attacks (e.g. internal network devices).
>
> Same semantics as what?

Er, I meant the same semantics as the "DmaProperty". Please also see below.

>
> The MS description of "ExternalFacingPort" says:
>
>   This ACPI object enables the operating system to identify externally
>   exposed PCIe hierarchies, such as Thunderbolt.
>

No, my patch doesn't have to do with this one.

> and "DmaProperty" says:
>
>   This ACPI object enables the operating system to identify internal
>   PCIe hierarchies that are easily accessible by users (such as,
>   Laptop M.2 PCIe slots accessible by way of a latch) and require
>   protection by the OS Kernel DMA Protection mechanism.

Yes, this is the property that my patch uses. Microsoft has agreed to
update this documentation (in a sideband thread that I also copied you
on), with the updated semantics that this property can be used to
identify any PCI devices that require Kernel DMA protection. i.e. the
property is not restricted to identify "internal PCIe hierarchies"
(starting at root port), but to "any PCI device".

>
> I don't really understand why they called out "laptop M.2 PCIe slots"
> here.  Is the idea that those are more accessible than a standard
> internal PCIe slot?  Seems like a pretty small distinction to me.
>
> I can understand your example of internal network devices adding an
> attack surface.  But I don't see how "DmaProperty" helps identify
> those.  Wouldn't a NIC in a standard internal PCIe slot add the same
> attack surface?

Yes it would. The attack surface is the same. They probably only
thought of devices external to the SoC (starting from a root port)
when designing this property and thus called out internal M.2 PCI
slots. But nowhave realized that this could be opened to any PCI
device.

>
> > Signed-off-by: Rajat Jain <rajatja@google.com>
> > Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> > ---
> > 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  | 16 ++++++++++++++++
> >  2 files changed, 19 insertions(+)
> >
> > diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
> > index d0986bda2964..20603cacc28d 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 1f15ab7eabf8..378e05096c52 100644
> > --- a/drivers/pci/pci-acpi.c
> > +++ b/drivers/pci/pci-acpi.c
> > @@ -1350,12 +1350,28 @@ static void pci_acpi_set_external_facing(struct pci_dev *dev)
> >               dev->external_facing = 1;
> >  }
> >
> > +static void pci_acpi_check_for_dma_protection(struct pci_dev *dev)
>
> I try to avoid function names like *_check_*() because they don't give
> any hint about whether there's a side effect or what direction things
> are going.  I prefer things that return a value or make sense when
> used as a predicate.  Maybe something like this?
>
>   int pci_dev_has_dma_property(struct pci_dev *dev)
>
>   dev->untrusted |= pci_dev_has_dma_property(pci_dev);
>

OK, will do.


> > +{
> > +     u8 val;
> > +
> > +     /*
> > +      * Property also used by Microsoft Windows for same purpose,
> > +      * (to implement DMA protection from a device, using the IOMMU).
> > +      */
> > +     if (device_property_read_u8(&dev->dev, "DmaProperty", &val))
>
> The MS web page says a _DSD with this property must be implemented in
> the Root Port device scope, but we don't enforce that here.  We *do*
> enforce it in pci_acpi_set_untrusted().  Shouldn't we do the same
> here?

No, the whole point of doing this (please refer to the discussion on
the previous versions of this patch) was that we want to have a
property that is NOT limited to the root ports only. And we have
reached an agreement with Microsoft about that.

>
> We currently look at three properties from the same _DSD:
>
>   DmaProperty
>   ExternalFacingPort
>   HotPlugSupportInD3
>
> For "HotPlugSupportInD3", we check that "value == 1".  For
> "ExternalFacingPort", we check that it's non-zero.  The MS doc isn't
> explicit about the values, but shows "1" in the sample ASL.  I think
> we should handle all three cases the same.

I think we can handle all three cases with "value==1". I will send a
separate patch for the ExternalFacingPort, and will fixup this patch
too).

>
> The first two use device_property_read_u8(); the last uses
> acpi_dev_get_property().  Again, I think they should all be the same.
>
> acpi_dev_get_property() is easier for me to read because there are
> slightly fewer layers of abstraction between _DSD and
> acpi_dev_get_property().

I'd prefer that too, and can change it to acpi_dev_get_property.

>
> But IIUC, device_property_read_u8() works for either ACPI or DT
> properties, and maybe there is interest in using this for DT systems.
> None of these appear in any in-tree DTs, but maybe it is important to
> handle these in DTs?
>
> If that's the case, this code would no longer be specific to ACPI and
> should be moved to somewhere that's compiled even when CONFIG_ACPI
> isn't set.

I think unifying ACPI and GPIO systems to use the same code / function
to read the properties might be more work/investigation, because
reading the properties for ACPI system happens much later than DT
systems (For acpi systems, it happens in pci_acpi_setup() which is
called much later). Given that no one wants to use this for DT
systems, I'd prefer for this to be ACPI specific for now, and then we
can solve it for DT once someone needs it.

WDYT?

Thanks & Best regards,

Rajat

>
> > +             return;
> > +
> > +     if (val)
> > +             dev->untrusted = 1;
> > +}
> > +
> >  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_acpi_check_for_dma_protection(pci_dev);
> >       pci_acpi_add_edr_notifier(pci_dev);
> >
> >       pci_acpi_add_pm_notifier(adev, pci_dev);
> > --
> > 2.35.1.1021.g381101b075-goog
> >

Re: [PATCH v5 1/2] PCI: ACPI: Support Microsoft's "DmaProperty"

[Bjorn Helgaas]

On Thu, Apr 14, 2022 at 04:15:47PM -0700, Rajat Jain via iommu wrote:
> On Thu, Apr 7, 2022 at 12:17 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > On Fri, Mar 25, 2022 at 11:46:08AM -0700, Rajat Jain wrote:

> > > Support the "DmaProperty" with the same semantics. This is useful for
> > > internal PCI devices that do not hang off a PCIe rootport, but offer
> > > an attack surface for DMA attacks (e.g. internal network devices).
> >
> > Same semantics as what?
> 
> Er, I meant the same semantics as the "DmaProperty". Please also see below.

"Support the 'DmaProperty' with the same semantics as 'DmaProperty'"
doesn't help much, so there must be a little more to the story :)

> > The MS description of "ExternalFacingPort" says:
> >
> >   This ACPI object enables the operating system to identify externally
> >   exposed PCIe hierarchies, such as Thunderbolt.
> 
> No, my patch doesn't have to do with this one.

I know, but it's similar, and I'm just hoping we can deal with them
consistently.

> > and "DmaProperty" says:
> >
> >   This ACPI object enables the operating system to identify internal
> >   PCIe hierarchies that are easily accessible by users (such as,
> >   Laptop M.2 PCIe slots accessible by way of a latch) and require
> >   protection by the OS Kernel DMA Protection mechanism.
> 
> Yes, this is the property that my patch uses. Microsoft has agreed to
> update this documentation (in a sideband thread that I also copied you
> on), with the updated semantics that this property can be used to
> identify any PCI devices that require Kernel DMA protection. i.e. the
> property is not restricted to identify "internal PCIe hierarchies"
> (starting at root port), but to "any PCI device".
> 
> > I don't really understand why they called out "laptop M.2 PCIe slots"
> > here.  Is the idea that those are more accessible than a standard
> > internal PCIe slot?  Seems like a pretty small distinction to me.
> >
> > I can understand your example of internal network devices adding an
> > attack surface.  But I don't see how "DmaProperty" helps identify
> > those.  Wouldn't a NIC in a standard internal PCIe slot add the same
> > attack surface?
> 
> Yes it would. The attack surface is the same. They probably only
> thought of devices external to the SoC (starting from a root port)
> when designing this property and thus called out internal M.2 PCI
> slots. But nowhave realized that this could be opened to any PCI
> device.

> > > +      * Property also used by Microsoft Windows for same purpose,
> > > +      * (to implement DMA protection from a device, using the IOMMU).
> > > +      */
> > > +     if (device_property_read_u8(&dev->dev, "DmaProperty", &val))
> >
> > The MS web page says a _DSD with this property must be implemented in
> > the Root Port device scope, but we don't enforce that here.  We *do*
> > enforce it in pci_acpi_set_untrusted().  Shouldn't we do the same
> > here?
> 
> No, the whole point of doing this (please refer to the discussion on
> the previous versions of this patch) was that we want to have a
> property that is NOT limited to the root ports only. And we have
> reached an agreement with Microsoft about that.

We need to either mention the fact that we're going beyond what the MS
web page says or (ideally, as you are doing) get the page updated with
the semantics you need.

> > But IIUC, device_property_read_u8() works for either ACPI or DT
> > properties, and maybe there is interest in using this for DT systems.
> > None of these appear in any in-tree DTs, but maybe it is important to
> > handle these in DTs?
> >
> > If that's the case, this code would no longer be specific to ACPI and
> > should be moved to somewhere that's compiled even when CONFIG_ACPI
> > isn't set.
> 
> I think unifying ACPI and GPIO systems to use the same code / function
> to read the properties might be more work/investigation, because
> reading the properties for ACPI system happens much later than DT
> systems (For acpi systems, it happens in pci_acpi_setup() which is
> called much later). Given that no one wants to use this for DT
> systems, I'd prefer for this to be ACPI specific for now, and then we
> can solve it for DT once someone needs it.

I think it's OK to make it ACPI-specific for now.

Bjorn