| Message ID | 20220325184609.4059963-1-rajatja@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v5,1/2] PCI: ACPI: Support Microsoft's "DmaProperty" | expand |
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 >
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 >
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 > >
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
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);