Recent systems with Thunderbolt ports may be utilizing IOMMU to prevent DMA attacks. This is different from the previous security level based scheme because the connected device cannot access system memory outside of the regions allocated for it by the driver. When enabled the BIOS makes sure no device can do DMA outside of RMRR (Reserved Memory Region Record) regions. This means that during OS boot, before it enables IOMMU, none of the connected devices can bypass DMA protection for instance by overwriting the data structures used by the IOMMU. The BIOS communicates support for this to the OS by setting a new bit in ACPI DMAR table [1]. Because these systems utilize an IOMMU to block possible DMA attacks, typically (but not always) the Thunderbolt security level is set to "none" which means that all PCIe devices are immediately usable. This also means that Linux needs to follow Windows 10 and enable IOMMU automatically when running on such system otherwise connected devices can read/write system memory pretty much without any restrictions. Since there is a way to identify PCIe root ports that are "external facing" we can put all internal devices to pass through (identity mapping) mode and only external devices need to go through full IOMMU mappings. We add a new flag "untrusted" that is supposed to cover various PCIe devices that may be used to conduct DMA attacks. We also make sure PCIe ATS (Address Translation Service) is not enabled for devices flagged as untrusted because it could be used to bypass IOMMU completely as explained in the changelog of patch 3/4. Finally we expose this information to userspace so tools such as bolt can do more accurate decision whether or not authorize the connected device. [1] https://software.intel.com/sites/default/files/managed/c5/15/vt-directed-io-spec.pdf Previous version of the patch series can be found here: v2: https://lkml.org/lkml/2018/11/26/638 v1: https://www.spinics.net/lists/linux-pci/msg77751.html Changes from v2: * Rename the flag to "untrusted" * Simplify setting the flag for root ports * Dropped loop in set_pcie_untrusted() * Add comment on top of prp_guids explaining the possible caveat resulting when the new GUIDs are treated as equivalent * Updated changelogs according to feedback Changes from v1: * Reword Documentation/admin-guide/thunderbolt.rst to make the feature time frame/platform oriented as there will be systems shipping with Linux installed by default. * Rename the flag is_external to is_untrusted so that we could use the same flag to cover all kinds of "untrusted" PCI devices, not just Thunderbolt connected devices. I still parse the _DSD in PCI/ACPI core because that's where we currently handle "HotPlugSupportInD3" as well. Also updated comments in patch [1/4]. * Added tags from Ashok, Joerg and Yehezkel. I'm assuming they still apply because I did not change the code with the exception of few comments and rename of the flag. Let me know if that's not the case anymore. Lu Baolu (1): iommu/vt-d: Force IOMMU on for platform opt in hint Mika Westerberg (3): PCI / ACPI: Identify untrusted PCI devices iommu/vt-d: Do not enable ATS for untrusted devices thunderbolt: Export IOMMU based DMA protection support to userspace .../ABI/testing/sysfs-bus-thunderbolt | 9 +++ Documentation/admin-guide/thunderbolt.rst | 20 +++++++ drivers/acpi/property.c | 11 ++++ drivers/iommu/dmar.c | 25 +++++++++ drivers/iommu/intel-iommu.c | 56 ++++++++++++++++++- drivers/pci/pci-acpi.c | 19 +++++++ drivers/pci/probe.c | 15 +++++ drivers/thunderbolt/domain.c | 17 ++++++ include/linux/dmar.h | 8 +++ include/linux/pci.h | 8 +++ 10 files changed, 185 insertions(+), 3 deletions(-) -- 2.19.2
