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iommu/vt-d: Force IOMMU on for platform opt in hint

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Intel VT-d spec added a new DMA_CTRL_PLATFORM_OPT_IN_FLAG flag in DMAR
ACPI table [1] for BIOS to report compliance about platform initiated
DMA restricted to RMRR ranges when transferring control to the OS. 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 OS also treats this as a hint that the
IOMMU should be enabled to prevent DMA attacks from possible malicious
devices.

A use of this flag is Kernel DMA protection for Thunderbolt [2] which in
practice means that IOMMU should be enabled for PCIe devices connected
to the Thunderbolt ports. With IOMMU enabled for these devices, all DMA
operations are limited in the range reserved for it, thus the DMA
attacks are prevented. All these devices are enumerated in the PCI/PCIe
module and marked with an untrusted flag.

This forces IOMMU to be enabled if DMA_CTRL_PLATFORM_OPT_IN_FLAG is set
in DMAR ACPI table and there are PCIe devices marked as untrusted in the
system. This can be turned off by adding "intel_iommu=off" in the kernel
command line, if any problems are found.

[1] https://software.intel.com/sites/default/files/managed/c5/15/vt-directed-io-spec.pdf
[2] https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt

Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Reviewed-by: Joerg Roedel <jroedel@suse.de>
Acked-by: Joerg Roedel <jroedel@suse.de>
This commit is contained in:
Lu Baolu 2018-10-23 15:45:01 +08:00 • committed by Mika Westerberg
parent 617654aae5
commit 89a6079df7
3 changed files with 84 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

8
include/linux/dmar.h
View file

@ -39,6 +39,7 @@ struct acpi_dmar_header;
/* DMAR Flags */
#define DMAR_INTR_REMAP 0x1
#define DMAR_X2APIC_OPT_OUT 0x2
#define DMAR_PLATFORM_OPT_IN 0x4
struct intel_iommu;
@ -170,6 +171,8 @@ static inline int dmar_ir_hotplug(struct dmar_drhd_unit *dmaru, bool insert)
{ return 0; }
#endif /* CONFIG_IRQ_REMAP */
extern bool dmar_platform_optin(void);
#else /* CONFIG_DMAR_TABLE */
static inline int dmar_device_add(void *handle)
@ -182,6 +185,11 @@ static inline int dmar_device_remove(void *handle)
return 0;
}
static inline bool dmar_platform_optin(void)
{
return false;
}
#endif /* CONFIG_DMAR_TABLE */
struct irte {