[PATCH 2/4] iommu/amd: Use pci_ats_supported()

Jean-Philippe Brucker
2020-05-15T10:49:03Z

The pci_ats_supported() function checks if a device supports ATS and is
allowed to use it. In addition to checking that the device has an ATS
capability and that the global pci=noats is not set
(pci_ats_disabled()), it also checks if a device is untrusted.

A device is untrusted if it is plugged into an external-facing port such
as Thunderbolt and could be spoofing an existing device to exploit
weaknesses in the IOMMU configuration. By calling pci_ats_supported() we
keep DTE[I]=0 for untrusted devices and abort transactions with
Pretranslated Addresses.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
---
drivers/iommu/amd_iommu.c | 12 ++++--------
1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 1dc3718560d0e8..8b7a9e811d33a6 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -313,16 +313,15 @@ static struct iommu_group *acpihid_device_group(struct device *dev)
static bool pci_iommuv2_capable(struct pci_dev *pdev)
{
static const int caps[] = {
- PCI_EXT_CAP_ID_ATS,
PCI_EXT_CAP_ID_PRI,
PCI_EXT_CAP_ID_PASID,
};
int i, pos;

- if (pci_ats_disabled())
+ if (!pci_ats_supported(pdev))
return false;

- for (i = 0; i < 3; ++i) {
+ for (i = 0; i < 2; ++i) {
pos = pci_find_ext_capability(pdev, caps[i]);
if (pos == 0)
return false;
@@ -3150,11 +3149,8 @@ int amd_iommu_device_info(struct pci_dev *pdev,

memset(info, 0, sizeof(*info));

- if (!pci_ats_disabled()) {
- pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_ATS);
- if (pos)
- info->flags |= AMD_IOMMU_DEVICE_FLAG_ATS_SUP;
- }
+ if (pci_ats_supported(pdev))
+ info->flags |= AMD_IOMMU_DEVICE_FLAG_ATS_SUP;

pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
if (pos)
--
2.26.2