[PATCH 2/2] iommu: Use the user PGD for SVA if PTI is enabled

[Jacob Pan]

With page table isolation, the kernel manages two sets of page tables
for each process: one for user one for kernel. When enabling SVA, the
current x86 IOMMU drivers bind device and PASID with the kernel copy
of the process page table.

While there is no known "Meltdown" type of DMA attack, exposing
kernel mapping to DMA intended for userspace makes the system vulnerable
unnecessarily. It also breaks the intention of PTI.

This patch replaces kernel page table PGD with the user counterpart,
thus fulfill the promise of PTI on the DMA side.

Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
---
 drivers/iommu/amd/iommu_v2.c | 4 +++-
 drivers/iommu/intel/svm.c    | 5 ++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/amd/iommu_v2.c b/drivers/iommu/amd/iommu_v2.c
index 696d5555be57..aea3075b94af 100644
--- a/drivers/iommu/amd/iommu_v2.c
+++ b/drivers/iommu/amd/iommu_v2.c
@@ -600,6 +600,7 @@ int amd_iommu_bind_pasid(struct pci_dev *pdev, u32 pasid,
 	struct pasid_state *pasid_state;
 	struct device_state *dev_state;
 	struct mm_struct *mm;
+	pgd_t *pgd;
 	u32 sbdf;
 	int ret;
 
@@ -645,8 +646,9 @@ int amd_iommu_bind_pasid(struct pci_dev *pdev, u32 pasid,
 	if (ret)
 		goto out_unregister;
 
+	pgd = static_cpu_has(X86_FEATURE_PTI) ? kernel_to_user_pgdp(mm->pgd) : mm->pgd;
 	ret = amd_iommu_domain_set_gcr3(dev_state->domain, pasid,
-					__pa(pasid_state->mm->pgd));
+					__pa(pgd));
 	if (ret)
 		goto out_clear_state;
 
diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index 8bcfb93dda56..7472cd98d3e8 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -332,6 +332,7 @@ static struct iommu_sva *intel_svm_bind_mm(struct intel_iommu *iommu,
 	struct intel_svm *svm;
 	unsigned long sflags;
 	int ret = 0;
+	pgd_t *pgd;
 
 	svm = pasid_private_find(mm->pasid);
 	if (!svm) {
@@ -394,7 +395,9 @@ static struct iommu_sva *intel_svm_bind_mm(struct intel_iommu *iommu,
 	sflags = (flags & SVM_FLAG_SUPERVISOR_MODE) ?
 			PASID_FLAG_SUPERVISOR_MODE : 0;
 	sflags |= cpu_feature_enabled(X86_FEATURE_LA57) ? PASID_FLAG_FL5LP : 0;
-	ret = intel_pasid_setup_first_level(iommu, dev, mm->pgd, mm->pasid,
+
+	pgd = static_cpu_has(X86_FEATURE_PTI) ? kernel_to_user_pgdp(mm->pgd) : mm->pgd;
+	ret = intel_pasid_setup_first_level(iommu, dev, pgd, mm->pasid,
 					    FLPT_DEFAULT_DID, sflags);
 	if (ret)
 		goto free_sdev;
-- 
2.25.1