[PATCH v8 8/8] iommu/vt-d: Disallow read-only mappings to nest parent domain

Yi Liu
2023-10-26T04:43:25Z

From: Lu Baolu <baolu.lu@linux.intel.com>

When remapping hardware is configured by system software in scalable mode
as Nested (PGTT=011b) and with PWSNP field Set in the PASID-table-entry,
it may Set Accessed bit and Dirty bit (and Extended Access bit if enabled)
in first-stage page-table entries even when second-stage mappings indicate
that corresponding first-stage page-table is Read-Only.

As the result, contents of pages designated by VMM as Read-Only can be
modified by IOMMU via PML5E (PML4E for 4-level tables) access as part of
address translation process due to DMAs issued by Guest.

This disallows read-only mappings in the domain that is supposed to be used
as nested parent. Reference from Sapphire Rapids Specification Update [1],
errata details, SPR17. Userspace should know this limitation by checking
the IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17 flag reported in the IOMMU_GET_HW_INFO
ioctl.

[1] https://www.intel.com/content/www/us/en/content-details/772415/content-details.html

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
drivers/iommu/intel/iommu.c | 6 ++++++
include/uapi/linux/iommufd.h | 12 +++++++++++-
2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 4ce372d5d4f3..a2c429855cc0 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2194,6 +2194,11 @@ __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
if ((prot & (DMA_PTE_READ|DMA_PTE_WRITE)) == 0)
return -EINVAL;

+ if (!(prot & DMA_PTE_WRITE) && domain->nested_parent) {
+ pr_err_ratelimited("Read-only mapping is disallowed on the domain which serves as the parent in a nested configuration, due to HW errata (ERRATA_772415_SPR17)\n");
+ return -EINVAL;
+ }
+
attr = prot & (DMA_PTE_READ | DMA_PTE_WRITE | DMA_PTE_SNP);
attr |= DMA_FL_PTE_PRESENT;
if (domain->use_first_level) {
@@ -4850,6 +4855,7 @@ static void *intel_iommu_hw_info(struct device *dev, u32 *length, u32 *type)
if (!vtd)
return ERR_PTR(-ENOMEM);

+ vtd->flags = IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17;
vtd->cap_reg = iommu->cap;
vtd->ecap_reg = iommu->ecap;
*length = sizeof(*vtd);
diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
index 3ce5ee5f09b6..0b2bc6252e2c 100644
--- a/include/uapi/linux/iommufd.h
+++ b/include/uapi/linux/iommufd.h
@@ -443,10 +443,20 @@ struct iommu_hwpt_alloc {
};
#define IOMMU_HWPT_ALLOC _IO(IOMMUFD_TYPE, IOMMUFD_CMD_HWPT_ALLOC)

+/**
+ * enum iommu_hw_info_vtd_flags - Flags for VT-d hw_info
+ * @IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17: If set, disallow read-only mappings
+ * on a nested_parent domain.
+ * https://www.intel.com/content/www/us/en/content-details/772415/content-details.html
+ */
+enum iommu_hw_info_vtd_flags {
+ IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17 = 1 << 0,
+};
+
/**
* struct iommu_hw_info_vtd - Intel VT-d hardware information
*
- * @flags: Must be 0
+ * @flags: Combination of enum iommu_hw_info_vtd_flags
* @__reserved: Must be 0
*
* @cap_reg: Value of Intel VT-d capability register defined in VT-d spec
--
2.34.1