[PATCH v3 10/10] iommu/vt-d: Disallow nesting on domains with read-only mappings

Yi Liu
2023-05-11T14:53:23Z

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.

Disallow the nested translation when there are read-only pages in the
corresponding second-stage mappings. And, no read-only pages are allowed
to be configured in the second-stage table of a nested translation.
For the latter, an alternative is to disallow read-only mappings in
any stage-2 domain as long as it's ever been used as a parent. In this
way, we can simply replace the user counter with a flag.

In concept if the user understands this errata and does expect to
enable nested translation it should never install any RO mapping
in stage-2 in the entire VM life cycle."

Reference from Sapphire Rapids Specification Update [1], errata details,
SPR17.

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

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
---
drivers/iommu/intel/iommu.c | 13 +++++++++++++
drivers/iommu/intel/iommu.h | 4 ++++
drivers/iommu/intel/nested.c | 22 ++++++++++++++++++++--
include/uapi/linux/iommufd.h | 12 +++++++++++-
4 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 20d4ae1cb8a6..42288bd449a0 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2150,6 +2150,7 @@ __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
struct dma_pte *first_pte = NULL, *pte = NULL;
unsigned int largepage_lvl = 0;
unsigned long lvl_pages = 0;
+ unsigned long flags;
phys_addr_t pteval;
u64 attr;

@@ -2159,6 +2160,17 @@ __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->read_only_mapped) {
+ spin_lock_irqsave(&domain->lock, flags);
+ if (domain->nested_users > 0) {
+ spin_unlock_irqrestore(&domain->lock, flags);
+ return -EINVAL;
+ }
+
+ domain->read_only_mapped = true;
+ spin_unlock_irqrestore(&domain->lock, flags);
+ }
+
attr = prot & (DMA_PTE_READ | DMA_PTE_WRITE | DMA_PTE_SNP);
attr |= DMA_FL_PTE_PRESENT;
if (domain->use_first_level) {
@@ -4756,6 +4768,7 @@ static void *intel_iommu_hw_info(struct device *dev, u32 *length)
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/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
index 581596d90c1b..95644c6815af 100644
--- a/drivers/iommu/intel/iommu.h
+++ b/drivers/iommu/intel/iommu.h
@@ -616,6 +616,10 @@ struct dmar_domain {
int agaw;
/* maximum mapped address */
u64 max_addr;
+ /* domain has mappings with read-only permission */
+ bool read_only_mapped;
+ /* user nested domain count */
+ int nested_users;
};

/* Nested user domain */
diff --git a/drivers/iommu/intel/nested.c b/drivers/iommu/intel/nested.c
index d13fbcd3f5a6..9092ce28382c 100644
--- a/drivers/iommu/intel/nested.c
+++ b/drivers/iommu/intel/nested.c
@@ -61,7 +61,14 @@ static int intel_nested_attach_dev(struct iommu_domain *domain,

static void intel_nested_domain_free(struct iommu_domain *domain)
{
- kfree(to_dmar_domain(domain));
+ struct dmar_domain *dmar_domain = to_dmar_domain(domain);
+ struct dmar_domain *s2_domain = dmar_domain->s2_domain;
+ unsigned long flags;
+
+ spin_lock_irqsave(&s2_domain->lock, flags);
+ s2_domain->nested_users--;
+ spin_unlock_irqrestore(&s2_domain->lock, flags);
+ kfree(dmar_domain);
}

static void intel_nested_invalidate(struct device *dev,
@@ -143,14 +150,25 @@ struct iommu_domain *intel_nested_domain_alloc(struct iommu_domain *s2_domain,
const union iommu_domain_user_data *user_data)
{
const struct iommu_hwpt_intel_vtd *vtd = (struct iommu_hwpt_intel_vtd *)user_data;
+ struct dmar_domain *s2_dmar_domain = to_dmar_domain(s2_domain);
struct dmar_domain *domain;
+ unsigned long flags;

domain = kzalloc(sizeof(*domain), GFP_KERNEL_ACCOUNT);
if (!domain)
return NULL;

+ spin_lock_irqsave(&s2_dmar_domain->lock, flags);
+ if (s2_dmar_domain->read_only_mapped) {
+ spin_unlock_irqrestore(&s2_dmar_domain->lock, flags);
+ kfree(domain);
+ return NULL;
+ }
+ s2_dmar_domain->nested_users++;
+ spin_unlock_irqrestore(&s2_dmar_domain->lock, flags);
+
domain->use_first_level = true;
- domain->s2_domain = to_dmar_domain(s2_domain);
+ domain->s2_domain = s2_dmar_domain;
domain->s1_pgtbl = vtd->pgtbl_addr;
domain->s1_cfg = *vtd;
domain->domain.ops = &intel_nested_domain_ops;
diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
index b46270a4cf46..8626f36e0353 100644
--- a/include/uapi/linux/iommufd.h
+++ b/include/uapi/linux/iommufd.h
@@ -471,10 +471,20 @@ enum iommu_hw_info_type {
IOMMU_HW_INFO_TYPE_INTEL_VTD,
};

+/**
+ * enum iommu_hw_info_vtd_flags - Flags for VT-d hw_info
+ * @IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17: If set, disallow nesting on domains
+ * with read-only mapping.
+ * 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