x86/vtd: Hide superpage support for SandyBridge IOMMUs

Something causes SandyBridge IOMMUs to choke when sharing EPT pagetables, and
an EPT superpage gets shattered.  The root cause is still under investigation,
but the end result is unusable in combination with CVE-2018-12207 protections.

This is part of XSA-304 / CVE-2018-12207

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/drivers/passthrough/vtd/extern.h b/xen/drivers/passthrough/vtd/extern.h
index fb7edfaef9d6503ce96819e659384562845febee..d698b1d50a1c8d47a07c2a54dd604a2e62e68b35 100644 (file)
--- a/xen/drivers/passthrough/vtd/extern.h
+++ b/xen/drivers/passthrough/vtd/extern.h
@@ -96,6 +96,8 @@ void vtd_ops_postamble_quirk(struct iommu* iommu);
 int __must_check me_wifi_quirk(struct domain *domain,
                                u8 bus, u8 devfn, int map);
 void pci_vtd_quirk(const struct pci_dev *);
+void quirk_iommu_caps(struct iommu *iommu);
+
 bool_t platform_supports_intremap(void);
 bool_t platform_supports_x2apic(void);
 

diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index f242e30caf2e5f6f16a9f52a9801f8da747bb007..8712d3b4dc1057ba1ecf92aa15f4ec926f1f056e 100644 (file)
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1211,6 +1211,8 @@ int __init iommu_alloc(struct acpi_drhd_unit *drhd)
     if ( !(iommu->cap + 1) || !(iommu->ecap + 1) )
         return -ENODEV;
 
+    quirk_iommu_caps(iommu);
+
     if ( cap_fault_reg_offset(iommu->cap) +
          cap_num_fault_regs(iommu->cap) * PRIMARY_FAULT_REG_LEN >= PAGE_SIZE ||
          ecap_iotlb_offset(iommu->ecap) >= PAGE_SIZE )

diff --git a/xen/drivers/passthrough/vtd/quirks.c b/xen/drivers/passthrough/vtd/quirks.c
index d6db8626786a6991a1d267d8951a04d36dcf0c87..b02688e3165d62c49ef6df2aa0d13503fe0f53c5 100644 (file)
--- a/xen/drivers/passthrough/vtd/quirks.c
+++ b/xen/drivers/passthrough/vtd/quirks.c
@@ -540,3 +540,28 @@ void pci_vtd_quirk(const struct pci_dev *pdev)
         break;
     }
 }
+
+void __init quirk_iommu_caps(struct iommu *iommu)
+{
+    /*
+     * IOMMU Quirks:
+     *
+     * SandyBridge IOMMUs claim support for 2M and 1G superpages, but don't
+     * implement superpages internally.
+     *
+     * There are issues changing the walk length under in-flight DMA, which
+     * has manifested as incompatibility between EPT/IOMMU sharing and the
+     * workaround for CVE-2018-12207 / XSA-304.  Hide the superpages
+     * capabilities in the IOMMU, which will prevent Xen from sharing the EPT
+     * and IOMMU pagetables.
+     *
+     * Detection of SandyBridge unfortunately has to be done by processor
+     * model because the client parts don't expose their IOMMUs as PCI devices
+     * we could match with a Device ID.
+     */
+    if ( boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
+         boot_cpu_data.x86 == 6 &&
+         (boot_cpu_data.x86_model == 0x2a ||
+          boot_cpu_data.x86_model == 0x2d) )
+        iommu->cap &= ~(0xful << 34);
+}