File xsa304-1.patch of Package xen

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>

--- a/xen/drivers/passthrough/vtd/extern.h
+++ b/xen/drivers/passthrough/vtd/extern.h
@@ -96,6 +96,8 @@ void vtd_ops_postamble_quirk(struct iomm
 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);
 
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1205,6 +1205,8 @@ int __init iommu_alloc(struct acpi_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 )
--- a/xen/drivers/passthrough/vtd/quirks.c
+++ b/xen/drivers/passthrough/vtd/quirks.c
@@ -539,3 +539,30 @@ void pci_vtd_quirk(const struct pci_dev
         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
+     * makes EPT/IOMMU sharing incompatible with the workaround for
+     * CVE-2018-12207 / XSA-304.  Furthermore, performance numbers suggest
+     * using 4k mappings is faster than 2M mappings anyway.
+     *
+     * Hide the superpages capabilities in the IOMMU.  This 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);
+}