[Xen-changelog] [xen stable-4.8] x86/vtd: Hide superpage support for SandyBridge IOMMUs

[patchbot@xxxxxxx]

commit fb93a9ba26d5e9600d2012fe4796cca82decdba1
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Oct 24 14:09:01 2019 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Nov 12 17:17:58 2019 +0000

    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@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/drivers/passthrough/vtd/extern.h |  2 ++
 xen/drivers/passthrough/vtd/iommu.c  |  2 ++
 xen/drivers/passthrough/vtd/quirks.c | 25 +++++++++++++++++++++++++
 3 files changed, 29 insertions(+)

diff --git a/xen/drivers/passthrough/vtd/extern.h 
b/xen/drivers/passthrough/vtd/extern.h
index fb7edfaef9..d698b1d50a 100644
--- 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 54cb798c2e..d1978133a0 100644
--- 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_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 5bbbd96d51..7fca95fa87 100644
--- a/xen/drivers/passthrough/vtd/quirks.c
+++ b/xen/drivers/passthrough/vtd/quirks.c
@@ -539,3 +539,28 @@ 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);
+}
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8

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