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

[patchbot@xxxxxxx]

commit 6dacdcd439c1ddd32110d4a008de346e367409ec
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 17:12:54 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 6b0b7af9e2..994d360e90 100644
--- a/xen/drivers/passthrough/vtd/extern.h
+++ b/xen/drivers/passthrough/vtd/extern.h
@@ -101,6 +101,8 @@ void vtd_ops_postamble_quirk(struct vtd_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 vtd_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 68e7f5fb58..25ad649c34 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1170,6 +1170,8 @@ 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 e7e326fe8c..4dadd9523f 100644
--- a/xen/drivers/passthrough/vtd/quirks.c
+++ b/xen/drivers/passthrough/vtd/quirks.c
@@ -536,3 +536,28 @@ void pci_vtd_quirk(const struct pci_dev *pdev)
         break;
     }
 }
+
+void __init quirk_iommu_caps(struct vtd_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#master

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