passthrough: quarantine PCI devices

When a PCI device is assigned to an untrusted domain, it is possible for
that domain to program the device to DMA to an arbitrary address. The
IOMMU is used to protect the host from malicious DMA by making sure that
the device addresses can only target memory assigned to the guest. However,
when the guest domain is torn down the device is assigned back to dom0,
thus allowing any in-flight DMA to potentially target critical host data.

This patch introduces a 'quarantine' for PCI devices using dom_io. When
the toolstack makes a device assignable (by binding it to pciback), it
will now also assign it to DOMID_IO and the device will only be assigned
back to dom0 when the device is made unassignable again. Whilst device is
assignable it will only ever transfer between dom_io and guest domains.
dom_io is actually only used as a sentinel domain for quarantining purposes;
it is not configured with any IOMMU mappings. Assignment to dom_io simply
means that the device's initiator (requestor) identifier is not present in
the IOMMU's device table and thus any DMA transactions issued will be
terminated with a fault condition.

In addition, a fix to assignment handling is made for VT-d.  Failure
during the assignment step should not lead to a device still being
associated with its prior owner. Hand the device to DomIO temporarily,
until the assignment step has completed successfully.  Remove the PI
hooks from the source domain then earlier as well.

Failure of the recovery reassign_device_ownership() may not go silent:
There e.g. may still be left over RMRR mappings in the domain assignment
to which has failed, and hence we can't allow that domain to continue
executing.

NOTE: This patch also includes one printk() cleanup; the
      "XEN_DOMCTL_assign_device: " tag is dropped in iommu_do_pci_domctl(),
      since similar printk()-s elsewhere also don't log such a tag.

This is XSA-302.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
master commit: 319f9a0ba94c7db505cd5dd9cb0b037ab1aa8e12
master date: 2019-10-31 16:20:05 +0100

diff --git a/tools/libxl/libxl_pci.c b/tools/libxl/libxl_pci.c
index 4755a0c93cfb7927d5ee479e193bfcb322254b0d..81890a91ace59aba6892000f77511b03aed51e43 100644 (file)
--- a/tools/libxl/libxl_pci.c
+++ b/tools/libxl/libxl_pci.c
@@ -754,6 +754,7 @@ static int libxl__device_pci_assignable_add(libxl__gc *gc,
                                             libxl_device_pci *pcidev,
                                             int rebind)
 {
+    libxl_ctx *ctx = libxl__gc_owner(gc);
     unsigned dom, bus, dev, func;
     char *spath, *driver_path = NULL;
     int rc;
@@ -779,7 +780,7 @@ static int libxl__device_pci_assignable_add(libxl__gc *gc,
     }
     if ( rc ) {
         LOG(WARN, PCI_BDF" already assigned to pciback", dom, bus, dev, func);
-        return 0;
+        goto quarantine;
     }
 
     /* Check to see if there's already a driver that we need to unbind from */
@@ -810,6 +811,19 @@ static int libxl__device_pci_assignable_add(libxl__gc *gc,
         return ERROR_FAIL;
     }
 
+quarantine:
+    /*
+     * DOMID_IO is just a sentinel domain, without any actual mappings,
+     * so always pass XEN_DOMCTL_DEV_RDM_RELAXED to avoid assignment being
+     * unnecessarily denied.
+     */
+    rc = xc_assign_device(ctx->xch, DOMID_IO, pcidev_encode_bdf(pcidev),
+                          XEN_DOMCTL_DEV_RDM_RELAXED);
+    if ( rc < 0 ) {
+        LOG(ERROR, "failed to quarantine "PCI_BDF, dom, bus, dev, func);
+        return ERROR_FAIL;
+    }
+
     return 0;
 }
 
@@ -817,9 +831,18 @@ static int libxl__device_pci_assignable_remove(libxl__gc *gc,
                                                libxl_device_pci *pcidev,
                                                int rebind)
 {
+    libxl_ctx *ctx = libxl__gc_owner(gc);
     int rc;
     char *driver_path;
 
+    /* De-quarantine */
+    rc = xc_deassign_device(ctx->xch, DOMID_IO, pcidev_encode_bdf(pcidev));
+    if ( rc < 0 ) {
+        LOG(ERROR, "failed to de-quarantine "PCI_BDF, pcidev->domain, pcidev->bus,
+            pcidev->dev, pcidev->func);
+        return ERROR_FAIL;
+    }
+
     /* Unbind from pciback */
     if ( (rc=pciback_dev_is_assigned(gc, pcidev)) < 0 ) {
         return ERROR_FAIL;

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index c701c7ef143cbc48bc01d6895a9542a8b2c8b1f7..f46f05d3cca496a67449181740309f1949c865ac 100644 (file)
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -295,9 +295,11 @@ void __init arch_init_memory(void)
      * Initialise our DOMID_IO domain.
      * This domain owns I/O pages that are within the range of the page_info
      * array. Mappings occur at the priv of the caller.
+     * Quarantined PCI devices will be associated with this domain.
      */
     dom_io = domain_create(DOMID_IO, NULL);
     BUG_ON(IS_ERR(dom_io));
+    INIT_LIST_HEAD(&dom_io->arch.pdev_list);
 
     /*
      * Initialise our COW domain.

diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 9b7bc083eeed5ab0141353ad92f83447c9b02935..741d774cd19da4d984ef21c91649e9d95f321d2d 100644 (file)
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -392,6 +392,16 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
 
     switch ( op->cmd )
     {
+    case XEN_DOMCTL_assign_device:
+    case XEN_DOMCTL_deassign_device:
+        if ( op->domain == DOMID_IO )
+        {
+            d = dom_io;
+            break;
+        }
+        else if ( op->domain == DOMID_INVALID )
+            return -ESRCH;
+        /* fall through */
     case XEN_DOMCTL_test_assign_device:
         if ( op->domain == DOMID_INVALID )
         {
@@ -413,7 +423,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
 
     if ( !domctl_lock_acquire() )
     {
-        if ( d )
+        if ( d && d != dom_io )
             rcu_unlock_domain(d);
         return hypercall_create_continuation(
             __HYPERVISOR_domctl, "h", u_domctl);
@@ -1148,7 +1158,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
     domctl_lock_release();
 
  domctl_out_unlock_domonly:
-    if ( d )
+    if ( d && d != dom_io )
         rcu_unlock_domain(d);
 
     if ( copyback && __copy_to_guest(u_domctl, op, 1) )

diff --git a/xen/drivers/passthrough/amd/pci_amd_iommu.c b/xen/drivers/passthrough/amd/pci_amd_iommu.c
index 12d2695b89e568b4cbcd6c4876fc30e945c11d16..ec8baae717738caa486c60319be397ce83dc5140 100644 (file)
--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c
@@ -118,6 +118,10 @@ static void amd_iommu_setup_domain_device(
     u8 bus = pdev->bus;
     const struct domain_iommu *hd = dom_iommu(domain);
 
+    /* dom_io is used as a sentinel for quarantined devices */
+    if ( domain == dom_io )
+        return;
+
     BUG_ON( !hd->arch.root_table || !hd->arch.paging_mode ||
             !iommu->dev_table.buffer );
 
@@ -305,6 +309,10 @@ void amd_iommu_disable_domain_device(struct domain *domain,
     int req_id;
     u8 bus = pdev->bus;
 
+    /* dom_io is used as a sentinel for quarantined devices */
+    if ( domain == dom_io )
+        return;
+
     BUG_ON ( iommu->dev_table.buffer == NULL );
     req_id = get_dma_requestor_id(iommu->seg, PCI_BDF2(bus, devfn));
     dte = iommu->dev_table.buffer + (req_id * IOMMU_DEV_TABLE_ENTRY_SIZE);
@@ -391,7 +399,7 @@ static int amd_iommu_assign_device(struct domain *d, u8 devfn,
             ivrs_mappings[req_id].read_permission);
     }
 
-    return reassign_device(hardware_domain, d, devfn, pdev);
+    return reassign_device(pdev->domain, d, devfn, pdev);
 }
 
 static void deallocate_next_page_table(struct page_info *pg, int level)

diff --git a/xen/drivers/passthrough/device_tree.c b/xen/drivers/passthrough/device_tree.c
index 421f00343826ac193c0c7fd20af19c47c7675594..1cd878f583f99ffe6615b5f6ab21417853478b71 100644 (file)
--- a/xen/drivers/passthrough/device_tree.c
+++ b/xen/drivers/passthrough/device_tree.c
@@ -175,6 +175,9 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct domain *d,
             break;
         }
 
+        if ( d == dom_io )
+            return -EINVAL;
+
         ret = iommu_assign_dt_device(d, dev);
 
         if ( ret )
@@ -200,6 +203,9 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct domain *d,
 
         ret = xsm_deassign_dtdevice(XSM_HOOK, d, dt_node_full_name(dev));
 
+        if ( d == dom_io )
+            return -EINVAL;
+
         ret = iommu_deassign_dt_device(d, dev);
 
         if ( ret )

diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index 04b0be37d3e436fde84fa7751138e50547737657..8027d96f1c9940c65db8bf4acd6d1352d7262b5f 100644 (file)
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -219,6 +219,9 @@ void iommu_teardown(struct domain *d)
 {
     const struct domain_iommu *hd = dom_iommu(d);
 
+    if ( d == dom_io )
+        return;
+
     d->need_iommu = 0;
     hd->platform_ops->teardown(d);
     tasklet_schedule(&iommu_pt_cleanup_tasklet);
@@ -229,6 +232,9 @@ int iommu_construct(struct domain *d)
     if ( need_iommu(d) > 0 )
         return 0;
 
+    if ( d == dom_io )
+        return 0;
+
     if ( !iommu_use_hap_pt(d) )
     {
         int rc;
@@ -404,6 +410,9 @@ int __init iommu_setup(void)
     printk("I/O virtualisation %sabled\n", iommu_enabled ? "en" : "dis");
     if ( iommu_enabled )
     {
+        if ( iommu_domain_init(dom_io) )
+            panic("Could not set up quarantine\n");
+
         printk(" - Dom0 mode: %s\n",
                iommu_passthrough ? "Passthrough" :
                iommu_dom0_strict ? "Strict" : "Relaxed");

diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
index f73123761df21ebf19f67a9bbf8b8f8cc209fc62..b7b8aea9a33e7ded04f3153a23fd9d87c777d065 100644 (file)
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -1389,19 +1389,29 @@ static int iommu_remove_device(struct pci_dev *pdev)
     return hd->platform_ops->remove_device(pdev->devfn, pci_to_dev(pdev));
 }
 
-/*
- * If the device isn't owned by the hardware domain, it means it already
- * has been assigned to other domain, or it doesn't exist.
- */
 static int device_assigned(u16 seg, u8 bus, u8 devfn)
 {
     struct pci_dev *pdev;
+    int rc = 0;
 
     pcidevs_lock();
-    pdev = pci_get_pdev_by_domain(hardware_domain, seg, bus, devfn);
+
+    pdev = pci_get_pdev(seg, bus, devfn);
+
+    if ( !pdev )
+        rc = -ENODEV;
+    /*
+     * If the device exists and it is not owned by either the hardware
+     * domain or dom_io then it must be assigned to a guest, or be
+     * hidden (owned by dom_xen).
+     */
+    else if ( pdev->domain != hardware_domain &&
+              pdev->domain != dom_io )
+        rc = -EBUSY;
+
     pcidevs_unlock();
 
-    return pdev ? 0 : -EBUSY;
+    return rc;
 }
 
 static int assign_device(struct domain *d, u16 seg, u8 bus, u8 devfn, u32 flag)
@@ -1415,7 +1425,7 @@ static int assign_device(struct domain *d, u16 seg, u8 bus, u8 devfn, u32 flag)
 
     /* Prevent device assign if mem paging or mem sharing have been 
      * enabled for this domain */
-    if ( unlikely(!need_iommu(d) &&
+    if ( unlikely(!need_iommu(d) && d != dom_io &&
             ((is_hvm_domain(d) &&
               d->arch.hvm_domain.mem_sharing_enabled) ||
              vm_event_check_ring(d->vm_event_paging) ||
@@ -1432,12 +1442,20 @@ static int assign_device(struct domain *d, u16 seg, u8 bus, u8 devfn, u32 flag)
         return rc;
     }
 
-    pdev = pci_get_pdev_by_domain(hardware_domain, seg, bus, devfn);
+    pdev = pci_get_pdev(seg, bus, devfn);
+
+    rc = -ENODEV;
     if ( !pdev )
-    {
-        rc = pci_get_pdev(seg, bus, devfn) ? -EBUSY : -ENODEV;
         goto done;
-    }
+
+    rc = 0;
+    if ( d == pdev->domain )
+        goto done;
+
+    rc = -EBUSY;
+    if ( pdev->domain != hardware_domain &&
+         pdev->domain != dom_io )
+        goto done;
 
     if ( pdev->msix )
     {
@@ -1465,6 +1483,10 @@ static int assign_device(struct domain *d, u16 seg, u8 bus, u8 devfn, u32 flag)
     }
 
  done:
+    /* The device is assigned to dom_io so mark it as quarantined */
+    if ( !rc && d == dom_io )
+        pdev->quarantine = true;
+
     if ( !has_arch_pdevs(d) && need_iommu(d) )
         iommu_teardown(d);
     pcidevs_unlock();
@@ -1477,6 +1499,7 @@ int deassign_device(struct domain *d, u16 seg, u8 bus, u8 devfn)
 {
     const struct domain_iommu *hd = dom_iommu(d);
     struct pci_dev *pdev = NULL;
+    struct domain *target;
     int ret = 0;
 
     if ( !iommu_enabled || !hd->platform_ops )
@@ -1487,12 +1510,16 @@ int deassign_device(struct domain *d, u16 seg, u8 bus, u8 devfn)
     if ( !pdev )
         return -ENODEV;
 
+    /* De-assignment from dom_io should de-quarantine the device */
+    target = (pdev->quarantine && pdev->domain != dom_io) ?
+        dom_io : hardware_domain;
+
     while ( pdev->phantom_stride )
     {
         devfn += pdev->phantom_stride;
         if ( PCI_SLOT(devfn) != PCI_SLOT(pdev->devfn) )
             break;
-        ret = hd->platform_ops->reassign_device(d, hardware_domain, devfn,
+        ret = hd->platform_ops->reassign_device(d, target, devfn,
                                                 pci_to_dev(pdev));
         if ( !ret )
             continue;
@@ -1503,7 +1530,7 @@ int deassign_device(struct domain *d, u16 seg, u8 bus, u8 devfn)
     }
 
     devfn = pdev->devfn;
-    ret = hd->platform_ops->reassign_device(d, hardware_domain, devfn,
+    ret = hd->platform_ops->reassign_device(d, target, devfn,
                                             pci_to_dev(pdev));
     if ( ret )
     {
@@ -1513,6 +1540,9 @@ int deassign_device(struct domain *d, u16 seg, u8 bus, u8 devfn)
         return ret;
     }
 
+    if ( pdev->domain == hardware_domain  )
+        pdev->quarantine = false;
+
     pdev->fault.count = 0;
 
     if ( !has_arch_pdevs(d) && need_iommu(d) )
@@ -1691,7 +1721,7 @@ int iommu_do_pci_domctl(
             ret = hypercall_create_continuation(__HYPERVISOR_domctl,
                                                 "h", u_domctl);
         else if ( ret )
-            printk(XENLOG_G_ERR "XEN_DOMCTL_assign_device: "
+            printk(XENLOG_G_ERR
                    "assign %04x:%02x:%02x.%u to dom%d failed (%d)\n",
                    seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn),
                    d->domain_id, ret);

diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index 4c719d4ee71ce9e5b6796b78f09e514f6ffd722a..f242e30caf2e5f6f16a9f52a9801f8da747bb007 100644 (file)
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1338,6 +1338,10 @@ int domain_context_mapping_one(
     int agaw, rc, ret;
     bool_t flush_dev_iotlb;
 
+    /* dom_io is used as a sentinel for quarantined devices */
+    if ( domain == dom_io )
+        return 0;
+
     ASSERT(pcidevs_locked());
     spin_lock(&iommu->lock);
     maddr = bus_to_context_maddr(iommu, bus);
@@ -1573,6 +1577,10 @@ int domain_context_unmap_one(
     int iommu_domid, rc, ret;
     bool_t flush_dev_iotlb;
 
+    /* dom_io is used as a sentinel for quarantined devices */
+    if ( domain == dom_io )
+        return 0;
+
     ASSERT(pcidevs_locked());
     spin_lock(&iommu->lock);
 
@@ -1705,6 +1713,10 @@ static int domain_context_unmap(struct domain *domain, u8 devfn,
         goto out;
     }
 
+    /* dom_io is used as a sentinel for quarantined devices */
+    if ( domain == dom_io )
+        goto out;
+
     /*
      * if no other devices under the same iommu owned by this domain,
      * clear iommu in iommu_bitmap and clear domain_id in domid_bitmp
@@ -2389,6 +2401,15 @@ static int reassign_device_ownership(
     if ( ret )
         return ret;
 
+    if ( devfn == pdev->devfn && pdev->domain != dom_io )
+    {
+        list_move(&pdev->domain_list, &dom_io->arch.pdev_list);
+        pdev->domain = dom_io;
+    }
+
+    if ( !has_arch_pdevs(source) )
+        vmx_pi_hooks_deassign(source);
+
     if ( !has_arch_pdevs(target) )
         vmx_pi_hooks_assign(target);
 
@@ -2401,21 +2422,19 @@ static int reassign_device_ownership(
         return ret;
     }
 
-    if ( devfn == pdev->devfn )
+    if ( devfn == pdev->devfn && pdev->domain != target )
     {
         list_move(&pdev->domain_list, &target->arch.pdev_list);
         pdev->domain = target;
     }
 
-    if ( !has_arch_pdevs(source) )
-        vmx_pi_hooks_deassign(source);
-
     return ret;
 }
 
 static int intel_iommu_assign_device(
     struct domain *d, u8 devfn, struct pci_dev *pdev, u32 flag)
 {
+    struct domain *s = pdev->domain;
     struct acpi_rmrr_unit *rmrr;
     int ret = 0, i;
     u16 bdf, seg;
@@ -2458,8 +2477,8 @@ static int intel_iommu_assign_device(
         }
     }
 
-    ret = reassign_device_ownership(hardware_domain, d, devfn, pdev);
-    if ( ret )
+    ret = reassign_device_ownership(s, d, devfn, pdev);
+    if ( ret || d == dom_io )
         return ret;
 
     /* Setup rmrr identity mapping */
@@ -2472,11 +2491,20 @@ static int intel_iommu_assign_device(
             ret = rmrr_identity_mapping(d, 1, rmrr, flag);
             if ( ret )
             {
-                reassign_device_ownership(d, hardware_domain, devfn, pdev);
+                int rc;
+
+                rc = reassign_device_ownership(d, s, devfn, pdev);
                 printk(XENLOG_G_ERR VTDPREFIX
                        " cannot map reserved region (%"PRIx64",%"PRIx64"] for Dom%d (%d)\n",
                        rmrr->base_address, rmrr->end_address,
                        d->domain_id, ret);
+                if ( rc )
+                {
+                    printk(XENLOG_ERR VTDPREFIX
+                           " failed to reclaim %04x:%02x:%02x.%u from %pd (%d)\n",
+                           seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn), d, rc);
+                    domain_crash(d);
+                }
                 break;
             }
         }

diff --git a/xen/include/xen/pci.h b/xen/include/xen/pci.h
index 4cfa7746154061155cab9d8323b91d25cee86c7e..066364bdefc2c1f434410c2a07049f08f17e20f2 100644 (file)
--- a/xen/include/xen/pci.h
+++ b/xen/include/xen/pci.h
@@ -88,6 +88,9 @@ struct pci_dev {
 
     nodeid_t node; /* NUMA node */
 
+    /* Device to be quarantined, don't automatically re-assign to dom0 */
+    bool quarantine;
+
     enum pdev_type {
         DEV_TYPE_PCI_UNKNOWN,
         DEV_TYPE_PCIe_ENDPOINT,