[PATCH v2 1/2] VT-d: avoid NULL deref on domain_context_mapping_one() error paths

[Jan Beulich <jbeulich@xxxxxxxx>]

First there's a printk() which actually wrongly uses pdev in the first
place: We want to log the coordinates of the (perhaps fake) device
acted upon, which may not be pdev.

Then it was quite pointless for eb19326a328d ("VT-d: prepare for per-
device quarantine page tables (part I)") to add a domid_t parameter to
domain_context_unmap_one(): It's only used to pass back here via
me_wifi_quirk() -> map_me_phantom_function(). Drop the parameter again.

Finally there's the invocation of domain_context_mapping_one(), which
needs to be passed the correct domain ID. Avoid taking that path when
pdev is NULL and the quarantine state is what would need restoring to.
This means we can't security-support PCI devices with RMRRs (if such
exist in practice) any longer.

Fixes: 8f41e481b485 ("VT-d: re-assign devices directly")
Fixes: 14dd241aad8a ("IOMMU/x86: use per-device page tables for quarantining")
Coverity ID: 1503784
Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Drop SUPPORT.md addition. Adjust comment. Extend another comment.

--- a/xen/drivers/passthrough/vtd/extern.h
+++ b/xen/drivers/passthrough/vtd/extern.h
@@ -85,7 +85,7 @@ int domain_context_mapping_one(struct do
                                const struct pci_dev *pdev, domid_t domid,
                                paddr_t pgd_maddr, unsigned int mode);
 int domain_context_unmap_one(struct domain *domain, struct vtd_iommu *iommu,
-                             uint8_t bus, uint8_t devfn, domid_t domid);
+                             uint8_t bus, uint8_t devfn);
 int cf_check intel_iommu_get_reserved_device_memory(
     iommu_grdm_t *func, void *ctxt);
 
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1533,7 +1533,7 @@ int domain_context_mapping_one(
                 check_cleanup_domid_map(domain, pdev, iommu);
             printk(XENLOG_ERR
                    "%pp: unexpected context entry %016lx_%016lx (expected 
%016lx_%016lx)\n",
-                   &PCI_SBDF3(pdev->seg, pdev->bus, devfn),
+                   &PCI_SBDF3(seg, bus, devfn),
                    (uint64_t)(res >> 64), (uint64_t)res,
                    (uint64_t)(old >> 64), (uint64_t)old);
             rc = -EILSEQ;
@@ -1601,9 +1601,14 @@ int domain_context_mapping_one(
 
     if ( rc )
     {
-        if ( !prev_dom )
-            ret = domain_context_unmap_one(domain, iommu, bus, devfn,
-                                           DEVICE_DOMID(domain, pdev));
+        if ( !prev_dom ||
+             /*
+              * Unmapping here means DEV_TYPE_PCI devices with RMRRs (if such
+              * exist) would cause problems if such a region was actually
+              * accessed.
+              */
+             (prev_dom == dom_io && !pdev) )
+            ret = domain_context_unmap_one(domain, iommu, bus, devfn);
         else if ( prev_dom != domain ) /* Avoid infinite recursion. */
             ret = domain_context_mapping_one(prev_dom, iommu, bus, devfn, pdev,
                                              DEVICE_DOMID(prev_dom, pdev),
@@ -1744,7 +1749,9 @@ static int domain_context_mapping(struct
          * Strictly speaking if the device is the only one behind this bridge
          * and the only one with this (secbus,0,0) tuple, it could be allowed
          * to be re-assigned regardless of RMRR presence.  But let's deal with
-         * that case only if it is actually found in the wild.
+         * that case only if it is actually found in the wild.  Note that
+         * dealing with this just here would still not render the operation
+         * secure.
          */
         else if ( prev_present && (mode & MAP_WITH_RMRR) &&
                   domain != pdev->domain )
@@ -1809,7 +1816,7 @@ static int domain_context_mapping(struct
 int domain_context_unmap_one(
     struct domain *domain,
     struct vtd_iommu *iommu,
-    uint8_t bus, uint8_t devfn, domid_t domid)
+    uint8_t bus, uint8_t devfn)
 {
     struct context_entry *context, *context_entries;
     u64 maddr;
@@ -1867,7 +1874,8 @@ int domain_context_unmap_one(
     unmap_vtd_domain_page(context_entries);
 
     if ( !iommu->drhd->segment && !rc )
-        rc = me_wifi_quirk(domain, bus, devfn, domid, 0, 
UNMAP_ME_PHANTOM_FUNC);
+        rc = me_wifi_quirk(domain, bus, devfn, DOMID_INVALID, 0,
+                           UNMAP_ME_PHANTOM_FUNC);
 
     if ( rc && !is_hardware_domain(domain) && domain != dom_io )
     {
@@ -1916,8 +1924,7 @@ static const struct acpi_drhd_unit *doma
         if ( iommu_debug )
             printk(VTDPREFIX "%pd:PCIe: unmap %pp\n",
                    domain, &PCI_SBDF3(seg, bus, devfn));
-        ret = domain_context_unmap_one(domain, iommu, bus, devfn,
-                                       DEVICE_DOMID(domain, pdev));
+        ret = domain_context_unmap_one(domain, iommu, bus, devfn);
         if ( !ret && devfn == pdev->devfn && ats_device(pdev, drhd) > 0 )
             disable_ats_device(pdev);
 
@@ -1930,8 +1937,7 @@ static const struct acpi_drhd_unit *doma
         if ( iommu_debug )
             printk(VTDPREFIX "%pd:PCI: unmap %pp\n",
                    domain, &PCI_SBDF3(seg, bus, devfn));
-        ret = domain_context_unmap_one(domain, iommu, bus, devfn,
-                                       DEVICE_DOMID(domain, pdev));
+        ret = domain_context_unmap_one(domain, iommu, bus, devfn);
         if ( ret )
             break;
 
@@ -1954,12 +1960,10 @@ static const struct acpi_drhd_unit *doma
             break;
         }
 
-        ret = domain_context_unmap_one(domain, iommu, tmp_bus, tmp_devfn,
-                                       DEVICE_DOMID(domain, pdev));
+        ret = domain_context_unmap_one(domain, iommu, tmp_bus, tmp_devfn);
         /* PCIe to PCI/PCIx bridge */
         if ( !ret && pdev_type(seg, tmp_bus, tmp_devfn) == 
DEV_TYPE_PCIe2PCI_BRIDGE )
-            ret = domain_context_unmap_one(domain, iommu, secbus, 0,
-                                           DEVICE_DOMID(domain, pdev));
+            ret = domain_context_unmap_one(domain, iommu, secbus, 0);
 
         break;
 
--- a/xen/drivers/passthrough/vtd/quirks.c
+++ b/xen/drivers/passthrough/vtd/quirks.c
@@ -427,7 +427,7 @@ static int __must_check map_me_phantom_f
                                         domid, pgd_maddr, mode);
     else
         rc = domain_context_unmap_one(domain, drhd->iommu, 0,
-                                      PCI_DEVFN(dev, 7), domid);
+                                      PCI_DEVFN(dev, 7));
 
     return rc;
 }