[xen staging] VT-d: avoid NULL deref on domain_context_mapping_one() error paths

[patchbot@xxxxxxx]

commit 608394b906e71587f02e6662597bc985bad33a5a
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Apr 7 12:30:19 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Apr 7 12:30:19 2022 +0200

    VT-d: avoid NULL deref on domain_context_mapping_one() error paths
    
    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 non-PCI-Express devices with RMRRs
    (if such exist in practice) any longer; note that as of trhe 1st of the
    two commits referenced below assigning them to DomU-s is unsupported
    anyway.
    
    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>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/drivers/passthrough/vtd/extern.h |  2 +-
 xen/drivers/passthrough/vtd/iommu.c  | 34 +++++++++++++++++++---------------
 xen/drivers/passthrough/vtd/quirks.c |  2 +-
 3 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/xen/drivers/passthrough/vtd/extern.h 
b/xen/drivers/passthrough/vtd/extern.h
index 9ff38f3ded..39602d1f88 100644
--- a/xen/drivers/passthrough/vtd/extern.h
+++ b/xen/drivers/passthrough/vtd/extern.h
@@ -85,7 +85,7 @@ int domain_context_mapping_one(struct domain *domain, struct 
vtd_iommu *iommu,
                                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);
 
diff --git a/xen/drivers/passthrough/vtd/iommu.c 
b/xen/drivers/passthrough/vtd/iommu.c
index 4c9de8fecf..76ff551dfe 100644
--- 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 domain *domain, 
u8 devfn,
          * 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 domain *domain, 
u8 devfn,
 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;
@@ -1861,7 +1868,8 @@ 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 )
     {
@@ -1910,8 +1918,7 @@ static const struct acpi_drhd_unit *domain_context_unmap(
         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);
 
@@ -1924,8 +1931,7 @@ static const struct acpi_drhd_unit *domain_context_unmap(
         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;
 
@@ -1948,12 +1954,10 @@ static const struct acpi_drhd_unit 
*domain_context_unmap(
             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;
 
diff --git a/xen/drivers/passthrough/vtd/quirks.c 
b/xen/drivers/passthrough/vtd/quirks.c
index f6f74416d0..3ddbb20e48 100644
--- 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_function(struct 
domain *domain,
                                         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;
 }
--
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