[xen staging-4.20] domctl: handle XEN_DOMCTL_get_device_group without acquiring domctl lock

[patchbot@xxxxxxx]

commit c720b158d90c77ca629d9a60ae1ad69f46c3eb63
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Jun 4 21:39:31 2026 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Jun 4 21:39:53 2026 +0100

    domctl: handle XEN_DOMCTL_get_device_group without acquiring domctl lock
    
    iommu_get_device_group() uses its own locking. Thus, with caller side
    locking irrelevant, it can as well be called with the domctl lock not
    held.
    
    Move the handling not only ahead of acquiring the lock, but also ahead
    of the XSM check, leveraging that the sub-op has its own hook.
    
    This is part of XSA-492.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    (cherry picked from commit 471b377747cb5eb0ea7c1ca48ac9d38027a9aa13)
---
 xen/common/domctl.c           | 5 ++++-
 xen/drivers/passthrough/pci.c | 4 ++--
 xen/include/xsm/dummy.h       | 3 ++-
 xen/xsm/flask/hooks.c         | 2 +-
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 601626f061..bc46dce585 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -504,6 +504,10 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
u_domctl)
         /* Other sub-ops handled further down. */
         break;
 
+    case XEN_DOMCTL_get_device_group:
+        ret = iommu_do_domctl(op, d, u_domctl);
+        goto domctl_out_unlock_domonly;
+
     case XEN_DOMCTL_ioport_permission:
     case XEN_DOMCTL_ioport_mapping:
     case XEN_DOMCTL_gsi_permission:
@@ -927,7 +931,6 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
u_domctl)
     case XEN_DOMCTL_assign_device:
     case XEN_DOMCTL_test_assign_device:
     case XEN_DOMCTL_deassign_device:
-    case XEN_DOMCTL_get_device_group:
         ret = iommu_do_domctl(op, d, u_domctl);
         break;
 
diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
index 7410dfdfcb..f41ba30426 100644
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -1626,7 +1626,7 @@ static int iommu_get_device_group(
         if ( (pdev->seg != seg) || ((b == bus) && (df == devfn)) )
             continue;
 
-        if ( xsm_get_device_group(XSM_HOOK, (seg << 16) | (b << 8) | df) )
+        if ( xsm_get_device_group(XSM_PRIV, (seg << 16) | (b << 8) | df) )
             continue;
 
         sdev_id = iommu_call(ops, get_device_group_id, seg, b, df);
@@ -1696,7 +1696,7 @@ int iommu_do_pci_domctl(
         u32 max_sdevs;
         XEN_GUEST_HANDLE_64(uint32) sdevs;
 
-        ret = xsm_get_device_group(XSM_HOOK, 
domctl->u.get_device_group.machine_sbdf);
+        ret = xsm_get_device_group(XSM_PRIV, 
domctl->u.get_device_group.machine_sbdf);
         if ( ret )
             break;
 
diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index 2a5d14d6bf..1129b2ffc6 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -162,6 +162,7 @@ static XSM_INLINE int cf_check xsm_domctl(
     {
     case XEN_DOMCTL_bind_pt_irq:
     case XEN_DOMCTL_getdomaininfo:
+    case XEN_DOMCTL_get_device_group:
     case XEN_DOMCTL_gsi_permission:
     case XEN_DOMCTL_iomem_permission:
     case XEN_DOMCTL_ioport_mapping:
@@ -400,7 +401,7 @@ static XSM_INLINE int cf_check xsm_get_vnumainfo(
 static XSM_INLINE int cf_check xsm_get_device_group(
     XSM_DEFAULT_ARG uint32_t machine_bdf)
 {
-    XSM_ASSERT_ACTION(XSM_HOOK);
+    XSM_ASSERT_ACTION(XSM_PRIV);
     return xsm_default_action(action, current->domain, NULL);
 }
 
diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
index e9cdc45456..5561e0e8fd 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -684,6 +684,7 @@ static int cf_check flask_domctl(struct domain *d, struct 
xen_domctl *op)
     /* These have individual XSM hooks and don't make it here. */
     case XEN_DOMCTL_bind_pt_irq:
     case XEN_DOMCTL_getdomaininfo:
+    case XEN_DOMCTL_get_device_group:
     case XEN_DOMCTL_gsi_permission:
     case XEN_DOMCTL_iomem_permission:
     case XEN_DOMCTL_ioport_mapping:
@@ -702,7 +703,6 @@ static int cf_check flask_domctl(struct domain *d, struct 
xen_domctl *op)
      * These have individual XSM hooks
      * (drivers/passthrough/{pci,device_tree.c)
      */
-    case XEN_DOMCTL_get_device_group:
     case XEN_DOMCTL_test_assign_device:
     case XEN_DOMCTL_assign_device:
     case XEN_DOMCTL_deassign_device:
--
generated by git-patchbot for /home/xen/git/xen.git#staging-4.20