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

[patchbot@xxxxxxx]

commit 471b377747cb5eb0ea7c1ca48ac9d38027a9aa13
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Jun 4 20:20:44 2026 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Jun 9 12:45:56 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>
---
 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 d28626b4ca..a9816b2e58 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -513,6 +513,10 @@ 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:
@@ -923,7 +927,6 @@ 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 464bb0fee4..7991a0f91b 100644
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -1703,7 +1703,7 @@ 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);
@@ -1773,7 +1773,7 @@ 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 1dde2cd5c6..ca010387b1 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_get_domain_state:
     case XEN_DOMCTL_gsi_permission:
     case XEN_DOMCTL_iomem_permission:
@@ -394,7 +395,7 @@ 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 a7075f742b..14347ae2fd 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -653,6 +653,7 @@ 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_get_domain_state:
     case XEN_DOMCTL_gsi_permission:
     case XEN_DOMCTL_iomem_permission:
@@ -672,7 +673,6 @@ 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:
--
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