[xen master] x86/domctl: don't imply I/O port permissions from I/O port mapping

[patchbot@xxxxxxx]

commit 3845d3854d699feabf637580f0aa9701f209b6a7
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Jul 22 09:29:09 2026 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Jul 22 09:29:09 2026 +0200

    x86/domctl: don't imply I/O port permissions from I/O port mapping
    
    Rather than granting permissions when mapping (an operation that DM-s are
    allowed to carry out, while they can't invoke ioport-permission), check
    whether permissions actually were granted when adding a mapping. This then
    also allows relaxing the necessary locking.
    
    While no longer granting permissions upon mapping is "only" at risk of
    breaking guests, no longer revoking permissions upon unmapping strictly
    requires callers to additionally invoke XEN_DOMCTL_ioport_permission. Or
    else a security issue would arise. In-tree code already does so.
    
    While there switch to using %pd in the two log messages.
    
    Fixes: 192c4dabc344 ("domctl and p2m changes for PCI passthru")
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Roger Pau Monné <roger@xxxxxxxxxxxxxx>
    Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 CHANGELOG.md          |  5 +++++
 xen/arch/x86/domctl.c | 61 ++++++++++++++++++++++-----------------------------
 2 files changed, 31 insertions(+), 35 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 356be88351..1d3d7e0d87 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,11 @@ The format is based on [Keep a 
Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Changed
  - XEN_DOMCTL_DEV_DT's, FLASK_[GS]ETBOOL's, and FLASK_DEVICETREE_LABEL's input
    string sizes need to include the nul terminator.
+ - On x86:
+   - XEN_DOMCTL_ioport_mapping no longer implicitly grants or revokes
+     permissions for the port range in question.
+     XEN_DOMCTL_ioport_permission now needs invoking up front /
+     afterwards.
 
 ### Added
 
diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 2ecd81d89b..3100f4283c 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -714,15 +714,35 @@ long arch_do_domctl(
             break;
 
         hvm = &d->arch.hvm;
-        iocaps_double_lock(d, true);
+        /*
+         * NB: The double lock isn't really needed when !add, but is used 
anyway
+         * to keep things simple.
+         */
+        iocaps_double_lock(d, false);
 
         if ( !ioports_access_permitted(currd, fmp, fmp + np - 1) )
             ret = -EPERM;
-        else if ( add )
+        else if ( !add )
         {
             printk(XENLOG_G_INFO
-                   "ioport_map:add: dom%d gport=%x mport=%x nr=%x\n",
-                   d->domain_id, fgp, fmp, np);
+                   "ioport_map:remove: %pd gport=%x mport=%x nr=%x\n",
+                   d, fgp, fmp, np);
+
+            write_lock(&hvm->g2m_ioport_lock);
+            list_for_each_entry(g2m_ioport, &hvm->g2m_ioport_list, list)
+                if ( g2m_ioport->mport == fmp )
+                {
+                    list_del(&g2m_ioport->list);
+                    xfree(g2m_ioport);
+                    break;
+                }
+            write_unlock(&hvm->g2m_ioport_lock);
+        }
+        else if ( ioports_access_permitted(d, fmp, fmp + np - 1) )
+        {
+            printk(XENLOG_G_INFO
+                   "ioport_map:add: %pd gport=%x mport=%x nr=%x\n",
+                   d, fgp, fmp, np);
 
             write_lock(&hvm->g2m_ioport_lock);
             list_for_each_entry(g2m_ioport, &hvm->g2m_ioport_list, list)
@@ -747,40 +767,11 @@ long arch_do_domctl(
                 list_add_tail(&g2m_ioport->list, &hvm->g2m_ioport_list);
             }
             write_unlock(&hvm->g2m_ioport_lock);
-            if ( !ret )
-                ret = ioports_permit_access(d, fmp, fmp + np - 1);
-            if ( ret && !found && g2m_ioport )
-            {
-                write_lock(&hvm->g2m_ioport_lock);
-                list_del(&g2m_ioport->list);
-                write_unlock(&hvm->g2m_ioport_lock);
-                xfree(g2m_ioport);
-            }
         }
         else
-        {
-            printk(XENLOG_G_INFO
-                   "ioport_map:remove: dom%d gport=%x mport=%x nr=%x\n",
-                   d->domain_id, fgp, fmp, np);
-
-            write_lock(&hvm->g2m_ioport_lock);
-            list_for_each_entry(g2m_ioport, &hvm->g2m_ioport_list, list)
-                if ( g2m_ioport->mport == fmp )
-                {
-                    list_del(&g2m_ioport->list);
-                    xfree(g2m_ioport);
-                    break;
-                }
-            write_unlock(&hvm->g2m_ioport_lock);
-
-            ret = ioports_deny_access(d, fmp, fmp + np - 1);
-            if ( ret && is_hardware_domain(currd) )
-                printk(XENLOG_ERR
-                       "ioport_map: error %ld denying dom%d access to 
[%x,%x]\n",
-                       ret, d->domain_id, fmp, fmp + np - 1);
-        }
+            ret = -EPERM;
 
-        iocaps_double_unlock(d, true);
+        iocaps_double_unlock(d, false);
         break;
     }
 
--
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