This is useful for a combined hardware/xenstore domain that will run
init-dom0less and xenstored.  init-dom0less calls xc_hvm_param_get() to
retrieve the xenstore event channel and pfn to configure xenstore for a
guest.  With a hypervisor-allocated event channel and page, the
set_hvm_param is not needed, and the normal domid permissions will allow
xenstored to connect.

Similarly, a hyperlaunch-ed xenstore stubdom needs to read a domain's
xenstore event channel out of hvm_param.

This allows reading but not modifying the guest, so allow the permission.

Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
---
 xen/arch/arm/hvm.c      |  2 +-
 xen/arch/x86/hvm/hvm.c  |  8 ++++----
 xen/include/xsm/dummy.h | 14 ++++++++++++--
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/xen/arch/arm/hvm.c b/xen/arch/arm/hvm.c
index 86e49bf474..b50ca10cee 100644
--- a/xen/arch/arm/hvm.c
+++ b/xen/arch/arm/hvm.c
@@ -89,7 +89,7 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg)
         if ( d == NULL )
             return -ESRCH;
 
-        rc = xsm_hvm_param(XSM_TARGET, d, op);
+        rc = xsm_hvm_param(XSM_OTHER, d, op);
         if ( rc )
             goto param_fail;
 
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 969e43c2f2..f3f1002cc9 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4177,7 +4177,7 @@ static int hvm_allow_set_param(struct domain *d,
     uint64_t value;
     int rc;
 
-    rc = xsm_hvm_param(XSM_TARGET, d, HVMOP_set_param);
+    rc = xsm_hvm_param(XSM_OTHER, d, HVMOP_set_param);
     if ( rc )
         return rc;
 
@@ -4458,7 +4458,7 @@ static int hvm_allow_get_param(struct domain *d,
 {
     int rc;
 
-    rc = xsm_hvm_param(XSM_TARGET, d, HVMOP_get_param);
+    rc = xsm_hvm_param(XSM_OTHER, d, HVMOP_get_param);
     if ( rc )
         return rc;
 
@@ -5055,7 +5055,7 @@ static int hvmop_get_mem_type(
     if ( d == NULL )
         return -ESRCH;
 
-    rc = xsm_hvm_param(XSM_TARGET, d, HVMOP_get_mem_type);
+    rc = xsm_hvm_param(XSM_OTHER, d, HVMOP_get_mem_type);
     if ( rc )
         goto out;
 
@@ -5148,7 +5148,7 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg)
         if ( unlikely(d != current->domain) )
             rc = -EOPNOTSUPP;
         else if ( is_hvm_domain(d) && paging_mode_shadow(d) )
-            rc = xsm_hvm_param(XSM_TARGET, d, op);
+            rc = xsm_hvm_param(XSM_OTHER, d, op);
         if ( !rc )
             pagetable_dying(a.gpa);
 
diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index f2d6662a9d..06f4eccf5f 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -614,8 +614,18 @@ static XSM_INLINE int cf_check xsm_map_gmfn_foreign(
 static XSM_INLINE int cf_check xsm_hvm_param(
     XSM_DEFAULT_ARG struct domain *d, unsigned long op)
 {
-    XSM_ASSERT_ACTION(XSM_TARGET);
-    return xsm_default_action(action, current->domain, d);
+    XSM_ASSERT_ACTION(XSM_OTHER);
+    switch ( op )
+    {
+    case HVMOP_get_param:
+        /* A domain can query itself, or a DM can query its target. */
+        if ( !xsm_default_action(XSM_TARGET, current->domain, d) )
+            return 0;
+        /* Xenstore domain needs to be able to query for mapping. */
+        return xsm_default_action(XSM_XS_PRIV, current->domain, d);
+    default:
+        return xsm_default_action(XSM_TARGET, current->domain, d);
+    }
 }
 
 static XSM_INLINE int cf_check xsm_hvm_param_altp2mhvm(
-- 
2.48.1