[PATCH v2 07/17] xsm/dummy: Allow HVMOP_get_param for control domain

[Jason Andryuk <jason.andryuk@xxxxxxx>]

The Control domain is denied access to an untargetable domain.  However
init-dom0less wants to read the xenstore event channel HVM param to
determine if xenstore should be set up.

This is a read operation, so it is not modifying the domain.  Special
case the HVMOP_get_param operation for is_control_domain().  It is done
in xsm_hvm_param() because xsm_default_action() is too complicated.
HVMOP_get_param should be allowed for a domain itself (XSM_TARGET) and
its device model - src->target or is_dm_domain().  It should otherwise
be denied for untargetable domains.  xsm_default_action() doesn't have
sufficient information to identify the particular operation, so put it
in xsm_hvm_param().

Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
---
It's messy, but I couldn't think of a better way.
---
 xen/include/xsm/dummy.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index 4d7b1d61eb..896ebee631 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -621,7 +621,10 @@ 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);
+    /* Special case to allow init-dom0less to read HVM params. */
+    if ( op == HVMOP_get_param && is_control_domain(current->domain) )
+        return 0;
+    return xsm_default_action(XSM_TARGET, current->domain, d);
 }
 
 static XSM_INLINE int cf_check xsm_hvm_param_altp2mhvm(
-- 
2.50.0