[PATCH] tools/libxl: Only access legacy altp2m on HVM

[Jason Andryuk <jason.andryuk@xxxxxxx>]

Only access the HVM union b_info->u.hvm on HVM guests.  The union
access is not guarded, so this reads and sets the default even on
non-HVM guests.  Usually this doesn't matter as PV and PVH unions are
smaller and zero-initialized, but the zero default will be re-written as
a -1 boolean.  Generally, it it could incorrectly set b_info->altp2m
through aliased data.

Fixes: 0291089f6ea8 ("xen: enable altp2m at create domain domctl")
Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
Change-Id: Ifaca3533dcce3f409c2efa292c7e96fba6371d9d
---
 tools/libs/light/libxl_x86.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/libs/light/libxl_x86.c b/tools/libs/light/libxl_x86.c
index 0b1c2d3a96..b8f6663829 100644
--- a/tools/libs/light/libxl_x86.c
+++ b/tools/libs/light/libxl_x86.c
@@ -821,10 +821,12 @@ int libxl__arch_domain_build_info_setdefault(libxl__gc 
*gc,
      * If the legacy field info->u.hvm.altp2m is set, activate altp2m.
      * Otherwise set altp2m based on the field info->altp2m.
      */
-    libxl_defbool_setdefault(&b_info->u.hvm.altp2m, false);
-    if (b_info->altp2m == LIBXL_ALTP2M_MODE_DISABLED &&
-        libxl_defbool_val(b_info->u.hvm.altp2m))
-        b_info->altp2m = libxl_defbool_val(b_info->u.hvm.altp2m);
+    if (b_info->type == LIBXL_DOMAIN_TYPE_HVM) {
+        libxl_defbool_setdefault(&b_info->u.hvm.altp2m, false);
+        if (b_info->altp2m == LIBXL_ALTP2M_MODE_DISABLED &&
+            libxl_defbool_val(b_info->u.hvm.altp2m))
+            b_info->altp2m = libxl_defbool_val(b_info->u.hvm.altp2m);
+    }
 
     return 0;
 }
-- 
2.49.0