[PATCH] Arm: tighten translate_get_page()

[Jan Beulich]

Permitting writes when the P2M type says "read-only" can't be correct.

Fixes: 1661158723a ("xen/arm: Extend copy_to_guest to support copying from/to 
guest physical address")
Signed-off-by: Jan Beulich <jbeul...@suse.com>
---
What exactly p2m_ram_ro means on Arm is unclear: The comment next to its
definition says one thing, its use in get_page_from_gfn() says another.
(I remember raising this point before, i.e. it feels a little odd that the
ambiguity still exists.) The patch here assumes the comment is what is
wrong.

--- a/xen/arch/arm/guestcopy.c
+++ b/xen/arch/arm/guestcopy.c
@@ -44,7 +44,7 @@ static struct page_info *translate_get_p
     if ( !page )
         return NULL;
 
-    if ( !p2m_is_ram(p2mt) )
+    if ( write ? p2mt != p2m_ram_rw : !p2m_is_ram(p2mt) )
     {
         put_page(page);
         return NULL;