# Commit 5540b94e8191059eb9cbbe98ac316232a42208f6
# Date 2024-06-13 16:53:34 +0200
# Author Jan Beulich <jbeulich@suse.com>
# Committer Jan Beulich <jbeulich@suse.com>
x86/EPT: correct special page checking in epte_get_entry_emt()

mfn_valid() granularity is (currently) 256Mb. Therefore the start of a
1Gb page passing the test doesn't necessarily mean all parts of such a
range would also pass. Yet using the result of mfn_to_page() on an MFN
which doesn't pass mfn_valid() checking is liable to result in a crash
(the invocation of mfn_to_page() alone is presumably "just" UB in such a
case).

Fixes: ca24b2ffdbd9 ("x86/hvm: set 'ipat' in EPT for special pages")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -518,8 +518,12 @@ int epte_get_entry_emt(struct domain *d,
     }
 
     for ( special_pgs = i = 0; i < (1ul << order); i++ )
-        if ( is_special_page(mfn_to_page(mfn_add(mfn, i))) )
+    {
+        mfn_t cur = mfn_add(mfn, i);
+
+        if ( mfn_valid(cur) && is_special_page(mfn_to_page(cur)) )
             special_pgs++;
+    }
 
     if ( special_pgs )
     {