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From 6e647efaf2b02ce92bcf80bec47c18cca5084f8a Mon Sep 17 00:00:00 2001
From: Jan Beulich <jbeulich@suse.com>
Date: Wed, 26 Jun 2024 13:39:44 +0200
Subject: [PATCH 26/56] x86/EPT: correct special page checking in
epte_get_entry_emt()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
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>
master commit: 5540b94e8191059eb9cbbe98ac316232a42208f6
master date: 2024-06-13 16:53:34 +0200
---
xen/arch/x86/mm/p2m-ept.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index 85c4e8e54f..1aa6bbc771 100644
--- 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, gfn_t gfn, mfn_t mfn,
}
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 )
{
--
2.45.2
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