From e5339bb689dfa79a914c6c96e1d82d61e1ae3161 Mon Sep 17 00:00:00 2001
From: Jan Beulich <jbeulich@suse.com>
Date: Thu, 23 Jan 2025 11:14:48 +0100
Subject: [PATCH] x86/HVM: correct MMIO emulation cache bounds check
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To avoid overrunning the internal buffer we need to take the offset into
the buffer into account.

Fixes: d95da91fb497 ("x86/HVM: grow MMIO cache data size to 64 bytes")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
---
 xen/arch/x86/hvm/emulate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index a1935a1748..f3b5800d81 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -935,7 +935,7 @@ static int hvmemul_phys_mmio_access(
     }
 
     /* Accesses must not overflow the cache's buffer. */
-    if ( size > sizeof(cache->buffer) )
+    if ( offset + size > sizeof(cache->buffer) )
     {
         ASSERT_UNREACHABLE();
         return X86EMUL_UNHANDLEABLE;
-- 
2.39.5