[xen stable-4.18] x86/HVM: correct MMIO emulation cache bounds check

[patchbot@xxxxxxx]

commit 0d2799a557b4e08ab4eb2dada46afeb6e6f56c1f
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Feb 17 13:28:13 2025 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Feb 17 13:28:13 2025 +0100

    x86/HVM: correct MMIO emulation cache bounds check
    
    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@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    master commit: e5339bb689dfa79a914c6c96e1d82d61e1ae3161
    master date: 2025-01-23 11:14:48 +0100
---
 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 5742383139..cebd4a5161 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -937,7 +937,7 @@ 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;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.18