[Xen-devel] [PATCH] x86/HVM: fix PM timer I/O port range version check

[Jan Beulich <jbeulich@xxxxxxxx>]

XOR-ing two arbitrary non-equal values may produce 1 even if both values
are different from both 0 and 1 (2 and 3 would fit, for example). Use OR
instead, which together with the earlier bailing upon finding
"version == old_version" achieves the intended effect.

Fixes: f0ad21c499f7 ("x86 hvm: Introduce pmtimer_change_ioport and 
HVM_PARAM_ACPI_IOPORTS_LOCATION")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/pmtimer.c
+++ b/xen/arch/x86/hvm/pmtimer.c
@@ -326,7 +326,7 @@ int pmtimer_change_ioport(struct domain
         return 0;
 
     /* Only allow changes between versions 0 and 1. */
-    if ( (version ^ old_version) != 1 )
+    if ( (version | old_version) != 1 )
         return -EINVAL;
 
     if ( version == 1 )

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