CurrentPrcb is needed here

xtoskrnl/ke/amd64/proc.c

@@ -35,7 +35,7 @@ XTAPI
 PKPROCESSOR_CONTROL_BLOCK
 KeGetCurrentProcessorControlBlock(VOID)
 {
-    return (PKPROCESSOR_CONTROL_BLOCK)ArReadGSQuadWord(FIELD_OFFSET(KPROCESSOR_BLOCK, Prcb));
+    return (PKPROCESSOR_CONTROL_BLOCK)ArReadGSQuadWord(FIELD_OFFSET(KPROCESSOR_BLOCK, CurrentPrcb));
 }
 
 /**