Fix previous mode detection by reading CS from the trap frame and sanitize segment restoration

xtoskrnl/ar/amd64/archsup.S

@@ -112,7 +112,7 @@ Ar\Type\Vector:
 
     /* Test previous mode and swap GS if needed */
     movl $0, TrapPreviousMode(%rbp)
-    mov %cs, %ax
+    mov TrapSegCs(%rbp), %ax
     and $3, %al
     mov %al, TrapPreviousMode(%rbp)
 
@@ -174,11 +174,6 @@ KernelModeReturn\Type\Vector:
     /* Load MxCsr register */
     ldmxcsr TrapMxCsr(%rbp)
 
-    /* Restore segment selectors */
-    mov TrapSegDs(%rbp), %ds
-    mov TrapSegEs(%rbp), %es
-    mov TrapSegFs(%rbp), %fs
-
     /* Free stack space */
     add $(TRAP_FRAME_SIZE - TRAP_REGISTERS_SIZE), %rsp
 

xtoskrnl/includes/ar/amd64/asmsup.h

@@ -56,6 +56,7 @@
 #define TrapSegEs                               330
 #define TrapSegFs                               332
 #define TrapSegGs                               334
+#define TrapSegCs                               480
 #define TrapRsp                                 496
 #define TrapSegSs                               504