x86/xen: Add UNTRAIN_RET

Ensure the Xen entry also passes through UNTRAIN_RET.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Reviewed-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>

Author: Peter Zijlstra

arch/x86/entry/entry_64.S

@@ -328,6 +328,12 @@ SYM_CODE_END(ret_from_fork)
 #endif
 .endm
 
+SYM_CODE_START_LOCAL(xen_error_entry)
+	UNWIND_HINT_FUNC
+	UNTRAIN_RET
+	RET
+SYM_CODE_END(xen_error_entry)
+
 /**
  * idtentry_body - Macro to emit code calling the C function
  * @cfunc:		C function to be called
@@ -347,7 +353,7 @@ SYM_CODE_END(ret_from_fork)
 	 * switch the CR3.  So it can skip invoking error_entry().
 	 */
 	ALTERNATIVE "call error_entry; movq %rax, %rsp", \
-		"", X86_FEATURE_XENPV
+		    "call xen_error_entry", X86_FEATURE_XENPV
 
 	ENCODE_FRAME_POINTER
 	UNWIND_HINT_REGS