Revert "x86/ftrace: Use alternative RET encoding"

This reverts commit 3eb602ad6a.

Revert the backport of upstream commit

  1f001e9da6 ("x86/ftrace: Use alternative RET encoding")

in favor of a proper backport after backporting the commit which adds
__text_gen_insn().

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/kernel/ftrace.c

@@ -311,7 +311,7 @@ union ftrace_op_code_union {
 	} __attribute__((packed));
 };
 
-#define RET_SIZE		(IS_ENABLED(CONFIG_RETPOLINE) ? 5 : 1 + IS_ENABLED(CONFIG_SLS))
+#define RET_SIZE		1 + IS_ENABLED(CONFIG_SLS)
 
 static unsigned long
 create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
@@ -367,12 +367,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 		goto fail;
 
 	ip = trampoline + size;
-
-	/* The trampoline ends with ret(q) */
-	if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
-		memcpy(ip, text_gen_insn(JMP32_INSN_OPCODE, ip, &__x86_return_thunk), JMP32_INSN_SIZE);
-	else
-		memcpy(ip, retq, sizeof(retq));
+	memcpy(ip, retq, RET_SIZE);
 
 	/* No need to test direct calls on created trampolines */
 	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {