target/nios2: Check supervisor on eret

eret instruction is only allowed in supervisor mode.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Amir Gonnen <amir.gonnen@neuroblade.ai>
Message-Id: <20220303153906.2024748-2-amir.gonnen@neuroblade.ai>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220421151735.31996-14-richard.henderson@linaro.org>

target/nios2/translate.c

@@ -384,6 +384,8 @@ static const Nios2Instruction i_type_instructions[] = {
  */
 static void eret(DisasContext *dc, uint32_t code, uint32_t flags)
 {
+    gen_check_supervisor(dc);
+
     tcg_gen_mov_tl(cpu_R[CR_STATUS], cpu_R[CR_ESTATUS]);
     tcg_gen_mov_tl(cpu_R[R_PC], cpu_R[R_EA]);