tests: add test for the mpu_noexec_ram pseudomodule

The Makefiles have been copied from the mpu_stack_guard test.

tests/mpu_noexec_ram/Makefile

@@ -0,0 +1,5 @@
+include ../Makefile.tests_common
+
+USEMODULE += mpu_noexec_ram
+
+include $(RIOTBASE)/Makefile.include

tests/mpu_noexec_ram/README.md

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+# mpu_noexec_ram
+
+Tests for the `mpu_noexec_ram` pseudomodule. As this module is currently
+only supported on Cortex M devices, the test case is a bit ARM specific.
+
+## Output
+
+With `USEMODULE += mpu_noexec_ram` in `Makefile` this application should
+execute a kernel panic from the `MEM MANAGE HANDLER`. Without this
+pseudomodule activated, it will run into a hard fault.

tests/mpu_noexec_ram/main.c

@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2020 Sören Tempel <tempel@uni-bremen.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup tests
+ * @{
+ *
+ * @file
+ * @brief Test application for the mpu_noexec_stack pseudo-module
+ *
+ * @author Sören Tempel <tempel@uni-bremen.de>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+
+#include "cpu.h"
+#include "mpu.h"
+
+/* RIOT's MPU headers gracefully fail when no MPU is present.
+ * Use this to catch if RIOT's features are correctly gating MPU use.
+ */
+#if !__MPU_PRESENT
+#error "(!__MPU_PRESENT)"
+#endif
+
+#define JMPBUF_SIZE 3
+
+int main(void)
+{
+    uint32_t buf[JMPBUF_SIZE];
+
+    /* Fill the buffer with invalid instructions */
+    for (unsigned i = 0; i < JMPBUF_SIZE; i++) {
+        buf[i] = UINT32_MAX;
+    }
+
+    puts("Attempting to jump to stack buffer ...\n");
+    __asm__ volatile ("BX %0"
+                      : /* no output operands */
+                      : "r" ((uint8_t*)&buf + 1)); /* LSB must be set for thumb2 */
+
+    return 0;
+}