[RFC] samples: Add a self-protection test suite

tests/kernel/protection/Makefile

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+BOARD ?= frdm_k64f
+CONF_FILE = prj.conf
+
+include ${ZEPHYR_BASE}/Makefile.test

tests/kernel/protection/README.rst

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+.. _protection_tests:
+
+Protection tests
+#################################
+
+Overview
+********
+This test case verifies that protection is provided
+against the following security issues:
+
+* Write to read-only data.
+* Write to text.
+* Execute from data.
+* Execute from stack.
+* Execute from heap.
+
+Building and Running
+********************
+
+This project can be built and executed as follows:
+
+.. code-block:: console
+
+   $ cd tests/protection
+   $ make BOARD=<insert your board here>
+
+Connect the board to your host computer using the USB port.
+Flash the generated zephyr.bin on the board.
+Reset the board.
+
+Sample Output
+=============
+
+.. code-block:: console
+
+   ***** BOOTING ZEPHYR OS v1.8.99 - BUILD: Jun 19 2017 12:44:27 *****
+   Running test suite test_protection
+   tc_start() - write_ro
+   trying to write to rodata at 0x00003124
+   ***** BUS FAULT *****
+     Executing thread ID (thread): 0x200001bc
+     Faulting instruction address:  0x88c
+     Imprecise data bus error
+   Caught system error -- reason 0
+   ===================================================================
+   PASS - write_ro.
+   tc_start() - write_text
+   trying to write to text at 0x000006c0
+   ***** BUS FAULT *****
+     Executing thread ID (thread): 0x200001bc
+     Faulting instruction address:  0xd60
+     Imprecise data bus error
+   Caught system error -- reason 0
+   ===================================================================
+   PASS - write_text.
+   tc_start() - exec_data
+   trying to call code written to 0x2000041d
+   ***** BUS FAULT *****
+     Executing thread ID (thread): 0x200001bc
+     Faulting instruction address:  0x2000041c
+     Imprecise data bus error
+   Caught system error -- reason 0
+   ===================================================================
+   PASS - exec_data.
+   tc_start() - exec_stack
+   trying to call code written to 0x20000929
+   ***** BUS FAULT *****
+     Executing thread ID (thread): 0x200001bc
+     Faulting instruction address:  0x20000928
+     Imprecise data bus error
+   Caught system error -- reason 0
+   ===================================================================
+   PASS - exec_stack.
+   tc_start() - exec_heap
+   trying to call code written to 0x20000455
+   ***** BUS FAULT *****
+     Executing thread ID (thread): 0x200001bc
+     Faulting instruction address:  0x20000454
+     Imprecise data bus error
+   Caught system error -- reason 0
+   ===================================================================
+   PASS - exec_heap.
+   ===================================================================
+   PROJECT EXECUTION SUCCESSFUL

tests/kernel/protection/prj.conf

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+CONFIG_HEAP_MEM_POOL_SIZE=256
+CONFIG_ZTEST=y

tests/kernel/protection/src/Makefile

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+include $(ZEPHYR_BASE)/tests/Makefile.test
+
+ccflags-y += -I${ZEPHYR_BASE}/tests/include
+
+obj-y = targets.o main.o

tests/kernel/protection/src/main.c

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+/*
+ * Parts derived from tests/kernel/fatal/src/main.c, which has the
+ * following copyright and license:
+ *
+ * Copyright (c) 2017 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr.h>
+#include <ztest.h>
+#include <kernel_structs.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include "targets.h"
+
+#define INFO(fmt, ...) printk(fmt, ##__VA_ARGS__)
+
+/* ARM is a special case, in that k_thread_abort() does indeed return
+ * instead of calling _Swap() directly. The PendSV exception is queued
+ * and immediately fires upon completing the exception path; the faulting
+ * thread is never run again.
+ */
+#ifndef CONFIG_ARM
+FUNC_NORETURN
+#endif
+void _SysFatalErrorHandler(unsigned int reason, const NANO_ESF *pEsf)
+{
+	INFO("Caught system error -- reason %d\n", reason);
+	ztest_test_pass();
+#ifndef CONFIG_ARM
+	CODE_UNREACHABLE;
+#endif
+}
+
+#ifdef CONFIG_CPU_CORTEX_M
+#include <arch/arm/cortex_m/cmsis.h>
+/* Must clear LSB of function address to access as data. */
+#define FUNC_TO_PTR(x) (void *)((uintptr_t)(x) & ~0x1)
+/* Must set LSB of function address to call in Thumb mode. */
+#define PTR_TO_FUNC(x) (int (*)(int))((uintptr_t)(x) | 0x1)
+/* Flush preceding data writes and instruction fetches. */
+#define DO_BARRIERS() do { __DSB(); __ISB(); } while (0)
+#else
+#define FUNC_TO_PTR(x) (void *)(x)
+#define PTR_TO_FUNC(x) (int (*)(int))(x)
+#define DO_BARRIERS() do { } while (0)
+#endif
+
+static int __attribute__((noinline)) add_one(int i)
+{
+	return (i + 1);
+}
+
+static void execute_from_buffer(u8_t *dst)
+{
+	void *src = FUNC_TO_PTR(add_one);
+	int (*func)(int i) = PTR_TO_FUNC(dst);
+	int i = 1;
+
+	/* Copy add_one() code to destination buffer. */
+	memcpy(dst, src, BUF_SIZE);
+	DO_BARRIERS();
+
+	/*
+	 * Try executing from buffer we just filled.
+	 * Optimally, this triggers a fault.
+	 * If not, we check to see if the function
+	 * returned the expected result as confirmation
+	 * that we truly executed the code we wrote.
+	 */
+	INFO("trying to call code written to %p\n", func);
+	i = func(i);
+	INFO("returned from code at %p\n", func);
+	if (i == 2) {
+		INFO("Execute from target buffer succeeded!\n");
+	} else {
+		INFO("Did not get expected return value!\n");
+	}
+}
+
+static void write_ro(void)
+{
+	u32_t *ptr = (u32_t *)&rodata_var;
+
+	/*
+	 * Try writing to rodata.  Optimally, this triggers a fault.
+	 * If not, we check to see if the rodata value actually changed.
+	 */
+	INFO("trying to write to rodata at %p\n", ptr);
+	*ptr = ~RODATA_VALUE;
+
+	DO_BARRIERS();
+
+	if (*ptr == RODATA_VALUE) {
+		INFO("rodata value still the same\n");
+	} else if (*ptr == ~RODATA_VALUE) {
+		INFO("rodata modified!\n");
+	} else {
+		INFO("something went wrong!\n");
+	}
+
+	zassert_unreachable("Write to rodata did not fault");
+}
+
+static void write_text(void)
+{
+	void *src = FUNC_TO_PTR(add_one);
+	void *dst = FUNC_TO_PTR(overwrite_target);
+	int i = 1;
+
+	/*
+	 * Try writing to a function in the text section.
+	 * Optimally, this triggers a fault.
+	 * If not, we try calling the function after overwriting
+	 * to see if it returns the expected result as
+	 * confirmation that we truly executed the code we wrote.
+	 */
+	INFO("trying to write to text at %p\n", dst);
+	memcpy(dst, src, BUF_SIZE);
+	DO_BARRIERS();
+	i = overwrite_target(i);
+	if (i == 2) {
+		INFO("Overwrite of text succeeded!\n");
+	} else {
+		INFO("Did not get expected return value!\n");
+	}
+
+	zassert_unreachable("Write to text did not fault");
+}
+
+static void exec_data(void)
+{
+	execute_from_buffer(data_buf);
+	zassert_unreachable("Execute from data did not fault");
+}
+
+static void exec_stack(void)
+{
+	u8_t stack_buf[BUF_SIZE] __aligned(sizeof(int));
+
+	execute_from_buffer(stack_buf);
+	zassert_unreachable("Execute from stack did not fault");
+}
+
+#if (CONFIG_HEAP_MEM_POOL_SIZE > 0)
+static void exec_heap(void)
+{
+	u8_t *heap_buf = k_malloc(BUF_SIZE);
+
+	execute_from_buffer(heap_buf);
+	k_free(heap_buf);
+	zassert_unreachable("Execute from heap did not fault");
+}
+#endif
+
+void test_main(void *unused1, void *unused2, void *unused3)
+{
+	ztest_test_suite(test_protection,
+			 ztest_unit_test(write_ro),
+			 ztest_unit_test(write_text),
+			 ztest_unit_test(exec_data),
+			 ztest_unit_test(exec_stack)
+#if (CONFIG_HEAP_MEM_POOL_SIZE > 0)
+			 , ztest_unit_test(exec_heap)
+#endif
+		);
+	ztest_run_test_suite(test_protection);
+}

tests/kernel/protection/src/targets.c

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+#include <zephyr.h>
+#include <misc/printk.h>
+
+#include "targets.h"
+
+const u32_t rodata_var = RODATA_VALUE;
+
+u8_t data_buf[BUF_SIZE] __aligned(sizeof(int));
+
+int overwrite_target(int i)
+{
+	printk("text not modified\n");
+	return (i - 1);
+}

tests/kernel/protection/src/targets.h

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+#ifndef _PROT_TEST_TARGETS_H_
+#define _PROT_TEST_TARGETS_H_
+
+#define RODATA_VALUE  0xF00FF00F
+extern const u32_t rodata_var;
+
+#define BUF_SIZE 16
+extern u8_t data_buf[BUF_SIZE];
+
+extern int overwrite_target(int i);
+
+#endif

tests/kernel/protection/testcase.ini

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+[test]
+tags = core security ignore_faults
+filter = CONFIG_CPU_HAS_MPU or CONFIG_X86_MMU