tests: arch: arm mem protection check CPU scrubs regs after syscall

  at thread swap-in

- the mode variable (when building with support for either user

  space or FP shared registers) is saved and restored properly.

- the CPU registers are scrubbed after system call

Notes:

  The test verifies the correct behavior of the thread context-switch,

#if defined(CONFIG_USERSPACE)

#define PRIORITY 0

#define DB_VAL 0xDEADBEEF

static struct k_thread user_thread;

static K_THREAD_STACK_DEFINE(user_thread_stack, 1024);

		K_PRIO_COOP(PRIORITY), K_USER,

		K_NO_WAIT);

}

void z_impl_test_arm_cpu_write_reg(void)

{

	/* User thread CPU write registers system call for testing

	 *

	 * Verify the following

	 * - Write 0xDEADBEEF values during system call into registers

	 * - In main test we will read that registers to verify

	 * that all of them were scrubbed and do not contain any sensitive data

	 */

	/* Part below is made to test that kernel scrubs CPU registers

	 * after returning from the system call

	 */

	TC_PRINT("Writing 0xDEADBEEF values into registers\n");

	__asm__ volatile (

		"ldr r0, =0xDEADBEEF;\n\t"

		"ldr r1, =0xDEADBEEF;\n\t"

		"ldr r2, =0xDEADBEEF;\n\t"

		"ldr r3, =0xDEADBEEF;\n\t"

		);

	TC_PRINT("Exit from system call\n");

}

static inline void z_vrfy_test_arm_cpu_write_reg(void)

{

	z_impl_test_arm_cpu_write_reg();

}

#include <syscalls/test_arm_cpu_write_reg_mrsh.c>

/**

 * @brief Test CPU scrubs registers after system call

 *

 * @details - Call from user mode a syscall test_arm_cpu_write_reg(),

 * the system call function writes into registers 0xDEADBEEF value

 * - Then in main test function below check registers values,

 * if no 0xDEADBEEF value detected, that means CPU scrubbed registers

 * before exit from the system call.

 *

 * @ingroup kernel_memprotect_tests

 */

void test_syscall_cpu_scrubs_regs(void)

{

	uint32_t arm_reg_val[4];

	test_arm_cpu_write_reg();

	__asm__ volatile ("mov %0, r0" : "=r"(arm_reg_val[0]));

	__asm__ volatile ("mov %0, r1" : "=r"(arm_reg_val[1]));

	__asm__ volatile ("mov %0, r2" : "=r"(arm_reg_val[2]));

	__asm__ volatile ("mov %0, r3" : "=r"(arm_reg_val[3]));

	for (int i = 0; i < 4; i++) {

		zassert_not_equal(arm_reg_val[i], DB_VAL,

				"register value is 0xDEADBEEF, "

				"not scrubbed after system call.");

	}

}

#endif /* CONFIG_USERSPACE */

/**

 * @}

extern void test_arm_thread_swap(void);

extern void test_arm_syscalls(void);

extern void test_syscall_cpu_scrubs_regs(void);

void test_main(void)

{

	ztest_run_test_suite(arm_thread_swap);

#if defined(CONFIG_USERSPACE)

	ztest_test_suite(arm_syscalls,

		ztest_unit_test(test_arm_syscalls));

		ztest_unit_test(test_arm_syscalls),

		ztest_user_unit_test(test_syscall_cpu_scrubs_regs));

	ztest_run_test_suite(arm_syscalls);

#endif

}

#include <zephyr.h>

__syscall void test_arm_user_syscall(void);

__syscall void test_arm_cpu_write_reg(void);

#include <syscalls/test_syscalls.h>