efi_selftest: check executing in EL2

UEFI binaries should be executed in EL2 or EL1 even if U-Boot is started
in EL3. Provide a unit test.

Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

lib/efi_selftest/Makefile

@@ -51,6 +51,7 @@ efi_selftest_variables_runtime.o \
 efi_selftest_watchdog.o
 
 obj-$(CONFIG_EFI_ECPT) += efi_selftest_ecpt.o
+obj-$(CONFIG_ARM64) += efi_selftest_el.o
 obj-$(CONFIG_NETDEVICES) += efi_selftest_snp.o
 obj-$(CONFIG_EFI_HTTP_PROTOCOL) += efi_selftest_http.o
 obj-$(CONFIG_EFI_HTTP_PROTOCOL) += efi_selftest_ipconfig.o

lib/efi_selftest/efi_selftest_el.c

@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Check current exception level on ARMv8.
+ */
+#include <efi_loader.h>
+#include <efi_selftest.h>
+
+/**
+ * current_exception_level()
+ *
+ * Return:	current exception level, 0 - 3
+ */
+static unsigned int current_exception_level(void)
+{
+	unsigned long el;
+
+	asm volatile (
+		"MRS %0, CurrentEL"
+		: "=r" (el) : : );
+
+	return (el >> 2) & 0x3;
+}
+
+/**
+ * execute() - execute test
+ *
+ * Check that the exception level is not EL3.
+ */
+static int execute(void)
+{
+	unsigned int el = current_exception_level();
+
+	efi_st_printf("Exception level EL%u\n", el);
+	if (el != 1 && el != 2) {
+		efi_st_error("EL1 or EL2 expected");
+		return EFI_ST_FAILURE;
+	}
+
+	return EFI_ST_SUCCESS;
+}
+
+EFI_UNIT_TEST(el) = {
+	.name = "exception level",
+	.phase = EFI_EXECUTE_BEFORE_BOOTTIME_EXIT,
+	.execute = execute,
+};