ARM: bootm: Allow booting in secure mode on hyp capable systems

Older Linux kernels will not properly boot in hyp mode, add support for a
bootm_boot_mode environment variable, which can be set to "sec" or "nonsec"
to force booting in secure or non-secure mode when build with non-sec support.

The default behavior can be selected through CONFIG_ARMV7_BOOT_SEC_DEFAULT,
when this is set booting in secure mode is the default. The default setting
for this Kconfig option is N, preserving the current behavior of booting in
non-secure mode by default when non-secure mode is supported.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>

arch/arm/cpu/armv7/Kconfig

@@ -13,6 +13,17 @@ config ARMV7_NONSEC
 	---help---
 	Say Y here to enable support for booting in non-secure / SVC mode.
 
+config ARMV7_BOOT_SEC_DEFAULT
+	boolean "Boot in secure mode by default" if EXPERT
+	depends on ARMV7_NONSEC
+	default n
+	---help---
+	Say Y here to boot in secure mode by default even if non-secure mode
+	is supported. This option is useful to boot kernels which do not
+	suppport booting in non-secure mode. Only set this if you need it.
+	This can be overriden at run-time by setting the bootm_boot_mode env.
+	variable to "sec" or "nonsec".
+
 config ARMV7_VIRT
 	boolean "Enable support for hardware virtualization" if EXPERT
 	depends on CPU_V7_HAS_VIRT && ARMV7_NONSEC

arch/arm/lib/bootm.c

@@ -237,6 +237,26 @@ static void boot_prep_linux(bootm_headers_t *images)
 	}
 }
 
+#if defined(CONFIG_ARMV7_NONSEC) || defined(CONFIG_ARMV7_VIRT)
+static bool boot_nonsec(void)
+{
+	char *s = getenv("bootm_boot_mode");
+#ifdef CONFIG_ARMV7_BOOT_SEC_DEFAULT
+	bool nonsec = false;
+#else
+	bool nonsec = true;
+#endif
+
+	if (s && !strcmp(s, "sec"))
+		nonsec = false;
+
+	if (s && !strcmp(s, "nonsec"))
+		nonsec = true;
+
+	return nonsec;
+}
+#endif
+
 /* Subcommand: GO */
 static void boot_jump_linux(bootm_headers_t *images, int flag)
 {
@@ -285,12 +305,13 @@ static void boot_jump_linux(bootm_headers_t *images, int flag)
 
 	if (!fake) {
 #if defined(CONFIG_ARMV7_NONSEC) || defined(CONFIG_ARMV7_VIRT)
+		if (boot_nonsec()) {
 			armv7_init_nonsec();
 			secure_ram_addr(_do_nonsec_entry)(kernel_entry,
 							  0, machid, r2);
-#else
+		} else
-		kernel_entry(0, machid, r2);
 #endif
+			kernel_entry(0, machid, r2);
 	}
 #endif
 }