[PATCH RFC 13/17] bootm: make unsigned image support runtime configurable

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

To allow runtime unlocking of a device via security policies, add a new
SCONFIG_BOOT_UNSIGNED_IMAGES option and consult it.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 common/Sconfig | 15 +++++++++++++++
 common/bootm.c | 26 +++++++++++++++++++++++++-
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/common/Sconfig b/common/Sconfig
index 479ac5cdf2e5..edbc4bc028af 100644
--- a/common/Sconfig
+++ b/common/Sconfig
@@ -7,3 +7,18 @@ config RATP
 	depends on $(kconfig-enabled,CONSOLE_RATP)
 
 endmenu
+
+menu "Boot Policy"
+
+config BOOT_UNSIGNED_IMAGES
+	bool "Allow booting unsigned images"
+	depends on $(kconfig-enabled,BOOTM_OPTIONAL_SIGNED_IMAGES)
+	help
+	  Say y here if you want to allow booting of images with
+	  an invalid signature or no signature at all.
+
+	  Systems with verified boot chains should say y here
+	  or force it at compile time irrespective of policy
+	  with CONFIG_BOOTM_FORCE_SIGNED_IMAGES
+
+endmenu
diff --git a/common/bootm.c b/common/bootm.c
index 5c129cd4b579..c417e760595a 100644
--- a/common/bootm.c
+++ b/common/bootm.c
@@ -16,8 +16,10 @@
 #include <magicvar.h>
 #include <uncompress.h>
 #include <zero_page.h>
+#include <security/config.h>
 
 static LIST_HEAD(handler_list);
+static struct sconfig_notifier_block sconfig_notifier;
 
 static __maybe_unused struct bootm_overrides bootm_overrides;
 
@@ -114,6 +116,13 @@ static const char * const bootm_verify_names[] = {
 	[BOOTM_VERIFY_SIGNATURE] = "signature",
 };
 
+/*
+ * There's three ways to influence whether signed images are forced:
+ * 1) CONFIG_BOOTM_FORCE_SIGNED_IMAGES: forced at compile time
+ * 2) SCONFIG_BOOT_UNSIGNED_IMAGES: determined by the active security policy
+ * 3) bootm_force_signed_images(): forced dynamically by board code.
+ *                                 will be deprecated in favor of 2)
+ */
 static bool force_signed_images = IS_ENABLED(CONFIG_BOOTM_FORCE_SIGNED_IMAGES);
 
 static void bootm_optional_signed_images(void)
@@ -141,6 +150,16 @@ static void bootm_require_signed_images(void)
 	bootm_verify_mode = BOOTM_VERIFY_SIGNATURE;
 }
 
+static void bootm_unsigned_sconfig_update(struct sconfig_notifier_block *nb,
+					  enum security_config_option opt,
+					  bool allowed)
+{
+	if (!allowed)
+		bootm_require_signed_images();
+	else
+		bootm_optional_signed_images();
+}
+
 void bootm_force_signed_images(void)
 {
 	bootm_require_signed_images();
@@ -149,7 +168,7 @@ void bootm_force_signed_images(void)
 
 bool bootm_signed_images_are_forced(void)
 {
-	return force_signed_images;
+	return force_signed_images || !IS_ALLOWED(SCONFIG_BOOT_UNSIGNED_IMAGES);
 }
 
 static int uimage_part_num(const char *partname)
@@ -1098,6 +1117,11 @@ static int bootm_init(void)
 	else
 		bootm_optional_signed_images();
 
+	sconfig_register_handler_filtered(&sconfig_notifier,
+					  bootm_unsigned_sconfig_update,
+					  SCONFIG_BOOT_UNSIGNED_IMAGES);
+
+
 	if (IS_ENABLED(CONFIG_ROOTWAIT_BOOTARG))
 		globalvar_add_simple_int("linux.rootwait",
 					 &linux_rootwait_secs, "%d");
-- 
2.39.5