loader: Add boot hook for slot selection

Add a bootloader hook to alter the logic of the active slot selection in
Direct XIP modes.

Signed-off-by: Tomasz Chyrowicz <[email protected]>

Author: tomchy

boot/bootutil/include/bootutil/boot_hooks.h

@@ -82,6 +82,18 @@
 
 #endif /* MCUBOOT_BOOT_GO_HOOKS  */
 
+#ifdef MCUBOOT_FIND_NEXT_SLOT_HOOKS
+
+#define BOOT_HOOK_FIND_SLOT_CALL(f, ret_default, ...) \
+    DO_HOOK_CALL(f, ret_default, __VA_ARGS__)
+
+#else
+
+#define BOOT_HOOK_FIND_SLOT_CALL(f, ret_default, ...) \
+    HOOK_CALL_NOP(f, ret_default, __VA_ARGS__)
+
+#endif /* MCUBOOT_FIND_NEXT_SLOT_HOOKS */
+
 #ifdef MCUBOOT_FLASH_AREA_HOOKS
 
 #define BOOT_HOOK_FLASH_AREA_CALL(f, ret_default, ...) \
@@ -260,4 +272,16 @@ int flash_area_get_device_id_hook(const struct flash_area *fa,
 #define BOOT_RESET_REQUEST_HOOK_CHECK_FAILED	3
 #define BOOT_RESET_REQUEST_HOOK_INTERNAL_ERROR	4
 
+/**
+ * Finds the preferred slot containing the image.
+ *
+ * @param[in]   state        Boot loader status information.
+ * @param[in]   image        Image, for which the slot should be found.
+ * @param[out]  active_slot  Number of the preferred slot.
+ *
+ * @return 0 if a slot was requested;
+ *         BOOT_HOOK_REGULAR follow the normal execution path.
+ */
+int boot_find_next_slot_hook(struct boot_loader_state *state, uint8_t image, uint32_t *active_slot);
+
 #endif /*H_BOOTUTIL_HOOKS*/

boot/bootutil/src/loader.c

@@ -2818,7 +2818,12 @@ boot_load_and_validate_images(struct boot_loader_state *state)
                 break;
             }
 
-            active_slot = find_slot_with_highest_version(state);
+            rc = BOOT_HOOK_FIND_SLOT_CALL(boot_find_next_slot_hook, BOOT_HOOK_REGULAR,
+                                          state, BOOT_CURR_IMG(state), &active_slot);
+            if (rc == BOOT_HOOK_REGULAR) {
+                active_slot = find_slot_with_highest_version(state);
+            }
+
             if (active_slot == NO_ACTIVE_SLOT) {
                 BOOT_LOG_INF("No slot to load for image %d",
                              BOOT_CURR_IMG(state));
@@ -2865,7 +2870,12 @@ boot_load_and_validate_images(struct boot_loader_state *state)
                 break;
             }
 
-            active_slot = find_slot_with_highest_version(state);
+            rc = BOOT_HOOK_FIND_SLOT_CALL(boot_find_next_slot_hook, BOOT_HOOK_REGULAR,
+                                          state, BOOT_CURR_IMG(state), &active_slot);
+            if (rc == BOOT_HOOK_REGULAR) {
+                active_slot = find_slot_with_highest_version(state);
+            }
+
             if (active_slot == NO_ACTIVE_SLOT) {
                 BOOT_LOG_INF("No slot to load for image %d",
                              BOOT_CURR_IMG(state));