boot/zephyr: Support for loading images from arbitrary flash slots

Instead of normal MCUboot flow, that checks flash slots to find update
images, this patch enables an MCUboot application to chose from which
available slots to load an image.

This allows an application, for instance, to check hardware
configuration at runtime (by checking hardware straps, state of GPIOs,
etc) and decide from where to load an image to boot.

MCUboot will basically loop through provided image sources (flash slots)
and boot the first one that succed signature/validation. To provide the
image sources, the application need to provide strong implementation for
functions flash_map_id_get_next() and flash_map_id_get_current(). The
default, weak, implementations just keep current behaviour for single
loader, i.e. just load from FLASH_AREA_IMAGE_PRIMARY(0).

Note that in this case, MCUboot won't try to record if image succeeded
boot, it will only boot the image provided.

Signed-off-by: Ederson de Souza <ederson.desouza@intel.com>
Signed-off-by: Tom Burdick <thomas.burdick@intel.com>

Author: edersondisouza

boot/zephyr/Kconfig

@@ -383,6 +383,18 @@ config BOOT_IMAGE_EXECUTABLE_RAM_SIZE
 	default $(dt_chosen_reg_size_int,$(DT_CHOSEN_Z_SRAM),0)
 endif
 
+config FLASH_RUNTIME_SOURCES
+	bool "Images are read from flash partitions defined at runtime"
+	select SINGLE_APPLICATION_SLOT
+	help
+	  Instead of using information on the flash slots to decide which images
+	  to load/update, the application provides the information from which
+	  flash slot to load in runtime. This is useful when the application
+	  reads the state for hardware straps or other sources to decide which
+	  image to load. The application must provide `flash_map_id_get_next`
+	  and `flash_map_id_get_next` functions to tell mcuboot where to find
+	  the images.
+
 config BOOT_ENCRYPTION_SUPPORT
 	bool
 	help

boot/zephyr/flash_map_extended.c

@@ -58,6 +58,15 @@ int flash_device_base(uint8_t fd_id, uintptr_t *ret)
  */
 int flash_area_id_from_multi_image_slot(int image_index, int slot)
 {
+#if defined(CONFIG_FLASH_RUNTIME_SOURCES)
+    uint8_t id;
+
+    if (flash_map_id_get_current(&id)) {
+        return id;
+    }
+    return -1;
+#endif
+
     switch (slot) {
     case 0: return FLASH_AREA_IMAGE_PRIMARY(image_index);
 #if !defined(CONFIG_SINGLE_APPLICATION_SLOT)
@@ -141,7 +150,7 @@ int flash_area_sector_from_off(off_t off, struct flash_sector *sector)
 
 uint8_t flash_area_get_device_id(const struct flash_area *fa)
 {
-#if defined(CONFIG_ARM)
+#if defined(CONFIG_ARM) || defined(CONFIG_FLASH_RUNTIME_SOURCES)
     return fa->fa_id;
 #else
     (void)fa;

boot/zephyr/include/flash_runtime_sources.h

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2024 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef __FLASH_RUNTIME_SOURCES_H__
+#define __FLASH_RUNTIME_SOURCES_H__
+
+#include <inttypes.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * Get next flash map id.
+ *
+ * Implement this function to get the next flash map id. The function should
+ * return true if the flash map id was successfully updated. If the reset
+ * parameter is true, the function should reset the flash map id to the first
+ * one.
+ *
+ * @param id Pointer to the flash map id.
+ * @param reset If true, the function will reset the flash map id to the first
+ *             one.
+ * @retval true If the flash map id was successfully updated.
+ */
+bool flash_map_id_get_next(uint8_t *id, bool reset);
+
+/*
+ * Get current flash map id.
+ *
+ * Implement this function to get the current flash map id. The function should
+ * return true if the flash map id was successfully read.
+ *
+ * @param id Pointer to the flash map id.
+ * @retval true If the flash map id was successfully read.
+ */
+bool flash_map_id_get_current(uint8_t *id);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __FLASH_RUNTIME_SOURCES_H__ */

boot/zephyr/single_loader.c

@@ -20,6 +20,30 @@ BOOT_LOG_MODULE_DECLARE(mcuboot);
 static const struct flash_area *_fa_p;
 static struct image_header _hdr = { 0 };
 
+__weak bool
+flash_map_id_get_next(uint8_t *id, bool reset)
+{
+    if (!reset || !id) {
+        return false;
+    }
+
+    *id = FLASH_AREA_IMAGE_PRIMARY(0);
+
+    return true;
+}
+
+__weak bool
+flash_map_id_get_current(uint8_t *id)
+{
+    if (!id) {
+        return false;
+    }
+
+    *id = FLASH_AREA_IMAGE_PRIMARY(0);
+
+    return true;
+}
+
 #if defined(MCUBOOT_VALIDATE_PRIMARY_SLOT) || defined(MCUBOOT_VALIDATE_PRIMARY_SLOT_ONCE)
 /**
  * Validate hash of a primary boot image.
@@ -102,50 +126,65 @@ fih_ret
 boot_go(struct boot_rsp *rsp)
 {
     int rc = -1;
+    uint8_t flash_id;
+    bool reset = true;
     FIH_DECLARE(fih_rc, FIH_FAILURE);
 
-    rc = flash_area_open(FLASH_AREA_IMAGE_PRIMARY(0), &_fa_p);
-    assert(rc == 0);
+    while (flash_map_id_get_next(&flash_id, reset)) {
+        reset = false;
+        rc = flash_area_open(flash_id, &_fa_p);
+        if (rc != 0) {
+            continue;
+        }
 
-    rc = boot_image_load_header(_fa_p, &_hdr);
-    if (rc != 0)
-        goto out;
+        rc = boot_image_load_header(_fa_p, &_hdr);
+        if (rc != 0) {
+            flash_area_close(_fa_p);
+            continue;
+        }
 
 #ifdef MCUBOOT_RAM_LOAD
         static struct boot_loader_state state;
         state.imgs[0][0].hdr = _hdr;
 
         rc = boot_load_image_to_sram(&state);
-        if (rc != 0)
-            goto out;
+        if (rc != 0) {
+            flash_area_close(_fa_p);
+            continue;
+        }
 #endif
 
 #ifdef MCUBOOT_VALIDATE_PRIMARY_SLOT
-    FIH_CALL(boot_image_validate, fih_rc, _fa_p, &_hdr);
-    if (FIH_NOT_EQ(fih_rc, FIH_SUCCESS)) {
+        FIH_CALL(boot_image_validate, fih_rc, _fa_p, &_hdr);
+        if (FIH_NOT_EQ(fih_rc, FIH_SUCCESS)) {
+            flash_area_close(_fa_p);
 #ifdef MCUBOOT_RAM_LOAD
-        boot_remove_image_from_sram(&state);
+            boot_remove_image_from_sram(&state);
 #endif
-        goto out;
-    }
+            continue;
+        }
 #elif defined(MCUBOOT_VALIDATE_PRIMARY_SLOT_ONCE)
-    FIH_CALL(boot_image_validate_once, fih_rc, _fa_p, &_hdr);
-    if (FIH_NOT_EQ(fih_rc, FIH_SUCCESS)) {
+        FIH_CALL(boot_image_validate_once, fih_rc, _fa_p, &_hdr);
+        if (FIH_NOT_EQ(fih_rc, FIH_SUCCESS)) {
+            flash_area_close(_fa_p);
 #ifdef MCUBOOT_RAM_LOAD
-        boot_remove_image_from_sram(&state);
+            boot_remove_image_from_sram(&state);
 #endif
-        goto out;
-    }
+            continue;
+        }
 #else
-    fih_rc = FIH_SUCCESS;
+        fih_rc = FIH_SUCCESS;
 #endif /* MCUBOOT_VALIDATE_PRIMARY_SLOT */
 
-    rsp->br_flash_dev_id = flash_area_get_device_id(_fa_p);
-    rsp->br_image_off = flash_area_get_off(_fa_p);
-    rsp->br_hdr = &_hdr;
+        rsp->br_flash_dev_id = flash_area_get_device_id(_fa_p);
+        rsp->br_image_off = flash_area_get_off(_fa_p);
+        rsp->br_hdr = &_hdr;
+
+        flash_area_close(_fa_p);
+
+        break;
+    }
 
-out:
-    flash_area_close(_fa_p);
 
     FIH_RET(fih_rc);
 }