fixup! bootutil: Add support for devices without erase and reduced er…

…ases

boot/bootutil/src/loader.c

@@ -1259,8 +1259,54 @@ int boot_scramble_region_backwards(const struct flash_area *fa, uint32_t off, ui
         return 0;
     }
 
+    if (flash_area_get_size(fa) < size || (flash_area_get_size(fa) - size) < off) {
+        return -EINVAL;
+    }
+
     if (device_requires_erase(fa)) {
-        return flash_area_erase(fa, off, size);
+        struct flash_sector sector;
+        uint32_t first_offset = 0;
+
+        /* Set boundary condition, the highest probable offset to erase, within
+         * last sector to erase
+         */
+        off += size - 1;
+
+        /* Get the lowest erased page offset first */
+        ret = flash_area_get_sector(fa, off, &sector);
+        if (ret < 0) {
+            return ret;
+        }
+        first_offset = flash_sector_get_off(&sector);
+
+        while (true) {
+            size_t cs;
+
+            /* Get current sector and, also, correct offset */
+            ret = flash_area_get_sector(fa, off, &sector);
+            if (ret < 0) {
+                return ret;
+            }
+
+            /* Corrected offset and size of current sector to erase */
+            off = flash_sector_get_off(&sector);
+            cs = flash_sector_get_size(&sector);
+
+            ret = flash_area_erase(fa, off, cs);
+            if (ret < 0) {
+                return ret;
+            }
+
+            if (first_offset == off) {
+                /* Reached the first offsset in range and already erased it */
+                break;
+            }
+
+            /* Move down to previous sector, the flash_area_get_sector will
+             * correct the value to real page offset
+             */
+            off -= 1;
+        }
     } else {
         uint8_t buf[BOOT_MAX_ALIGN];
         const size_t write_block = flash_area_align(fa);