rboot: Add cryptographic digest support for OTA images & SHA256 example

examples/ota_basic/Makefile

@@ -1,5 +1,5 @@
 PROGRAM=ota_basic
 OTA=1
-EXTRA_COMPONENTS=extras/rboot-ota
+EXTRA_COMPONENTS=extras/rboot-ota extras/mbedtls
 include ../../common.mk
 

examples/ota_basic/ota_basic.c

@@ -6,12 +6,14 @@
  *
  * NOT SUITABLE TO PUT ON THE INTERNET OR INTO A PRODUCTION ENVIRONMENT!!!!
  */
+#include <string.h>
 #include "espressif/esp_common.h"
 #include "esp/uart.h"
 #include "FreeRTOS.h"
 #include "task.h"
 #include "esp8266.h"
 #include "ssid_config.h"
+#include "mbedtls/sha256.h"
 
 #include "ota-tftp.h"
 #include "rboot.h"
@@ -21,6 +23,9 @@
 #define TFTP_IMAGE_FILENAME1 "firmware1.bin"
 #define TFTP_IMAGE_FILENAME2 "firmware2.bin"
 
+/* Output of the command 'sha256sum firmware1.bin' */
+static const char *FIRMWARE1_SHA256 = "88199daff8b9e76975f685ec7f95bc1df3c61bd942a33a54a40707d2a41e5488";
+
 void tftp_client_task(void *pvParameters)
 {
     printf("TFTP client task starting...\n");
@@ -43,9 +48,43 @@ void tftp_client_task(void *pvParameters)
         int res = ota_tftp_download(TFTP_IMAGE_SERVER, TFTP_PORT, TFTP_IMAGE_FILENAME1, 1000, slot);
         printf("ota_tftp_download %s result %d\n", TFTP_IMAGE_FILENAME1, res);
         if(res == 0) {
-            printf("Rebooting into slot %d...\n", slot);
-            rboot_set_current_rom(slot);
-            sdk_system_restart();
+            printf("Looks valid, calculating SHA256...\n");
+            uint32_t length;
+            bool valid = rboot_verify_image(conf.roms[slot], &length, NULL);
+            static mbedtls_sha256_context ctx;
+            mbedtls_sha256_init(&ctx);
+            mbedtls_sha256_starts(&ctx, 0);
+            valid = valid && rboot_digest_image(conf.roms[slot], length, (rboot_digest_update_fn)mbedtls_sha256_update, &ctx);
+            static uint8_t hash_result[32];
+            mbedtls_sha256_finish(&ctx, hash_result);
+            mbedtls_sha256_free(&ctx);
+
+            if(!valid)
+            {
+                printf("Not valid after all :(\n");
+            }
+            else
+            {
+                printf("Image SHA256 = ");
+                bool valid = true;
+                for(int i = 0; i < sizeof(hash_result); i++) {
+                    char hexbuf[3];
+                    snprintf(hexbuf, 3, "%02x", hash_result[i]);
+                    printf(hexbuf);
+                    if(strncmp(hexbuf, FIRMWARE1_SHA256+i*2, 2))
+                        valid = false;
+
+                }
+                printf("\n");
+                if (valid) {
+                    printf("SHA256 Matches. Rebooting into slot %d...\n", slot);
+                    rboot_set_current_rom(slot);
+                    sdk_system_restart();
+                }
+                else {
+                    printf("Downloaded image SHA256 didn't match expected '%s'\n", FIRMWARE1_SHA256);
+                }
+            }
         }
         vTaskDelay(5000 / portTICK_RATE_MS);
 
@@ -77,5 +116,5 @@ void user_init(void)
     sdk_wifi_station_set_config(&config);
 
     ota_tftp_init_server(TFTP_PORT);
-    xTaskCreate(&tftp_client_task, (signed char *)"tftp_client", 1024, NULL, 2, NULL);
+    xTaskCreate(&tftp_client_task, (signed char *)"tftp_client", 2048, NULL, 2, NULL);
 }

extras/rboot-ota/ota-tftp.c

@@ -369,7 +369,9 @@ static err_t tftp_receive_data(struct netconn *nc, size_t write_offs, size_t lim
                it so the client gets an indication if things were successful.
             */
             const char *err = "Unknown validation error";
-            if(!rboot_verify_image(start_offs, *received_len, &err)) {
+            uint32_t image_length;
+            if(!rboot_verify_image(start_offs, &image_length, &err)
+               || image_length != *received_len) {
                 tftp_send_error(nc, TFTP_ERR_ILLEGAL, err);
                 return ERR_VAL;
             }

extras/rboot-ota/rboot-api.c

@@ -355,6 +355,20 @@ bool rboot_verify_image(uint32_t initial_offset, uint32_t *image_length, const c
     return false;
 }
 
+bool rboot_digest_image(uint32_t offset, uint32_t image_length, rboot_digest_update_fn update_fn, void *update_ctx)
+{
+    uint8_t buf[32] __attribute__((aligned(4)));
+    for(int i = 0; i < image_length; i += sizeof(buf)) {
+        if(sdk_spi_flash_read(offset+i, buf, sizeof(buf)))
+            return false;
+        uint32_t digest_len = sizeof(buf);
+        if(i + digest_len  > image_length)
+            digest_len = image_length - i;
+        update_fn(update_ctx, buf, digest_len);
+    }
+    return true;
+}
+
 #ifdef __cplusplus
 }
 #endif

extras/rboot-ota/rboot-api.h

@@ -144,6 +144,33 @@ uint32_t rboot_get_slot_offset(uint8_t slot);
 **/
 bool rboot_verify_image(uint32_t offset, uint32_t *image_length, const char **error_message);
 
+
+/* @description Digest callback prototype, designed to be compatible with
+   mbedtls digest functions (SHA, MD5, etc.)
+
+   See the ota_basic example to see an example of calculating the
+   SHA256 digest of an OTA image.
+*/
+typedef void (*rboot_digest_update_fn)(void * ctx, void *data, size_t data_len);
+
+/** @description Calculate a digest over the image at the offset specified
+
+    @note This function is actually a generic function that hashes SPI
+   flash contents, doesn't know anything about rboot image format. Use
+   rboot_verify_image to ensure a well-formed OTA image.
+
+   @param offset - Starting offset of image to hash (should be 4 byte aligned.)
+
+   @param image_length - Length of image to hash (should be 4 byte aligned.)
+
+   @param update_fn - Function to update digest (see rboot_digest_update_fn for details)
+
+   @param update_ctx - Context argument for digest update function.
+
+   @return True if digest completes successfully, false if digest function failed part way through
+**/
+bool rboot_digest_image(uint32_t offset, uint32_t image_length, rboot_digest_update_fn update_fn, void *update_ctx);
+
 #ifdef __cplusplus
 }
 #endif