esp8266/modesp: Add check_fw() function to check integrity of the firmware.

Requires firmware generated by the latest makeimg.py (which stores size
and md5 of the firmware together with the firmware itself).

esp8266/etshal.h

@@ -20,6 +20,13 @@ void ets_timer_arm_new(os_timer_t *tim, uint32_t millis, bool repeat, bool is_mi
 void ets_timer_setfn(os_timer_t *tim, ETSTimerFunc callback, void *cb_data);
 void ets_timer_disarm(os_timer_t *tim);
 
+// Opaque structure
+typedef char MD5_CTX[64];
+
+void MD5Init(MD5_CTX *context);
+void MD5Update(MD5_CTX *context, const void *data, unsigned int len);
+void MD5Final(unsigned char digest[16], MD5_CTX *context);
+
 // These prototypes are for recent SDKs with "malloc tracking"
 void *pvPortMalloc(unsigned sz, const char *fname, int line);
 void vPortFree(void *p, const char *fname, int line);

esp8266/modesp.c

@@ -633,6 +633,24 @@ STATIC mp_obj_t esp_flash_size(void) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_0(esp_flash_size_obj, esp_flash_size);
 
+STATIC mp_obj_t esp_check_fw(void) {
+    MD5_CTX ctx;
+    uint32_t *sz_p = (uint32_t*)0x40208ffc;
+    printf("size: %d\n", *sz_p);
+    MD5Init(&ctx);
+    MD5Update(&ctx, (char*)0x40200004, *sz_p - 4);
+    unsigned char digest[16];
+    MD5Final(digest, &ctx);
+    printf("md5: ");
+    for (int i = 0; i < 16; i++) {
+        printf("%02x", digest[i]);
+    }
+    printf("\n");
+    return mp_obj_new_bool(memcmp(digest, (void*)(0x40200000 + *sz_p), sizeof(digest)) == 0);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_0(esp_check_fw_obj, esp_check_fw);
+
+
 STATIC mp_obj_t esp_neopixel_write_(mp_obj_t pin, mp_obj_t buf, mp_obj_t is800k) {
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(buf, &bufinfo, MP_BUFFER_READ);
@@ -703,6 +721,7 @@ STATIC const mp_map_elem_t esp_module_globals_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR_dht_readinto), (mp_obj_t)&dht_readinto_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_freemem), (mp_obj_t)&esp_freemem_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_meminfo), (mp_obj_t)&esp_meminfo_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_check_fw), (mp_obj_t)&esp_check_fw_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_info), (mp_obj_t)&pyb_info_obj }, // TODO delete/rename/move elsewhere
     { MP_OBJ_NEW_QSTR(MP_QSTR_malloc), (mp_obj_t)&esp_malloc_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_free), (mp_obj_t)&esp_free_obj },