Device.h

// Copyright (C) 2023, Mark Qvist

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

#include <Ed25519.h>

#if MCU_VARIANT == MCU_ESP32
#include "mbedtls/md.h"
#include "esp_ota_ops.h"
#include "esp_flash_partitions.h"
#include "esp_partition.h"

#elif MCU_VARIANT == MCU_NRF52
#include "Adafruit_nRFCrypto.h"

// size of chunk to retrieve from flash sector
#define CHUNK_SIZE 128

#define END_SECTION_SIZE 256

#if defined(NRF52840_XXAA)
// https://learn.adafruit.com/introducing-the-adafruit-nrf52840-feather/hathach-memory-map
// each section follows along from one another, in this order
// this is always at the start of the memory map
#define APPLICATION_START 0x26000

#define USER_DATA_START 0xED000
#endif

#endif

// Forward declaration from Utilities.h
void eeprom_update(int mapped_addr, uint8_t byte);
uint8_t eeprom_read(uint32_t addr);
void hard_reset(void);

#if !HAS_EEPROM && MCU_VARIANT == MCU_NRF52
  void eeprom_flush();
#endif

const uint8_t dev_keys [] PROGMEM = {
   0x0f, 0x15, 0x86, 0x74, 0xa0, 0x7d, 0xf2, 0xde, 0x32, 0x11, 0x29, 0xc1, 0x0d, 0xda, 0xcc, 0xc3,
   0xe1, 0x9b, 0xac, 0xf2, 0x27, 0x06, 0xee, 0x89, 0x1f, 0x7a, 0xfc, 0xc3, 0x6a, 0xf5, 0x38, 0x08
};

#define DEV_SIG_LEN 64
uint8_t dev_sig[DEV_SIG_LEN];

#define DEV_KEY_LEN 32
uint8_t dev_k_prv[DEV_KEY_LEN];
uint8_t dev_k_pub[DEV_KEY_LEN];

#define DEV_HASH_LEN 32
uint8_t dev_hash[DEV_HASH_LEN];
uint8_t dev_partition_table_hash[DEV_HASH_LEN];
uint8_t dev_bootloader_hash[DEV_HASH_LEN];
uint8_t dev_firmware_hash[DEV_HASH_LEN];
uint8_t dev_firmware_hash_target[DEV_HASH_LEN];

#define EEPROM_SIG_LEN 128
uint8_t dev_eeprom_signature[EEPROM_SIG_LEN];

bool dev_signature_validated = false;
bool fw_signature_validated = true;

#define DEV_SIG_OFFSET EEPROM_SIZE-EEPROM_RESERVED-DEV_SIG_LEN
#define dev_sig_addr(a) (a+DEV_SIG_OFFSET)

#define DEV_FWHASH_OFFSET EEPROM_SIZE-EEPROM_RESERVED-DEV_SIG_LEN-DEV_HASH_LEN
#define dev_fwhash_addr(a) (a+DEV_FWHASH_OFFSET)

bool device_signatures_ok() {
  return dev_signature_validated && fw_signature_validated;
}

void device_validate_signature() {
  int n_keys = sizeof(dev_keys)/DEV_KEY_LEN;
  bool valid_signature_found = false;
  for (int i = 0; i < n_keys; i++) {
    memcpy(dev_k_pub, dev_keys+DEV_KEY_LEN*i, DEV_KEY_LEN);
    if (Ed25519::verify(dev_sig, dev_k_pub, dev_hash, DEV_HASH_LEN)) {
        valid_signature_found = true;
    }
  }

  if (valid_signature_found) {
    dev_signature_validated = true;
  } else {
    dev_signature_validated = false;
  }
}

void device_save_signature() {
  device_validate_signature();
  if (dev_signature_validated) {
    for (uint8_t i = 0; i < DEV_SIG_LEN; i++) {
      eeprom_update(dev_sig_addr(i), dev_sig[i]);
    }
  }
}

void device_load_signature() {
  for (uint8_t i = 0; i < DEV_SIG_LEN; i++) {
    #if HAS_EEPROM
        dev_sig[i] = EEPROM.read(dev_sig_addr(i));
    #elif MCU_VARIANT == MCU_NRF52
        dev_sig[i] = eeprom_read(dev_sig_addr(i));
    #endif
  }
}

void device_load_firmware_hash() {
  for (uint8_t i = 0; i < DEV_HASH_LEN; i++) {
    #if HAS_EEPROM
        dev_firmware_hash_target[i] = EEPROM.read(dev_fwhash_addr(i));
    #elif MCU_VARIANT == MCU_NRF52
        dev_firmware_hash_target[i] = eeprom_read(dev_fwhash_addr(i));
    #endif
  }
}

void device_save_firmware_hash() {
  for (uint8_t i = 0; i < DEV_HASH_LEN; i++) {
    eeprom_update(dev_fwhash_addr(i), dev_firmware_hash_target[i]);
  }
  #if !HAS_EEPROM && MCU_VARIANT == MCU_NRF52
    eeprom_flush();
  #endif
  if (!fw_signature_validated) hard_reset();
}

#if MCU_VARIANT == MCU_NRF52
void calculate_region_hash(unsigned long long start, unsigned long long end, uint8_t* return_hash) {
    // this function calculates the hash digest of a region of memory,
    // currently it is only designed to work for the application region
    uint8_t chunk[CHUNK_SIZE] = {0};

    // to store potential last chunk of program
    uint8_t chunk_next[CHUNK_SIZE] = {0};
    nRFCrypto_Hash hash;

    hash.begin(CRYS_HASH_SHA256_mode);

    bool finish = false;
    uint8_t size;
    bool application = true;
    int end_count = 0;
    unsigned long length = 0;

    while (start < end - 1 ) {
        const void* src = (const void*)start;
        if (start + CHUNK_SIZE >= end) {
            size = (end - 1) - start;
        }
        else {
            size = CHUNK_SIZE;
        }

        memcpy(chunk, src, CHUNK_SIZE);

        // check if we've reached the end of the program
        // if we're checking the application region
        if (application) {
            for (int i = 0; i < CHUNK_SIZE; i++) {
                if (chunk[i] == 0xFF) {
                    bool matched = true;
                    end_count = 1;
                    // check if rest of chunk is FFs as well, only if FF is not
                    // at the end of chunk
                    if (i < CHUNK_SIZE - 1) {
                        for (int x = 0; x < CHUNK_SIZE - i; x++) {
                            if (chunk[i+x] != 0xFF) {
                                matched = false;
                                break;
                            }
                            end_count++;
                        }
                    }

                    if (matched) {
                        while (end_count < END_SECTION_SIZE) {
                            // check if bytes in next chunk up to total
                            // required are also FFs
                            for (int x = 1; x <= ceil(END_SECTION_SIZE / CHUNK_SIZE); x++) {
                                const void* src_next = (const void*)start + CHUNK_SIZE*x;
                                if ((END_SECTION_SIZE - end_count) > CHUNK_SIZE) {
                                    size = CHUNK_SIZE;
                                } else {
                                    size = END_SECTION_SIZE - end_count;
                                }
                                memcpy(chunk_next, src_next, size);
                                for (int y = 0; y < size; y++) {
                                    if (chunk_next[y] != 0xFF) {
                                        matched = false;
                                        break;
                                    }
                                    end_count++;
                                }

                                if (!matched) {
                                    break;
                                }
                            }
                            if (!matched) {
                                break;
                            }
                        }

                        if (matched) {
                            finish = true;
                            size = i;
                            break;
                        }
                    }
                }
            }
        }

        if (finish) {
            hash.update(chunk, size);
            length += size;
            break;
        } else {
            hash.update(chunk, size);
        }

        start += CHUNK_SIZE;
        length += CHUNK_SIZE;
    }
    hash.end(return_hash);
}
#endif

void device_validate_partitions() {
  device_load_firmware_hash();
  #if MCU_VARIANT == MCU_ESP32
  esp_partition_t partition;
  partition.address   = ESP_PARTITION_TABLE_OFFSET;
  partition.size      = ESP_PARTITION_TABLE_MAX_LEN;
  partition.type      = ESP_PARTITION_TYPE_DATA;
  esp_partition_get_sha256(&partition, dev_partition_table_hash);
  partition.address   = ESP_BOOTLOADER_OFFSET;
  partition.size      = ESP_PARTITION_TABLE_OFFSET;
  partition.type      = ESP_PARTITION_TYPE_APP;
  esp_partition_get_sha256(&partition, dev_bootloader_hash);
  esp_partition_get_sha256(esp_ota_get_running_partition(), dev_firmware_hash);
  #elif MCU_VARIANT == MCU_NRF52
  // todo, add bootloader, partition table, or softdevice?
  calculate_region_hash(APPLICATION_START, USER_DATA_START, dev_firmware_hash);
  #endif
    for (uint8_t i = 0; i < DEV_HASH_LEN; i++) {
      if (dev_firmware_hash_target[i] != dev_firmware_hash[i]) {
        fw_signature_validated = false;
        break;
      }
    }
}

bool device_firmware_ok() {
  return fw_signature_validated;
}

#if MCU_VARIANT == MCU_ESP32 || MCU_VARIANT == MCU_NRF52
bool device_init() {
  #if VALIDATE_FIRMWARE
  if (bt_ready) {
    #if MCU_VARIANT == MCU_ESP32
    for (uint8_t i=0; i<EEPROM_SIG_LEN; i++){dev_eeprom_signature[i]=EEPROM.read(eeprom_addr(ADDR_SIGNATURE+i));}
    mbedtls_md_context_t ctx;
    mbedtls_md_type_t md_type = MBEDTLS_MD_SHA256;     
    mbedtls_md_init(&ctx);
    mbedtls_md_setup(&ctx, mbedtls_md_info_from_type(md_type), 0);
    mbedtls_md_starts(&ctx);
    #if HAS_BLUETOOTH == true || HAS_BLE == true
      mbedtls_md_update(&ctx, dev_bt_mac, BT_DEV_ADDR_LEN);
    #else
      // TODO: Get from BLE stack instead
      // mbedtls_md_update(&ctx, dev_bt_mac, BT_DEV_ADDR_LEN);
    #endif
    mbedtls_md_update(&ctx, dev_eeprom_signature, EEPROM_SIG_LEN);
    mbedtls_md_finish(&ctx, dev_hash);
    mbedtls_md_free(&ctx);
    #elif MCU_VARIANT == MCU_NRF52
    for (uint8_t i=0; i<EEPROM_SIG_LEN; i++){dev_eeprom_signature[i]=eeprom_read(eeprom_addr(ADDR_SIGNATURE+i));}
    nRFCrypto.begin();

    nRFCrypto_Hash hash;

    hash.begin(CRYS_HASH_SHA256_mode);

    #if HAS_BLUETOOTH == true || HAS_BLE == true
      hash.update(dev_bt_mac, BT_DEV_ADDR_LEN);
    #else
      // TODO: Get from BLE stack instead
      // hash.update(dev_bt_mac, BT_DEV_ADDR_LEN);
    #endif
    hash.update(dev_eeprom_signature, EEPROM_SIG_LEN);

    hash.end(dev_hash);
    #endif

    device_load_signature();
    device_validate_signature();
    device_validate_partitions();

    #if MCU_VARIANT == MCU_NRF52
    nRFCrypto.end();
    #endif
    device_init_done = true;
    return device_init_done && fw_signature_validated;
  } else {
    return false;
  }
  #else
  // Skip hash comparison and checking BT
  device_init_done = true;
  return device_init_done;
  #endif
}
#endif