trezor-firmware/legacy/fw_signatures.c

/*
 * This file is part of the Trezor project, https://trezor.io/
 *
 * Copyright (C) 2014 Pavol Rusnak <stick@satoshilabs.com>
 *
 * This library is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This library 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <string.h>

#include "ecdsa.h"
#include "fw_signatures.h"
#include "memory.h"
#include "memzero.h"
#include "secp256k1.h"
#include "sha2.h"

const uint32_t FIRMWARE_MAGIC_OLD = 0x525a5254;  // TRZR
const uint32_t FIRMWARE_MAGIC_NEW = 0x465a5254;  // TRZF

#define PUBKEYS 5

static const uint8_t * const pubkey[PUBKEYS] = {
        (const uint8_t *)"\x02\xd5\x71\xb7\xf1\x48\xc5\xe4\x23\x2c\x38\x14\xf7\x77\xd8\xfa\xea\xf1\xa8\x42\x16\xc7\x8d\x56\x9b\x71\x04\x1f\xfc\x76\x8a\x5b\x2d",
        (const uint8_t *)"\x03\x63\x27\x9c\x0c\x08\x66\xe5\x0c\x05\xc7\x99\xd3\x2b\xd6\xba\xb0\x18\x8b\x6d\xe0\x65\x36\xd1\x10\x9d\x2e\xd9\xce\x76\xcb\x33\x5c",
        (const uint8_t *)"\x02\x43\xae\xdb\xb6\xf7\xe7\x1c\x56\x3f\x8e\xd2\xef\x64\xec\x99\x81\x48\x25\x19\xe7\xef\x4f\x4a\xa9\x8b\x27\x85\x4e\x8c\x49\x12\x6d",
        (const uint8_t *)"\x02\x87\x7c\x39\xfd\x7c\x62\x23\x7e\x03\x82\x35\xe9\xc0\x75\xda\xb2\x61\x63\x0f\x78\xee\xb8\xed\xb9\x24\x87\x15\x9f\xff\xed\xfd\xf6",
        (const uint8_t *)"\x03\x73\x84\xc5\x1a\xe8\x1a\xdd\x0a\x52\x3a\xdb\xb1\x86\xc9\x1b\x90\x6f\xfb\x64\xc2\xc7\x65\x80\x2b\xf2\x6d\xbd\x13\xbd\xf1\x2c\x31"
};

#define SIGNATURES 3

#define FLASH_META_START 0x08008000
#define FLASH_META_CODELEN (FLASH_META_START + 0x0004)
#define FLASH_META_SIGINDEX1 (FLASH_META_START + 0x0008)
#define FLASH_META_SIGINDEX2 (FLASH_META_START + 0x0009)
#define FLASH_META_SIGINDEX3 (FLASH_META_START + 0x000A)
#define FLASH_OLD_APP_START 0x08010000
#define FLASH_META_SIG1 (FLASH_META_START + 0x0040)
#define FLASH_META_SIG2 (FLASH_META_START + 0x0080)
#define FLASH_META_SIG3 (FLASH_META_START + 0x00C0)

bool firmware_present_old(void) {
  if (memcmp(FLASH_PTR(FLASH_META_START), &FIRMWARE_MAGIC_OLD,
             4)) {  // magic does not match
    return false;
  }
  if (*((const uint32_t *)FLASH_PTR(FLASH_META_CODELEN)) <
      8192) {  // firmware reports smaller size than 8192
    return false;
  }
  if (*((const uint32_t *)FLASH_PTR(FLASH_META_CODELEN)) >
      FLASH_APP_LEN) {  // firmware reports bigger size than flash size
    return false;
  }

  return true;
}

int signatures_old_ok(void) {
  const uint32_t codelen = *((const uint32_t *)FLASH_META_CODELEN);
  const uint8_t sigindex1 = *((const uint8_t *)FLASH_META_SIGINDEX1);
  const uint8_t sigindex2 = *((const uint8_t *)FLASH_META_SIGINDEX2);
  const uint8_t sigindex3 = *((const uint8_t *)FLASH_META_SIGINDEX3);

  if (codelen > FLASH_APP_LEN) {
    return false;
  }

  uint8_t hash[32] = {0};
  sha256_Raw(FLASH_PTR(FLASH_OLD_APP_START), codelen, hash);

  if (sigindex1 < 1 || sigindex1 > PUBKEYS) return SIG_FAIL;  // invalid index
  if (sigindex2 < 1 || sigindex2 > PUBKEYS) return SIG_FAIL;  // invalid index
  if (sigindex3 < 1 || sigindex3 > PUBKEYS) return SIG_FAIL;  // invalid index

  if (sigindex1 == sigindex2) return SIG_FAIL;  // duplicate use
  if (sigindex1 == sigindex3) return SIG_FAIL;  // duplicate use
  if (sigindex2 == sigindex3) return SIG_FAIL;  // duplicate use

  if (0 != ecdsa_verify_digest(&secp256k1, pubkey[sigindex1 - 1],
                               (const uint8_t *)FLASH_META_SIG1,
                               hash)) {  // failure
    return SIG_FAIL;
  }
  if (0 != ecdsa_verify_digest(&secp256k1, pubkey[sigindex2 - 1],
                               (const uint8_t *)FLASH_META_SIG2,
                               hash)) {  // failure
    return SIG_FAIL;
  }
  if (0 != ecdsa_verify_digest(&secp256k1, pubkey[sigindex3 - 1],
                               (const uint8_t *)FLASH_META_SIG3,
                               hash)) {  // failure
    return SIG_FAIL;
  }

  return SIG_OK;
}

void compute_firmware_fingerprint(const image_header *hdr, uint8_t hash[32]) {
  image_header copy = {0};
  memcpy(&copy, hdr, sizeof(image_header));
  memzero(copy.sig1, sizeof(copy.sig1));
  memzero(copy.sig2, sizeof(copy.sig2));
  memzero(copy.sig3, sizeof(copy.sig3));
  copy.sigindex1 = 0;
  copy.sigindex2 = 0;
  copy.sigindex3 = 0;
  sha256_Raw((const uint8_t *)&copy, sizeof(image_header), hash);
}

bool firmware_present_new(void) {
  const image_header *hdr =
      (const image_header *)FLASH_PTR(FLASH_FWHEADER_START);
  if (hdr->magic != FIRMWARE_MAGIC_NEW) return false;
  // we need to ignore hdrlen for now
  // because we keep reset_handler ptr there
  // for compatibility with older bootloaders
  // after this is no longer necessary, let's uncomment the line below:
  // if (hdr->hdrlen != FLASH_FWHEADER_LEN) return false;
  if (hdr->codelen > FLASH_APP_LEN) return false;
  if (hdr->codelen < 4096) return false;

  return true;
}

int signatures_new_ok(const image_header *hdr, uint8_t store_fingerprint[32]) {
  uint8_t hash[32] = {0};
  compute_firmware_fingerprint(hdr, hash);

  if (store_fingerprint) {
    memcpy(store_fingerprint, hash, 32);
  }

  if (hdr->sigindex1 < 1 || hdr->sigindex1 > PUBKEYS)
    return SIG_FAIL;  // invalid index
  if (hdr->sigindex2 < 1 || hdr->sigindex2 > PUBKEYS)
    return SIG_FAIL;  // invalid index
  if (hdr->sigindex3 < 1 || hdr->sigindex3 > PUBKEYS)
    return SIG_FAIL;  // invalid index

  if (hdr->sigindex1 == hdr->sigindex2) return SIG_FAIL;  // duplicate use
  if (hdr->sigindex1 == hdr->sigindex3) return SIG_FAIL;  // duplicate use
  if (hdr->sigindex2 == hdr->sigindex3) return SIG_FAIL;  // duplicate use

  if (0 != ecdsa_verify_digest(&secp256k1, pubkey[hdr->sigindex1 - 1],
                               hdr->sig1, hash)) {  // failure
    return SIG_FAIL;
  }
  if (0 != ecdsa_verify_digest(&secp256k1, pubkey[hdr->sigindex2 - 1],
                               hdr->sig2, hash)) {  // failure
    return SIG_FAIL;
  }
  if (0 != ecdsa_verify_digest(&secp256k1, pubkey[hdr->sigindex3 - 1],
                               hdr->sig3, hash)) {  // failure
    return SIG_FAIL;
  }

  return SIG_OK;
}

int mem_is_empty(const uint8_t *src, uint32_t len) {
  for (uint32_t i = 0; i < len; i++) {
    if (src[i]) return 0;
  }
  return 1;
}

int check_firmware_hashes(const image_header *hdr) {
  uint8_t hash[32] = {0};
  // check hash of the first code chunk
  sha256_Raw(FLASH_PTR(FLASH_APP_START), (64 - 1) * 1024, hash);
  if (0 != memcmp(hash, hdr->hashes, 32)) return SIG_FAIL;
  // check remaining used chunks
  uint32_t total_len = FLASH_FWHEADER_LEN + hdr->codelen;
  int used_chunks = total_len / FW_CHUNK_SIZE;
  if (total_len % FW_CHUNK_SIZE > 0) {
    used_chunks++;
  }
  for (int i = 1; i < used_chunks; i++) {
    sha256_Raw(FLASH_PTR(FLASH_FWHEADER_START + (64 * i) * 1024), 64 * 1024,
               hash);
    if (0 != memcmp(hdr->hashes + 32 * i, hash, 32)) return SIG_FAIL;
  }
  // check unused chunks
  for (int i = used_chunks; i < 16; i++) {
    if (!mem_is_empty(hdr->hashes + 32 * i, 32)) return SIG_FAIL;
  }
  // all OK
  return SIG_OK;
}