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/*
* Copyright (C) 2016 The Android Open Source Project
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use, copy,
* modify, merge, publish, distribute, sublicense, and/or sell copies
* of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "avb_atx_validate.h"
#include <libavb/avb_rsa.h>
#include <libavb/avb_sha.h>
#include <libavb/avb_sysdeps.h>
#include <libavb/avb_util.h>
/* The most recent unlock challenge generated. */
static uint8_t last_unlock_challenge[AVB_ATX_UNLOCK_CHALLENGE_SIZE];
static bool last_unlock_challenge_set = false;
/* Computes the SHA256 |hash| of |length| bytes of |data|. */
static void sha256(const uint8_t* data,
uint32_t length,
uint8_t hash[AVB_SHA256_DIGEST_SIZE]) {
AvbSHA256Ctx context;
avb_sha256_init(&context);
avb_sha256_update(&context, data, length);
uint8_t* tmp = avb_sha256_final(&context);
avb_memcpy(hash, tmp, AVB_SHA256_DIGEST_SIZE);
}
/* Computes the SHA512 |hash| of |length| bytes of |data|. */
static void sha512(const uint8_t* data,
uint32_t length,
uint8_t hash[AVB_SHA512_DIGEST_SIZE]) {
AvbSHA512Ctx context;
avb_sha512_init(&context);
avb_sha512_update(&context, data, length);
uint8_t* tmp = avb_sha512_final(&context);
avb_memcpy(hash, tmp, AVB_SHA512_DIGEST_SIZE);
}
/* Computes the SHA256 |hash| of a NUL-terminated |str|. */
static void sha256_str(const char* str, uint8_t hash[AVB_SHA256_DIGEST_SIZE]) {
sha256((const uint8_t*)str, avb_strlen(str), hash);
}
/* Verifies structure and |expected_hash| of permanent |attributes|. */
static bool verify_permanent_attributes(
const AvbAtxPermanentAttributes* attributes,
const uint8_t expected_hash[AVB_SHA256_DIGEST_SIZE]) {
uint8_t hash[AVB_SHA256_DIGEST_SIZE];
if (attributes->version != 1) {
avb_error("Unsupported permanent attributes version.\n");
return false;
}
sha256((const uint8_t*)attributes, sizeof(AvbAtxPermanentAttributes), hash);
if (0 != avb_safe_memcmp(hash, expected_hash, AVB_SHA256_DIGEST_SIZE)) {
avb_error("Invalid permanent attributes.\n");
return false;
}
return true;
}
/* Verifies the format, key version, usage, and signature of a certificate. */
static bool verify_certificate(
const AvbAtxCertificate* certificate,
const uint8_t authority[AVB_ATX_PUBLIC_KEY_SIZE],
uint64_t minimum_key_version,
const uint8_t expected_usage[AVB_SHA256_DIGEST_SIZE]) {
const AvbAlgorithmData* algorithm_data;
uint8_t certificate_hash[AVB_SHA512_DIGEST_SIZE];
if (certificate->signed_data.version != 1) {
avb_error("Unsupported certificate format.\n");
return false;
}
algorithm_data = avb_get_algorithm_data(AVB_ALGORITHM_TYPE_SHA512_RSA4096);
sha512((const uint8_t*)&certificate->signed_data,
sizeof(AvbAtxCertificateSignedData),
certificate_hash);
if (!avb_rsa_verify(authority,
AVB_ATX_PUBLIC_KEY_SIZE,
certificate->signature,
AVB_RSA4096_NUM_BYTES,
certificate_hash,
AVB_SHA512_DIGEST_SIZE,
algorithm_data->padding,
algorithm_data->padding_len)) {
avb_error("Invalid certificate signature.\n");
return false;
}
if (certificate->signed_data.key_version < minimum_key_version) {
avb_error("Key rollback detected.\n");
return false;
}
if (0 != avb_safe_memcmp(certificate->signed_data.usage,
expected_usage,
AVB_SHA256_DIGEST_SIZE)) {
avb_error("Invalid certificate usage.\n");
return false;
}
return true;
}
/* Verifies signature and fields of a PIK certificate. */
static bool verify_pik_certificate(
const AvbAtxCertificate* certificate,
const uint8_t authority[AVB_ATX_PUBLIC_KEY_SIZE],
uint64_t minimum_version) {
uint8_t expected_usage[AVB_SHA256_DIGEST_SIZE];
sha256_str("com.google.android.things.vboot.ca", expected_usage);
if (!verify_certificate(
certificate, authority, minimum_version, expected_usage)) {
avb_error("Invalid PIK certificate.\n");
return false;
}
return true;
}
/* Verifies signature and fields of a PSK certificate. */
static bool verify_psk_certificate(
const AvbAtxCertificate* certificate,
const uint8_t authority[AVB_ATX_PUBLIC_KEY_SIZE],
uint64_t minimum_version,
const uint8_t product_id[AVB_ATX_PRODUCT_ID_SIZE]) {
uint8_t expected_subject[AVB_SHA256_DIGEST_SIZE];
uint8_t expected_usage[AVB_SHA256_DIGEST_SIZE];
sha256_str("com.google.android.things.vboot", expected_usage);
if (!verify_certificate(
certificate, authority, minimum_version, expected_usage)) {
avb_error("Invalid PSK certificate.\n");
return false;
}
sha256(product_id, AVB_ATX_PRODUCT_ID_SIZE, expected_subject);
if (0 != avb_safe_memcmp(certificate->signed_data.subject,
expected_subject,
AVB_SHA256_DIGEST_SIZE)) {
avb_error("PSK: Product ID mismatch.\n");
return false;
}
return true;
}
/* Verifies signature and fields of a PUK certificate. */
static bool verify_puk_certificate(
const AvbAtxCertificate* certificate,
const uint8_t authority[AVB_ATX_PUBLIC_KEY_SIZE],
uint64_t minimum_version,
const uint8_t product_id[AVB_ATX_PRODUCT_ID_SIZE]) {
uint8_t expected_subject[AVB_SHA256_DIGEST_SIZE];
uint8_t expected_usage[AVB_SHA256_DIGEST_SIZE];
sha256_str("com.google.android.things.vboot.unlock", expected_usage);
if (!verify_certificate(
certificate, authority, minimum_version, expected_usage)) {
avb_error("Invalid PUK certificate.\n");
return false;
}
sha256(product_id, AVB_ATX_PRODUCT_ID_SIZE, expected_subject);
if (0 != avb_safe_memcmp(certificate->signed_data.subject,
expected_subject,
AVB_SHA256_DIGEST_SIZE)) {
avb_error("PUK: Product ID mismatch.\n");
return false;
}
return true;
}
AvbIOResult avb_atx_validate_vbmeta_public_key(
AvbOps* ops,
const uint8_t* public_key_data,
size_t public_key_length,
const uint8_t* public_key_metadata,
size_t public_key_metadata_length,
bool* out_is_trusted) {
AvbIOResult result = AVB_IO_RESULT_OK;
AvbAtxPermanentAttributes permanent_attributes;
uint8_t permanent_attributes_hash[AVB_SHA256_DIGEST_SIZE];
AvbAtxPublicKeyMetadata metadata;
uint64_t minimum_version;
/* Be pessimistic so we can exit early without having to remember to clear.
*/
*out_is_trusted = false;
/* Read and verify permanent attributes. */
result = ops->atx_ops->read_permanent_attributes(ops->atx_ops,
&permanent_attributes);
if (result != AVB_IO_RESULT_OK) {
avb_error("Failed to read permanent attributes.\n");
return result;
}
result = ops->atx_ops->read_permanent_attributes_hash(
ops->atx_ops, permanent_attributes_hash);
if (result != AVB_IO_RESULT_OK) {
avb_error("Failed to read permanent attributes hash.\n");
return result;
}
if (!verify_permanent_attributes(&permanent_attributes,
permanent_attributes_hash)) {
return AVB_IO_RESULT_OK;
}
/* Sanity check public key metadata. */
if (public_key_metadata_length != sizeof(AvbAtxPublicKeyMetadata)) {
avb_error("Invalid public key metadata.\n");
return AVB_IO_RESULT_OK;
}
avb_memcpy(&metadata, public_key_metadata, sizeof(AvbAtxPublicKeyMetadata));
if (metadata.version != 1) {
avb_error("Unsupported public key metadata.\n");
return AVB_IO_RESULT_OK;
}
/* Verify the PIK certificate. */
result = ops->read_rollback_index(
ops, AVB_ATX_PIK_VERSION_LOCATION, &minimum_version);
if (result != AVB_IO_RESULT_OK) {
avb_error("Failed to read PIK minimum version.\n");
return result;
}
if (!verify_pik_certificate(&metadata.product_intermediate_key_certificate,
permanent_attributes.product_root_public_key,
minimum_version)) {
return AVB_IO_RESULT_OK;
}
/* Verify the PSK certificate. */
result = ops->read_rollback_index(
ops, AVB_ATX_PSK_VERSION_LOCATION, &minimum_version);
if (result != AVB_IO_RESULT_OK) {
avb_error("Failed to read PSK minimum version.\n");
return result;
}
if (!verify_psk_certificate(
&metadata.product_signing_key_certificate,
metadata.product_intermediate_key_certificate.signed_data.public_key,
minimum_version,
permanent_attributes.product_id)) {
return AVB_IO_RESULT_OK;
}
/* Verify the PSK is the same key that verified vbmeta. */
if (public_key_length != AVB_ATX_PUBLIC_KEY_SIZE) {
avb_error("Public key length mismatch.\n");
return AVB_IO_RESULT_OK;
}
if (0 != avb_safe_memcmp(
metadata.product_signing_key_certificate.signed_data.public_key,
public_key_data,
AVB_ATX_PUBLIC_KEY_SIZE)) {
avb_error("Public key mismatch.\n");
return AVB_IO_RESULT_OK;
}
/* Report the key versions used during verification. */
ops->atx_ops->set_key_version(
ops->atx_ops,
AVB_ATX_PIK_VERSION_LOCATION,
metadata.product_intermediate_key_certificate.signed_data.key_version);
ops->atx_ops->set_key_version(
ops->atx_ops,
AVB_ATX_PSK_VERSION_LOCATION,
metadata.product_signing_key_certificate.signed_data.key_version);
*out_is_trusted = true;
return AVB_IO_RESULT_OK;
}
AvbIOResult avb_atx_generate_unlock_challenge(
AvbAtxOps* atx_ops, AvbAtxUnlockChallenge* out_unlock_challenge) {
AvbIOResult result = AVB_IO_RESULT_OK;
AvbAtxPermanentAttributes permanent_attributes;
/* We need the permanent attributes to compute the product_id_hash. */
result = atx_ops->read_permanent_attributes(atx_ops, &permanent_attributes);
if (result != AVB_IO_RESULT_OK) {
avb_error("Failed to read permanent attributes.\n");
return result;
}
result = atx_ops->get_random(
atx_ops, AVB_ATX_UNLOCK_CHALLENGE_SIZE, last_unlock_challenge);
if (result != AVB_IO_RESULT_OK) {
avb_error("Failed to generate random challenge.\n");
return result;
}
last_unlock_challenge_set = true;
out_unlock_challenge->version = 1;
sha256(permanent_attributes.product_id,
AVB_ATX_PRODUCT_ID_SIZE,
out_unlock_challenge->product_id_hash);
avb_memcpy(out_unlock_challenge->challenge,
last_unlock_challenge,
AVB_ATX_UNLOCK_CHALLENGE_SIZE);
return result;
}
AvbIOResult avb_atx_validate_unlock_credential(
AvbAtxOps* atx_ops,
const AvbAtxUnlockCredential* unlock_credential,
bool* out_is_trusted) {
AvbIOResult result = AVB_IO_RESULT_OK;
AvbAtxPermanentAttributes permanent_attributes;
uint8_t permanent_attributes_hash[AVB_SHA256_DIGEST_SIZE];
uint64_t minimum_version;
const AvbAlgorithmData* algorithm_data;
uint8_t challenge_hash[AVB_SHA512_DIGEST_SIZE];
/* Be pessimistic so we can exit early without having to remember to clear.
*/
*out_is_trusted = false;
/* Sanity check the credential. */
if (unlock_credential->version != 1) {
avb_error("Unsupported unlock credential format.\n");
return AVB_IO_RESULT_OK;
}
/* Read and verify permanent attributes. */
result = atx_ops->read_permanent_attributes(atx_ops, &permanent_attributes);
if (result != AVB_IO_RESULT_OK) {
avb_error("Failed to read permanent attributes.\n");
return result;
}
result = atx_ops->read_permanent_attributes_hash(atx_ops,
permanent_attributes_hash);
if (result != AVB_IO_RESULT_OK) {
avb_error("Failed to read permanent attributes hash.\n");
return result;
}
if (!verify_permanent_attributes(&permanent_attributes,
permanent_attributes_hash)) {
return AVB_IO_RESULT_OK;
}
/* Verify the PIK certificate. */
result = atx_ops->ops->read_rollback_index(
atx_ops->ops, AVB_ATX_PIK_VERSION_LOCATION, &minimum_version);
if (result != AVB_IO_RESULT_OK) {
avb_error("Failed to read PIK minimum version.\n");
return result;
}
if (!verify_pik_certificate(
&unlock_credential->product_intermediate_key_certificate,
permanent_attributes.product_root_public_key,
minimum_version)) {
return AVB_IO_RESULT_OK;
}
/* Verify the PUK certificate. The minimum version is shared with the PSK. */
result = atx_ops->ops->read_rollback_index(
atx_ops->ops, AVB_ATX_PSK_VERSION_LOCATION, &minimum_version);
if (result != AVB_IO_RESULT_OK) {
avb_error("Failed to read PSK minimum version.\n");
return result;
}
if (!verify_puk_certificate(
&unlock_credential->product_unlock_key_certificate,
unlock_credential->product_intermediate_key_certificate.signed_data
.public_key,
minimum_version,
permanent_attributes.product_id)) {
return AVB_IO_RESULT_OK;
}
/* Hash the most recent unlock challenge. */
if (!last_unlock_challenge_set) {
avb_error("Challenge does not exist.\n");
return AVB_IO_RESULT_OK;
}
sha512(last_unlock_challenge, AVB_ATX_UNLOCK_CHALLENGE_SIZE, challenge_hash);
last_unlock_challenge_set = false;
/* Verify the challenge signature. */
algorithm_data = avb_get_algorithm_data(AVB_ALGORITHM_TYPE_SHA512_RSA4096);
if (!avb_rsa_verify(unlock_credential->product_unlock_key_certificate
.signed_data.public_key,
AVB_ATX_PUBLIC_KEY_SIZE,
unlock_credential->challenge_signature,
AVB_RSA4096_NUM_BYTES,
challenge_hash,
AVB_SHA512_DIGEST_SIZE,
algorithm_data->padding,
algorithm_data->padding_len)) {
avb_error("Invalid unlock challenge signature.\n");
return AVB_IO_RESULT_OK;
}
*out_is_trusted = true;
return AVB_IO_RESULT_OK;
}