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KeyStorage: improve logging for key generation

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The error messages that are printed when probing for rollback resistance
support on a device that doesn't support rollback-resistant keys can
make it sound like something is going wrong.  Print a WARNING message
afterwards to try to make it clear what is going on.  Also adjust or add
DEBUG messages when starting to generate each key so that it's easier to
distinguish the log messages for different key generation operations.

Bug: 182815123
Test: boot on device that doesn't support rollback-resistant keys and
      check log.
Change-Id: I37a13eb5c1e839fb94581f3e7ec1cd8da0263d2b
This commit is contained in:
Eric Biggers 2021-03-15 12:44:36 -07:00
parent 05bb5cc71e
commit b2024e0349
2 changed files with 25 additions and 17 deletions
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38
KeyStorage.cpp
View file

@ -133,17 +133,33 @@ static void hashWithPrefix(char const* prefix, const std::string& tohash, std::s
SHA512_Final(reinterpret_cast<uint8_t*>(&(*res)[0]), &c);
}
static bool generateKeymasterKey(Keymaster& keymaster, const KeyAuthentication& auth,
// Generates a keymaster key, using rollback resistance if supported.
static bool generateKeymasterKey(Keymaster& keymaster,
const km::AuthorizationSetBuilder& paramBuilder,
std::string* key) {
auto paramsWithRollback = paramBuilder;
paramsWithRollback.Authorization(km::TAG_ROLLBACK_RESISTANCE);
if (!keymaster.generateKey(paramsWithRollback, key)) {
LOG(WARNING) << "Failed to generate rollback-resistant key. This is expected if keymaster "
"doesn't support rollback resistance. Falling back to "
"non-rollback-resistant key.";
if (!keymaster.generateKey(paramBuilder, key)) return false;
}
return true;
}
static bool generateKeyStorageKey(Keymaster& keymaster, const KeyAuthentication& auth,
const std::string& appId, std::string* key) {
auto paramBuilder = km::AuthorizationSetBuilder()
.AesEncryptionKey(AES_KEY_BYTES * 8)
.GcmModeMinMacLen(GCM_MAC_BYTES * 8)
.Authorization(km::TAG_APPLICATION_ID, km::support::blob2hidlVec(appId));
if (auth.token.empty()) {
LOG(DEBUG) << "Creating key that doesn't need auth token";
LOG(DEBUG) << "Generating \"key storage\" key that doesn't need auth token";
paramBuilder.Authorization(km::TAG_NO_AUTH_REQUIRED);
} else {
LOG(DEBUG) << "Auth token required for key";
LOG(DEBUG) << "Generating \"key storage\" key that needs auth token";
if (auth.token.size() != sizeof(hw_auth_token_t)) {
LOG(ERROR) << "Auth token should be " << sizeof(hw_auth_token_t) << " bytes, was "
<< auth.token.size() << " bytes";
@ -155,13 +171,7 @@ static bool generateKeymasterKey(Keymaster& keymaster, const KeyAuthentication&
paramBuilder.Authorization(km::TAG_USER_AUTH_TYPE, km::HardwareAuthenticatorType::PASSWORD);
paramBuilder.Authorization(km::TAG_AUTH_TIMEOUT, AUTH_TIMEOUT);
}
auto paramsWithRollback = paramBuilder;
paramsWithRollback.Authorization(km::TAG_ROLLBACK_RESISTANCE);
// Generate rollback-resistant key if possible.
return keymaster.generateKey(paramsWithRollback, key) ||
keymaster.generateKey(paramBuilder, key);
return generateKeymasterKey(keymaster, paramBuilder, key);
}
bool generateWrappedStorageKey(KeyBuffer* key) {
@ -170,11 +180,7 @@ bool generateWrappedStorageKey(KeyBuffer* key) {
std::string key_temp;
auto paramBuilder = km::AuthorizationSetBuilder().AesEncryptionKey(AES_KEY_BYTES * 8);
paramBuilder.Authorization(km::TAG_STORAGE_KEY);
auto paramsWithRollback = paramBuilder;
paramsWithRollback.Authorization(km::TAG_ROLLBACK_RESISTANCE);
if (!keymaster.generateKey(paramsWithRollback, &key_temp)) {
if (!keymaster.generateKey(paramBuilder, &key_temp)) return false;
}
if (!generateKeymasterKey(keymaster, paramBuilder, &key_temp)) return false;
*key = KeyBuffer(key_temp.size());
memcpy(reinterpret_cast<void*>(key->data()), key_temp.c_str(), key->size());
return true;
@ -631,7 +637,7 @@ bool storeKey(const std::string& dir, const KeyAuthentication& auth, const KeyBu
Keymaster keymaster;
if (!keymaster) return false;
std::string kmKey;
if (!generateKeymasterKey(keymaster, auth, appId, &kmKey)) return false;
if (!generateKeyStorageKey(keymaster, auth, appId, &kmKey)) return false;
if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
km::AuthorizationSet keyParams;
km::HardwareAuthToken authToken;

2
KeyUtil.cpp
View file

@ -57,8 +57,10 @@ bool generateStorageKey(const KeyGeneration& gen, KeyBuffer* key) {
LOG(ERROR) << "Cannot generate a wrapped key " << gen.keysize << " bytes long";
return false;
}
LOG(DEBUG) << "Generating wrapped storage key";
return generateWrappedStorageKey(key);
} else {
LOG(DEBUG) << "Generating standard storage key";
return randomKey(gen.keysize, key);
}
}