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platform_system_vold/KeyStorage.cpp
Shawn Willden f452774030 Break vold dependency on keystore utilities. 
This is temporary.  Keystore is in the process of being upgraded to use
the new Keymaster 4.0 HAL, and I want to leave vold alone, using
Keymaster 3.0 for the moment.  This CL just copies relevant bits of
keystore support utilities into vold, so it can stop depending on the
copies from keystore.

After the keystore update is complete, vold will be changed either to
use Keymaster 4.0 or -- more likely -- to use keystore rather than
talking to Keymaster directly.  At that point the files added by this CL
will be deleted.

Test: Device boots and successfully decrypts /data
Change-Id: I73f6d4cc4c5e20d89d7ac37d29d025bf279f9e12
2017-11-09 16:05:38 -07:00

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/*
* Copyright (C) 2016 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "KeyStorage.h"
#include "Keymaster.h"
#include "ScryptParameters.h"
#include "Utils.h"
#include <vector>
#include <errno.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/sha.h>
#include <android-base/file.h>
#include <android-base/logging.h>
#include <cutils/properties.h>
#include <hardware/hw_auth_token.h>
extern "C" {
#include "crypto_scrypt.h"
}
#include "authorization_set.h"
#include "keystore_hidl_support.h"
namespace android {
namespace vold {
using namespace keystore;
const KeyAuthentication kEmptyAuthentication{"", ""};
static constexpr size_t AES_KEY_BYTES = 32;
static constexpr size_t GCM_NONCE_BYTES = 12;
static constexpr size_t GCM_MAC_BYTES = 16;
static constexpr size_t SALT_BYTES = 1 << 4;
static constexpr size_t SECDISCARDABLE_BYTES = 1 << 14;
static constexpr size_t STRETCHED_BYTES = 1 << 6;
static constexpr uint32_t AUTH_TIMEOUT = 30; // Seconds
static const char* kCurrentVersion = "1";
static const char* kRmPath = "/system/bin/rm";
static const char* kSecdiscardPath = "/system/bin/secdiscard";
static const char* kStretch_none = "none";
static const char* kStretch_nopassword = "nopassword";
static const std::string kStretchPrefix_scrypt = "scrypt ";
static const char* kHashPrefix_secdiscardable = "Android secdiscardable SHA512";
static const char* kHashPrefix_keygen = "Android key wrapping key generation SHA512";
static const char* kFn_encrypted_key = "encrypted_key";
static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
static const char* kFn_keymaster_key_blob_upgraded = "keymaster_key_blob_upgraded";
static const char* kFn_salt = "salt";
static const char* kFn_secdiscardable = "secdiscardable";
static const char* kFn_stretching = "stretching";
static const char* kFn_version = "version";
static bool checkSize(const std::string& kind, size_t actual, size_t expected) {
if (actual != expected) {
LOG(ERROR) << "Wrong number of bytes in " << kind << ", expected " << expected << " got "
<< actual;
return false;
}
return true;
}
static void hashWithPrefix(char const* prefix, const std::string& tohash, std::string* res) {
SHA512_CTX c;
SHA512_Init(&c);
// Personalise the hashing by introducing a fixed prefix.
// Hashing applications should use personalization except when there is a
// specific reason not to; see section 4.11 of https://www.schneier.com/skein1.3.pdf
std::string hashingPrefix = prefix;
hashingPrefix.resize(SHA512_CBLOCK);
SHA512_Update(&c, hashingPrefix.data(), hashingPrefix.size());
SHA512_Update(&c, tohash.data(), tohash.size());
res->assign(SHA512_DIGEST_LENGTH, '\0');
SHA512_Final(reinterpret_cast<uint8_t*>(&(*res)[0]), &c);
}
static bool generateKeymasterKey(Keymaster& keymaster, const KeyAuthentication& auth,
const std::string& appId, std::string* key) {
auto paramBuilder = AuthorizationSetBuilder()
.AesEncryptionKey(AES_KEY_BYTES * 8)
.Authorization(TAG_BLOCK_MODE, BlockMode::GCM)
.Authorization(TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
.Authorization(TAG_PADDING, PaddingMode::NONE)
.Authorization(TAG_APPLICATION_ID, blob2hidlVec(appId));
if (auth.token.empty()) {
LOG(DEBUG) << "Creating key that doesn't need auth token";
paramBuilder.Authorization(TAG_NO_AUTH_REQUIRED);
} else {
LOG(DEBUG) << "Auth token required for key";
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";
return false;
}
const hw_auth_token_t* at = reinterpret_cast<const hw_auth_token_t*>(auth.token.data());
paramBuilder.Authorization(TAG_USER_SECURE_ID, at->user_id);
paramBuilder.Authorization(TAG_USER_AUTH_TYPE, HardwareAuthenticatorType::PASSWORD);
paramBuilder.Authorization(TAG_AUTH_TIMEOUT, AUTH_TIMEOUT);
}
return keymaster.generateKey(paramBuilder, key);
}
static AuthorizationSet beginParams(const KeyAuthentication& auth,
const std::string& appId) {
auto paramBuilder = AuthorizationSetBuilder()
.Authorization(TAG_BLOCK_MODE, BlockMode::GCM)
.Authorization(TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
.Authorization(TAG_PADDING, PaddingMode::NONE)
.Authorization(TAG_APPLICATION_ID, blob2hidlVec(appId));
if (!auth.token.empty()) {
LOG(DEBUG) << "Supplying auth token to Keymaster";
paramBuilder.Authorization(TAG_AUTH_TOKEN, blob2hidlVec(auth.token));
}
return paramBuilder;
}
static bool readFileToString(const std::string& filename, std::string* result) {
if (!android::base::ReadFileToString(filename, result)) {
PLOG(ERROR) << "Failed to read from " << filename;
return false;
}
return true;
}
static bool writeStringToFile(const std::string& payload, const std::string& filename) {
if (!android::base::WriteStringToFile(payload, filename)) {
PLOG(ERROR) << "Failed to write to " << filename;
return false;
}
return true;
}
static bool readRandomBytesOrLog(size_t count, std::string* out) {
auto status = ReadRandomBytes(count, *out);
if (status != OK) {
LOG(ERROR) << "Random read failed with status: " << status;
return false;
}
return true;
}
bool createSecdiscardable(const std::string& filename, std::string* hash) {
std::string secdiscardable;
if (!readRandomBytesOrLog(SECDISCARDABLE_BYTES, &secdiscardable)) return false;
if (!writeStringToFile(secdiscardable, filename)) return false;
hashWithPrefix(kHashPrefix_secdiscardable, secdiscardable, hash);
return true;
}
bool readSecdiscardable(const std::string& filename, std::string* hash) {
std::string secdiscardable;
if (!readFileToString(filename, &secdiscardable)) return false;
hashWithPrefix(kHashPrefix_secdiscardable, secdiscardable, hash);
return true;
}
static KeymasterOperation begin(Keymaster& keymaster, const std::string& dir,
KeyPurpose purpose,
const AuthorizationSet &keyParams,
const AuthorizationSet &opParams,
AuthorizationSet* outParams) {
auto kmKeyPath = dir + "/" + kFn_keymaster_key_blob;
std::string kmKey;
if (!readFileToString(kmKeyPath, &kmKey)) return KeymasterOperation();
AuthorizationSet inParams(keyParams);
inParams.append(opParams.begin(), opParams.end());
for (;;) {
auto opHandle = keymaster.begin(purpose, kmKey, inParams, outParams);
if (opHandle) {
return opHandle;
}
if (opHandle.errorCode() != ErrorCode::KEY_REQUIRES_UPGRADE) return opHandle;
LOG(DEBUG) << "Upgrading key: " << dir;
std::string newKey;
if (!keymaster.upgradeKey(kmKey, keyParams, &newKey)) return KeymasterOperation();
auto newKeyPath = dir + "/" + kFn_keymaster_key_blob_upgraded;
if (!writeStringToFile(newKey, newKeyPath)) return KeymasterOperation();
if (rename(newKeyPath.c_str(), kmKeyPath.c_str()) != 0) {
PLOG(ERROR) << "Unable to move upgraded key to location: " << kmKeyPath;
return KeymasterOperation();
}
if (!keymaster.deleteKey(kmKey)) {
LOG(ERROR) << "Key deletion failed during upgrade, continuing anyway: " << dir;
}
kmKey = newKey;
LOG(INFO) << "Key upgraded: " << dir;
}
}
static bool encryptWithKeymasterKey(Keymaster& keymaster, const std::string& dir,
const AuthorizationSet &keyParams,
const KeyBuffer& message, std::string* ciphertext) {
AuthorizationSet opParams;
AuthorizationSet outParams;
auto opHandle = begin(keymaster, dir, KeyPurpose::ENCRYPT, keyParams, opParams, &outParams);
if (!opHandle) return false;
auto nonceBlob = outParams.GetTagValue(TAG_NONCE);
if (!nonceBlob.isOk()) {
LOG(ERROR) << "GCM encryption but no nonce generated";
return false;
}
// nonceBlob here is just a pointer into existing data, must not be freed
std::string nonce(reinterpret_cast<const char*>(&nonceBlob.value()[0]), nonceBlob.value().size());
if (!checkSize("nonce", nonce.size(), GCM_NONCE_BYTES)) return false;
std::string body;
if (!opHandle.updateCompletely(message, &body)) return false;
std::string mac;
if (!opHandle.finish(&mac)) return false;
if (!checkSize("mac", mac.size(), GCM_MAC_BYTES)) return false;
*ciphertext = nonce + body + mac;
return true;
}
static bool decryptWithKeymasterKey(Keymaster& keymaster, const std::string& dir,
const AuthorizationSet &keyParams,
const std::string& ciphertext, KeyBuffer* message) {
auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
auto opParams = AuthorizationSetBuilder()
.Authorization(TAG_NONCE, blob2hidlVec(nonce));
auto opHandle = begin(keymaster, dir, KeyPurpose::DECRYPT, keyParams, opParams, nullptr);
if (!opHandle) return false;
if (!opHandle.updateCompletely(bodyAndMac, message)) return false;
if (!opHandle.finish(nullptr)) return false;
return true;
}
static std::string getStretching(const KeyAuthentication& auth) {
if (!auth.usesKeymaster()) {
return kStretch_none;
} else if (auth.secret.empty()) {
return kStretch_nopassword;
} else {
char paramstr[PROPERTY_VALUE_MAX];
property_get(SCRYPT_PROP, paramstr, SCRYPT_DEFAULTS);
return std::string() + kStretchPrefix_scrypt + paramstr;
}
}
static bool stretchingNeedsSalt(const std::string& stretching) {
return stretching != kStretch_nopassword && stretching != kStretch_none;
}
static bool stretchSecret(const std::string& stretching, const std::string& secret,
const std::string& salt, std::string* stretched) {
if (stretching == kStretch_nopassword) {
if (!secret.empty()) {
LOG(WARNING) << "Password present but stretching is nopassword";
// Continue anyway
}
stretched->clear();
} else if (stretching == kStretch_none) {
*stretched = secret;
} else if (std::equal(kStretchPrefix_scrypt.begin(), kStretchPrefix_scrypt.end(),
stretching.begin())) {
int Nf, rf, pf;
if (!parse_scrypt_parameters(stretching.substr(kStretchPrefix_scrypt.size()).c_str(), &Nf,
&rf, &pf)) {
LOG(ERROR) << "Unable to parse scrypt params in stretching: " << stretching;
return false;
}
stretched->assign(STRETCHED_BYTES, '\0');
if (crypto_scrypt(reinterpret_cast<const uint8_t*>(secret.data()), secret.size(),
reinterpret_cast<const uint8_t*>(salt.data()), salt.size(),
1 << Nf, 1 << rf, 1 << pf,
reinterpret_cast<uint8_t*>(&(*stretched)[0]), stretched->size()) != 0) {
LOG(ERROR) << "scrypt failed with params: " << stretching;
return false;
}
} else {
LOG(ERROR) << "Unknown stretching type: " << stretching;
return false;
}
return true;
}
static bool generateAppId(const KeyAuthentication& auth, const std::string& stretching,
const std::string& salt, const std::string& secdiscardable_hash,
std::string* appId) {
std::string stretched;
if (!stretchSecret(stretching, auth.secret, salt, &stretched)) return false;
*appId = secdiscardable_hash + stretched;
return true;
}
static void logOpensslError() {
LOG(ERROR) << "Openssl error: " << ERR_get_error();
}
static bool encryptWithoutKeymaster(const std::string& preKey,
const KeyBuffer& plaintext, std::string* ciphertext) {
std::string key;
hashWithPrefix(kHashPrefix_keygen, preKey, &key);
key.resize(AES_KEY_BYTES);
if (!readRandomBytesOrLog(GCM_NONCE_BYTES, ciphertext)) return false;
auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free);
if (!ctx) {
logOpensslError();
return false;
}
if (1 != EVP_EncryptInit_ex(ctx.get(), EVP_aes_256_gcm(), NULL,
reinterpret_cast<const uint8_t*>(key.data()),
reinterpret_cast<const uint8_t*>(ciphertext->data()))) {
logOpensslError();
return false;
}
ciphertext->resize(GCM_NONCE_BYTES + plaintext.size() + GCM_MAC_BYTES);
int outlen;
if (1 != EVP_EncryptUpdate(ctx.get(),
reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES), &outlen,
reinterpret_cast<const uint8_t*>(plaintext.data()), plaintext.size())) {
logOpensslError();
return false;
}
if (outlen != static_cast<int>(plaintext.size())) {
LOG(ERROR) << "GCM ciphertext length should be " << plaintext.size() << " was " << outlen;
return false;
}
if (1 != EVP_EncryptFinal_ex(ctx.get(),
reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()), &outlen)) {
logOpensslError();
return false;
}
if (outlen != 0) {
LOG(ERROR) << "GCM EncryptFinal should be 0, was " << outlen;
return false;
}
if (1 != EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_GET_TAG, GCM_MAC_BYTES,
reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()))) {
logOpensslError();
return false;
}
return true;
}
static bool decryptWithoutKeymaster(const std::string& preKey,
const std::string& ciphertext, KeyBuffer* plaintext) {
if (ciphertext.size() < GCM_NONCE_BYTES + GCM_MAC_BYTES) {
LOG(ERROR) << "GCM ciphertext too small: " << ciphertext.size();
return false;
}
std::string key;
hashWithPrefix(kHashPrefix_keygen, preKey, &key);
key.resize(AES_KEY_BYTES);
auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free);
if (!ctx) {
logOpensslError();
return false;
}
if (1 != EVP_DecryptInit_ex(ctx.get(), EVP_aes_256_gcm(), NULL,
reinterpret_cast<const uint8_t*>(key.data()),
reinterpret_cast<const uint8_t*>(ciphertext.data()))) {
logOpensslError();
return false;
}
*plaintext = KeyBuffer(ciphertext.size() - GCM_NONCE_BYTES - GCM_MAC_BYTES);
int outlen;
if (1 != EVP_DecryptUpdate(ctx.get(),
reinterpret_cast<uint8_t*>(&(*plaintext)[0]), &outlen,
reinterpret_cast<const uint8_t*>(ciphertext.data() + GCM_NONCE_BYTES), plaintext->size())) {
logOpensslError();
return false;
}
if (outlen != static_cast<int>(plaintext->size())) {
LOG(ERROR) << "GCM plaintext length should be " << plaintext->size() << " was " << outlen;
return false;
}
if (1 != EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_SET_TAG, GCM_MAC_BYTES,
const_cast<void *>(
reinterpret_cast<const void*>(ciphertext.data() + GCM_NONCE_BYTES + plaintext->size())))) {
logOpensslError();
return false;
}
if (1 != EVP_DecryptFinal_ex(ctx.get(),
reinterpret_cast<uint8_t*>(&(*plaintext)[0] + plaintext->size()), &outlen)) {
logOpensslError();
return false;
}
if (outlen != 0) {
LOG(ERROR) << "GCM EncryptFinal should be 0, was " << outlen;
return false;
}
return true;
}
bool pathExists(const std::string& path) {
return access(path.c_str(), F_OK) == 0;
}
bool storeKey(const std::string& dir, const KeyAuthentication& auth, const KeyBuffer& key) {
if (TEMP_FAILURE_RETRY(mkdir(dir.c_str(), 0700)) == -1) {
PLOG(ERROR) << "key mkdir " << dir;
return false;
}
if (!writeStringToFile(kCurrentVersion, dir + "/" + kFn_version)) return false;
std::string secdiscardable_hash;
if (!createSecdiscardable(dir + "/" + kFn_secdiscardable, &secdiscardable_hash)) return false;
std::string stretching = getStretching(auth);
if (!writeStringToFile(stretching, dir + "/" + kFn_stretching)) return false;
std::string salt;
if (stretchingNeedsSalt(stretching)) {
if (ReadRandomBytes(SALT_BYTES, salt) != OK) {
LOG(ERROR) << "Random read failed";
return false;
}
if (!writeStringToFile(salt, dir + "/" + kFn_salt)) return false;
}
std::string appId;
if (!generateAppId(auth, stretching, salt, secdiscardable_hash, &appId)) return false;
std::string encryptedKey;
if (auth.usesKeymaster()) {
Keymaster keymaster;
if (!keymaster) return false;
std::string kmKey;
if (!generateKeymasterKey(keymaster, auth, appId, &kmKey)) return false;
if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
auto keyParams = beginParams(auth, appId);
if (!encryptWithKeymasterKey(keymaster, dir, keyParams, key, &encryptedKey)) return false;
} else {
if (!encryptWithoutKeymaster(appId, key, &encryptedKey)) return false;
}
if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
return true;
}
bool storeKeyAtomically(const std::string& key_path, const std::string& tmp_path,
const KeyAuthentication& auth, const KeyBuffer& key) {
if (pathExists(key_path)) {
LOG(ERROR) << "Already exists, cannot create key at: " << key_path;
return false;
}
if (pathExists(tmp_path)) {
LOG(DEBUG) << "Already exists, destroying: " << tmp_path;
destroyKey(tmp_path); // May be partially created so ignore errors
}
if (!storeKey(tmp_path, auth, key)) return false;
if (rename(tmp_path.c_str(), key_path.c_str()) != 0) {
PLOG(ERROR) << "Unable to move new key to location: " << key_path;
return false;
}
LOG(DEBUG) << "Created key: " << key_path;
return true;
}
bool retrieveKey(const std::string& dir, const KeyAuthentication& auth, KeyBuffer* key) {
std::string version;
if (!readFileToString(dir + "/" + kFn_version, &version)) return false;
if (version != kCurrentVersion) {
LOG(ERROR) << "Version mismatch, expected " << kCurrentVersion << " got " << version;
return false;
}
std::string secdiscardable_hash;
if (!readSecdiscardable(dir + "/" + kFn_secdiscardable, &secdiscardable_hash)) return false;
std::string stretching;
if (!readFileToString(dir + "/" + kFn_stretching, &stretching)) return false;
std::string salt;
if (stretchingNeedsSalt(stretching)) {
if (!readFileToString(dir + "/" + kFn_salt, &salt)) return false;
}
std::string appId;
if (!generateAppId(auth, stretching, salt, secdiscardable_hash, &appId)) return false;
std::string encryptedMessage;
if (!readFileToString(dir + "/" + kFn_encrypted_key, &encryptedMessage)) return false;
if (auth.usesKeymaster()) {
Keymaster keymaster;
if (!keymaster) return false;
auto keyParams = beginParams(auth, appId);
if (!decryptWithKeymasterKey(keymaster, dir, keyParams, encryptedMessage, key)) return false;
} else {
if (!decryptWithoutKeymaster(appId, encryptedMessage, key)) return false;
}
return true;
}
static bool deleteKey(const std::string& dir) {
std::string kmKey;
if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, &kmKey)) return false;
Keymaster keymaster;
if (!keymaster) return false;
if (!keymaster.deleteKey(kmKey)) return false;
return true;
}
bool runSecdiscardSingle(const std::string& file) {
if (ForkExecvp(
std::vector<std::string>{kSecdiscardPath, "--",
file}) != 0) {
LOG(ERROR) << "secdiscard failed";
return false;
}
return true;
}
static bool recursiveDeleteKey(const std::string& dir) {
if (ForkExecvp(std::vector<std::string>{kRmPath, "-rf", dir}) != 0) {
LOG(ERROR) << "recursive delete failed";
return false;
}
return true;
}
bool destroyKey(const std::string& dir) {
bool success = true;
// Try each thing, even if previous things failed.
bool uses_km = pathExists(dir + "/" + kFn_keymaster_key_blob);
if (uses_km) {
success &= deleteKey(dir);
}
auto secdiscard_cmd = std::vector<std::string>{
kSecdiscardPath, "--", dir + "/" + kFn_encrypted_key, dir + "/" + kFn_secdiscardable,
};
if (uses_km) {
secdiscard_cmd.emplace_back(dir + "/" + kFn_keymaster_key_blob);
}
if (ForkExecvp(secdiscard_cmd) != 0) {
LOG(ERROR) << "secdiscard failed";
success = false;
}
success &= recursiveDeleteKey(dir);
return success;
}
} // namespace vold
} // namespace android
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