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Commit 097e6253 authored by A. Cody Schuffelen's avatar A. Cody Schuffelen
Browse files

C++ AIDL on-device GateKeeper / SharedSecret impl 

Because Keystore2 always requires valid auth tokens for user keys, this
copies and extends the existing in-guest GateKeeper implementation to
negotiate a shared secret key with Keymint in order to generate a
session key for signing auth tokens.

This implementation also uses AIDL rather than HIDL to interact with the
framework. It's also packaged in an APEX.

The files are cobbled together from a few sources:

- SoftGateKeeper.h is based on hardware/interfaces/gatekeeper/1.0/software/SoftGateKeeper.h
- GateKeeper.{cpp,h} are based on device/google/cuttlefish/guest/hals/gatekeeper/remote/remote_gatekeeper.{cpp,h}
- SharedSecret.{cpp,h} are based on device/google/cuttlefish/guest/hals/keymint/remote/remote_shared_secret.{cpp,h}
- Apex files are based on device/google/cuttlefish/guest/hals/keymint/rust/

Keymint modifications to use BOOT_TIME are lifted from

https://android-review.git.corp.google.com/c/platform/hardware/interfaces/+/2856649/6..8/security/keymint/aidl/default/ta/clock.rs#38

Bug: 332376454
Change-Id: I81845d5e6370bdddb1a24d67437964e03a5fb243
Test: Run with rust-nonsecure keymint on Cuttlefish
parent 776e39b7

gatekeeper/aidl/software/Android.bp

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package {

    // See: http://go/android-license-faq

    // A large-scale-change added 'default_applicable_licenses' to import

    // all of the 'license_kinds' from "hardware_interfaces_license"

    // to get the below license kinds:

    //   SPDX-license-identifier-Apache-2.0

    default_applicable_licenses: ["hardware_interfaces_license"],

}



cc_binary {

    name: "android.hardware.gatekeeper-service.nonsecure",

    cflags: [

        "-fvisibility=hidden",

        "-Wall",

        "-Werror",

    ],

    installable: false, // installed in APEX

    relative_install_path: "hw",

    shared_libs: [

        "android.hardware.gatekeeper-V1-ndk",

        "android.hardware.security.sharedsecret-V1-ndk",

        "lib_android_keymaster_keymint_utils",

        "libbase",

        "libbinder_ndk",

        "libcrypto",

        "libcutils",

        "libgatekeeper",

        "libhardware",

        "libkeymaster_portable",

        "liblog",

        "libutils",

    ],

    srcs: [

        "GateKeeper.cpp",

        "SharedSecret.cpp",

        "service.cpp",

    ],

    static_libs: ["libscrypt_static"],

    vendor: true,

}



prebuilt_etc {

    name: "gatekeeper_nonsecure_vintf",

    srcs: [

        "android.hardware.gatekeeper-service.nonsecure.xml",

        "android.hardware.security.sharedsecret-gatekeeper.xml",

    ],

    sub_dir: "vintf",

    installable: false,

}



prebuilt_etc {

    name: "android.hardware.gatekeeper-service.nonsecure.rc",

    src: "android.hardware.gatekeeper-service.nonsecure.rc",

    installable: false,

}



apex {

    name: "com.android.hardware.gatekeeper.nonsecure",

    binaries: ["android.hardware.gatekeeper-service.nonsecure"],

    certificate: ":com.google.cf.apex.certificate",

    file_contexts: "file_contexts",

    key: "com.google.cf.apex.key",

    manifest: "manifest.json",

    prebuilts: [

        "gatekeeper_nonsecure_vintf",

        "android.hardware.gatekeeper-service.nonsecure.rc",

    ],

    updatable: false,

    vendor: true,

}

gatekeeper/aidl/software/GateKeeper.cpp

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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.

 */

#define LOG_TAG "android.hardware.gatekeeper-service.nonsecure"



#include <endian.h>



#include <android-base/logging.h>



#include "GateKeeper.h"



using ::gatekeeper::EnrollRequest;

using ::gatekeeper::EnrollResponse;

using ::gatekeeper::ERROR_NONE;

using ::gatekeeper::ERROR_RETRY;

using ::gatekeeper::SizedBuffer;

using ::gatekeeper::VerifyRequest;

using ::gatekeeper::VerifyResponse;



namespace aidl::android::hardware::gatekeeper {



SizedBuffer vec2sized_buffer(const std::vector<uint8_t>& vec) {

    if (vec.size() == 0 || vec.size() > std::numeric_limits<uint32_t>::max()) {

        return {};

    }

    auto unused = new uint8_t[vec.size()];

    std::copy(vec.begin(), vec.end(), unused);

    return {unused, static_cast<uint32_t>(vec.size())};

}



void sizedBuffer2AidlHWToken(SizedBuffer& buffer,

                             android::hardware::security::keymint::HardwareAuthToken* aidlToken) {

    const hw_auth_token_t* authToken =

            reinterpret_cast<const hw_auth_token_t*>(buffer.Data<uint8_t>());

    aidlToken->challenge = authToken->challenge;

    aidlToken->userId = authToken->user_id;

    aidlToken->authenticatorId = authToken->authenticator_id;

    // these are in network order: translate to host

    aidlToken->authenticatorType =

            static_cast<android::hardware::security::keymint::HardwareAuthenticatorType>(

                    be32toh(authToken->authenticator_type));

    aidlToken->timestamp.milliSeconds = be64toh(authToken->timestamp);

    aidlToken->mac.insert(aidlToken->mac.begin(), std::begin(authToken->hmac),

                          std::end(authToken->hmac));

}



SoftGateKeeperDevice::SoftGateKeeperDevice(::gatekeeper::SoftGateKeeper& impl) : impl_(impl) {}



::ndk::ScopedAStatus SoftGateKeeperDevice::enroll(int32_t uid,

                                                  const std::vector<uint8_t>& currentPasswordHandle,

                                                  const std::vector<uint8_t>& currentPassword,

                                                  const std::vector<uint8_t>& desiredPassword,

                                                  GatekeeperEnrollResponse* rsp) {

    if (desiredPassword.size() == 0) {

        LOG(ERROR) << "Desired password size is 0";

        return ndk::ScopedAStatus(AStatus_fromServiceSpecificError(ERROR_GENERAL_FAILURE));

    }



    if (currentPasswordHandle.size() > 0) {

        if (currentPasswordHandle.size() != sizeof(::gatekeeper::password_handle_t)) {

            LOG(ERROR) << "Password handle has wrong length";

            return ndk::ScopedAStatus(AStatus_fromServiceSpecificError(ERROR_GENERAL_FAILURE));

        }

    }



    EnrollRequest request(uid, vec2sized_buffer(currentPasswordHandle),

                          vec2sized_buffer(desiredPassword), vec2sized_buffer(currentPassword));

    EnrollResponse response;

    impl_.Enroll(request, &response);

    if (response.error == ERROR_RETRY) {

        LOG(ERROR) << "Enroll response has a retry error";

        *rsp = {ERROR_RETRY_TIMEOUT, static_cast<int32_t>(response.retry_timeout), 0, {}};

        return ndk::ScopedAStatus::ok();

    } else if (response.error != ERROR_NONE) {

        LOG(ERROR) << "Enroll response has an error: " << response.error;

        return ndk::ScopedAStatus(AStatus_fromServiceSpecificError(ERROR_GENERAL_FAILURE));

    } else {

        const ::gatekeeper::password_handle_t* password_handle =

                response.enrolled_password_handle.Data<::gatekeeper::password_handle_t>();

        *rsp = {STATUS_OK,

                0,

                static_cast<int64_t>(password_handle->user_id),

                {response.enrolled_password_handle.Data<uint8_t>(),

                 (response.enrolled_password_handle.Data<uint8_t>() +

                  response.enrolled_password_handle.size())}};

    }

    return ndk::ScopedAStatus::ok();

}



::ndk::ScopedAStatus SoftGateKeeperDevice::verify(

        int32_t uid, int64_t challenge, const std::vector<uint8_t>& enrolledPasswordHandle,

        const std::vector<uint8_t>& providedPassword, GatekeeperVerifyResponse* rsp) {

    if (enrolledPasswordHandle.size() == 0) {

        LOG(ERROR) << "Enrolled password size is 0";

        return ndk::ScopedAStatus(AStatus_fromServiceSpecificError(ERROR_GENERAL_FAILURE));

    }



    if (enrolledPasswordHandle.size() > 0) {

        if (enrolledPasswordHandle.size() != sizeof(::gatekeeper::password_handle_t)) {

            LOG(ERROR) << "Password handle has wrong length";

            return ndk::ScopedAStatus(AStatus_fromServiceSpecificError(ERROR_GENERAL_FAILURE));

        }

    }



    VerifyRequest request(uid, challenge, vec2sized_buffer(enrolledPasswordHandle),

                          vec2sized_buffer(providedPassword));

    VerifyResponse response;

    impl_.Verify(request, &response);



    if (response.error == ERROR_RETRY) {

        LOG(ERROR) << "Verify request response gave retry error";

        *rsp = {ERROR_RETRY_TIMEOUT, static_cast<int32_t>(response.retry_timeout), {}};

        return ndk::ScopedAStatus::ok();

    } else if (response.error != ERROR_NONE) {

        LOG(ERROR) << "Verify request response gave error: " << response.error;

        return ndk::ScopedAStatus(AStatus_fromServiceSpecificError(ERROR_GENERAL_FAILURE));

    } else {

        // On Success, return GatekeeperVerifyResponse with Success Status, timeout{0} and

        // valid HardwareAuthToken.

        *rsp = {response.request_reenroll ? STATUS_REENROLL : STATUS_OK, 0, {}};

        // Convert the hw_auth_token_t to HardwareAuthToken in the response.

        sizedBuffer2AidlHWToken(response.auth_token, &rsp->hardwareAuthToken);

    }

    return ndk::ScopedAStatus::ok();

}



::ndk::ScopedAStatus SoftGateKeeperDevice::deleteUser(int32_t /*uid*/) {

    LOG(ERROR) << "deleteUser is unimplemented";

    return ndk::ScopedAStatus(AStatus_fromServiceSpecificError(ERROR_NOT_IMPLEMENTED));

}



::ndk::ScopedAStatus SoftGateKeeperDevice::deleteAllUsers() {

    LOG(ERROR) << "deleteAllUsers is unimplemented";

    return ndk::ScopedAStatus(AStatus_fromServiceSpecificError(ERROR_NOT_IMPLEMENTED));

}



}  // namespace aidl::android::hardware::gatekeeper

gatekeeper/aidl/software/GateKeeper.h

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/*

 * Copyright (C) 2014 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.

 */

#pragma once



#include <aidl/android/hardware/gatekeeper/BnGatekeeper.h>

#include <gatekeeper/gatekeeper_messages.h>



#include "SoftGateKeeper.h"



namespace aidl::android::hardware::gatekeeper {



class SoftGateKeeperDevice : public BnGatekeeper {

  public:

    SoftGateKeeperDevice(::gatekeeper::SoftGateKeeper&);

    /**

     * Enrolls password_payload, which should be derived from a user selected pin

     * or password, with the authentication factor private key used only for

     * enrolling authentication factor data.

     *

     * Returns: 0 on success or an error code less than 0 on error.

     * On error, enrolled_password_handle will not be allocated.

     */

    ::ndk::ScopedAStatus enroll(int32_t uid, const std::vector<uint8_t>& currentPasswordHandle,

                                const std::vector<uint8_t>& currentPassword,

                                const std::vector<uint8_t>& desiredPassword,

                                GatekeeperEnrollResponse* _aidl_return) override;

    /**

     * Verifies provided_password matches enrolled_password_handle.

     *

     * Implementations of this module may retain the result of this call

     * to attest to the recency of authentication.

     *

     * On success, writes the address of a verification token to auth_token,

     * usable to attest password verification to other trusted services. Clients

     * may pass NULL for this value.

     *

     * Returns: 0 on success or an error code less than 0 on error

     * On error, verification token will not be allocated

     */

    ::ndk::ScopedAStatus verify(int32_t uid, int64_t challenge,

                                const std::vector<uint8_t>& enrolledPasswordHandle,

                                const std::vector<uint8_t>& providedPassword,

                                GatekeeperVerifyResponse* _aidl_return) override;



    ::ndk::ScopedAStatus deleteAllUsers() override;



    ::ndk::ScopedAStatus deleteUser(int32_t uid) override;



  private:

    ::gatekeeper::SoftGateKeeper& impl_;

};



}  // namespace aidl::android::hardware::gatekeeper

gatekeeper/aidl/software/SharedSecret.cpp

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/*

 * Copyright 2024, 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 "SharedSecret.h"



#include <algorithm>

#include <cstring>

#include <mutex>

#include <vector>



#include <openssl/rand.h>



#include <KeyMintUtils.h>

#include <aidl/android/hardware/security/sharedsecret/BnSharedSecret.h>

#include <aidl/android/hardware/security/sharedsecret/SharedSecretParameters.h>

#include <android-base/logging.h>

#include <keymaster/android_keymaster_messages.h>

#include <keymaster/android_keymaster_utils.h>

#include <keymaster/km_openssl/ckdf.h>

#include <keymaster/km_openssl/hmac.h>



namespace aidl::android::hardware::security::sharedsecret {



::ndk::ScopedAStatus SoftSharedSecret::getSharedSecretParameters(

        SharedSecretParameters* out_params) {

    std::lock_guard lock(mutex_);

    if (seed_.empty()) {

        seed_.resize(32, 0);

    }

    out_params->seed = seed_;

    if (nonce_.empty()) {

        nonce_.resize(32, 0);

        RAND_bytes(nonce_.data(), 32);

    }

    out_params->nonce = nonce_;

    LOG(INFO) << "Presented shared secret parameters with seed size " << out_params->seed.size()

              << " and nonce size " << out_params->nonce.size();

    return ::ndk::ScopedAStatus::ok();

}



::ndk::ScopedAStatus SoftSharedSecret::computeSharedSecret(

        const std::vector<SharedSecretParameters>& params, std::vector<uint8_t>* sharing_check) {

    std::lock_guard lock(mutex_);

    LOG(INFO) << "Computing shared secret";

    // Reimplemented based on SoftKeymasterEnforcement, which does not expose

    // enough functionality to satisfy the GateKeeper interface

    keymaster::KeymasterKeyBlob key_agreement_key;

    if (key_agreement_key.Reset(32) == nullptr) {

        LOG(ERROR) << "key agreement key memory allocation failed";

        return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_MEMORY_ALLOCATION_FAILED);

    }

    // Matching:

    // - kFakeAgreementKey in system/keymaster/km_openssl/soft_keymaster_enforcement.cpp

    // - Keys::kak in hardware/interfaces/security/keymint/aidl/default/ta/soft.rs

    std::memset(key_agreement_key.writable_data(), 0, 32);

    keymaster::KeymasterBlob label((uint8_t*)KEY_AGREEMENT_LABEL, strlen(KEY_AGREEMENT_LABEL));

    if (label.data == nullptr) {

        LOG(ERROR) << "label memory allocation failed";

        return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_MEMORY_ALLOCATION_FAILED);

    }



    static_assert(sizeof(keymaster_blob_t) == sizeof(keymaster::KeymasterBlob));



    bool found_mine = false;

    std::vector<keymaster::KeymasterBlob> context_blobs;

    for (const auto& param : params) {

        auto& seed_blob = context_blobs.emplace_back();

        if (seed_blob.Reset(param.seed.size()) == nullptr) {

            LOG(ERROR) << "seed memory allocation failed";

            return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_MEMORY_ALLOCATION_FAILED);

        }

        std::copy(param.seed.begin(), param.seed.end(), seed_blob.writable_data());

        auto& nonce_blob = context_blobs.emplace_back();

        if (nonce_blob.Reset(param.nonce.size()) == nullptr) {

            LOG(ERROR) << "Nonce memory allocation failed";

            return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_MEMORY_ALLOCATION_FAILED);

        }

        std::copy(param.nonce.begin(), param.nonce.end(), nonce_blob.writable_data());

        if (param.seed == seed_ && param.nonce == nonce_) {

            found_mine = true;

        }

    }

    if (!found_mine) {

        LOG(ERROR) << "Did not receive my own shared secret parameter back";

        return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_INVALID_ARGUMENT);

    }

    auto context_blobs_ptr = reinterpret_cast<keymaster_blob_t*>(context_blobs.data());

    if (hmac_key_.Reset(32) == nullptr) {

        LOG(ERROR) << "hmac key allocation failed";

        return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_MEMORY_ALLOCATION_FAILED);

    }

    auto error = keymaster::ckdf(key_agreement_key, label, context_blobs_ptr, context_blobs.size(),

                                 &hmac_key_);

    if (error != KM_ERROR_OK) {

        LOG(ERROR) << "CKDF failed";

        return keymint::km_utils::kmError2ScopedAStatus(error);

    }



    keymaster::HmacSha256 hmac_impl;

    if (!hmac_impl.Init(hmac_key_.key_material, hmac_key_.key_material_size)) {

        LOG(ERROR) << "hmac initialization failed";

        return ::ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);

    }

    sharing_check->clear();

    sharing_check->resize(32, 0);

    if (!hmac_impl.Sign((const uint8_t*)KEY_CHECK_LABEL, strlen(KEY_CHECK_LABEL),

                        sharing_check->data(), sharing_check->size())) {

        return ::ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);

    }

    return ::ndk::ScopedAStatus::ok();

}



keymaster::KeymasterKeyBlob SoftSharedSecret::HmacKey() const {

    std::lock_guard lock(mutex_);

    return hmac_key_;

}



}  // namespace aidl::android::hardware::security::sharedsecret

gatekeeper/aidl/software/SharedSecret.h

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/*

 * Copyright 2020, 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.

 */



#pragma once



#include <cstdint>

#include <mutex>



#include <aidl/android/hardware/security/sharedsecret/BnSharedSecret.h>

#include <aidl/android/hardware/security/sharedsecret/SharedSecretParameters.h>

#include <keymaster/km_openssl/soft_keymaster_enforcement.h>



namespace aidl::android::hardware::security::sharedsecret {



class SoftSharedSecret : public BnSharedSecret {

  public:

    ::ndk::ScopedAStatus getSharedSecretParameters(SharedSecretParameters* params) override;

    ::ndk::ScopedAStatus computeSharedSecret(const std::vector<SharedSecretParameters>& params,

                                             std::vector<uint8_t>* sharingCheck) override;



    keymaster::KeymasterKeyBlob HmacKey() const;



  private:

    mutable std::mutex mutex_;

    std::vector<std::uint8_t> seed_;

    std::vector<std::uint8_t> nonce_;

    keymaster::KeymasterKeyBlob hmac_key_;

};



}  // namespace aidl::android::hardware::security::sharedsecret