keymaster/4.0/vts/functional/BootloaderStateTest.cpp

/*
 * Copyright (C) 2023 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 <memory>
#include <optional>
#include <string>
#include <vector>

#include <android-base/properties.h>
#include <fstab/fstab.h>
#include <libavb/libavb.h>
#include <libavb_user/avb_ops_user.h>

#include "KeymasterHidlTest.h"

namespace android::hardware::keymaster::V4_0::test {

using ::std::string;
using ::std::vector;

// Since this test needs to talk to Keymaster HAL, it can only run as root. Thus,
// bootloader can not be locked.
class BootloaderStateTest : public KeymasterHidlTest {
  public:
    virtual void SetUp() override {
        KeymasterHidlTest::SetUp();

        // Generate a key.
        auto ec = GenerateKey(AuthorizationSetBuilder()
                                      .Authorization(TAG_NO_AUTH_REQUIRED)
                                      .EcdsaSigningKey(EcCurve::P_256)
                                      .Digest(Digest::SHA_2_256));
        ASSERT_EQ(ec, ErrorCode::OK) << "Failed to generate key.";

        // Generate attestation.
        hidl_vec<hidl_vec<uint8_t>> cert_chain;
        ec = AttestKey(AuthorizationSetBuilder()
                               .Authorization(TAG_ATTESTATION_CHALLENGE, HidlBuf("challenge"))
                               .Authorization(TAG_ATTESTATION_APPLICATION_ID, HidlBuf("foo")),
                       &cert_chain);
        ASSERT_EQ(ec, ErrorCode::OK) << "Failed to generate attestation.";

        X509_Ptr cert(parse_cert_blob(cert_chain[0]));
        ASSERT_TRUE(cert.get()) << "Failed to parse certificate blob.";

        ASN1_OCTET_STRING* attest_rec = get_attestation_record(cert.get());
        ASSERT_TRUE(attest_rec) << "Failed to get attestation record.";

        // Parse root of trust.
        auto result = parse_root_of_trust(attest_rec->data, attest_rec->length, &attestedVbKey_,
                                          &attestedVbState_, &attestedBootloaderState_,
                                          &attestedVbmetaDigest_);
        ASSERT_EQ(result, ErrorCode::OK) << "Failed to parse root of trust.";
    }

    hidl_vec<uint8_t> attestedVbKey_;
    keymaster_verified_boot_t attestedVbState_;
    bool attestedBootloaderState_;
    hidl_vec<uint8_t> attestedVbmetaDigest_;
};

// Check that attested bootloader state is set to unlocked.
TEST_P(BootloaderStateTest, BootloaderIsUnlocked) {
    ASSERT_FALSE(attestedBootloaderState_)
            << "This test runs as root. Bootloader must be unlocked.";
}

// Check that verified boot state is set to "unverified", i.e. "orange".
TEST_P(BootloaderStateTest, VbStateIsUnverified) {
    // Unlocked bootloader implies that verified boot state must be "unverified".
    ASSERT_EQ(attestedVbState_, KM_VERIFIED_BOOT_UNVERIFIED)
            << "Verified boot state must be \"UNVERIFIED\" aka \"orange\".";

    // AVB spec stipulates that bootloader must set "androidboot.verifiedbootstate" parameter
    // on the kernel command-line. This parameter is exposed to userspace as
    // "ro.boot.verifiedbootstate" property.
    auto vbStateProp = ::android::base::GetProperty("ro.boot.verifiedbootstate", "");
    ASSERT_EQ(vbStateProp, "orange")
            << "Verified boot state must be \"UNVERIFIED\" aka \"orange\".";
}

// Following error codes from avb_slot_data() mean that slot data was loaded
// (even if verification failed).
static inline bool avb_slot_data_loaded(AvbSlotVerifyResult result) {
    switch (result) {
        case AVB_SLOT_VERIFY_RESULT_OK:
        case AVB_SLOT_VERIFY_RESULT_ERROR_VERIFICATION:
        case AVB_SLOT_VERIFY_RESULT_ERROR_ROLLBACK_INDEX:
        case AVB_SLOT_VERIFY_RESULT_ERROR_PUBLIC_KEY_REJECTED:
            return true;
        default:
            return false;
    }
}

// Check that attested vbmeta digest is correct.
TEST_P(BootloaderStateTest, VbmetaDigest) {
    AvbSlotVerifyData* avbSlotData;
    auto suffix = fs_mgr_get_slot_suffix();
    const char* partitions[] = {nullptr};
    auto avbOps = avb_ops_user_new();

    // For VTS, devices run with vendor_boot-debug.img, which is not release key
    // signed. Use AVB_SLOT_VERIFY_FLAGS_ALLOW_VERIFICATION_ERROR to bypass avb
    // verification errors. This is OK since we only care about the digest for
    // this test case.
    auto result = avb_slot_verify(avbOps, partitions, suffix.c_str(),
                                  AVB_SLOT_VERIFY_FLAGS_ALLOW_VERIFICATION_ERROR,
                                  AVB_HASHTREE_ERROR_MODE_EIO, &avbSlotData);
    ASSERT_TRUE(avb_slot_data_loaded(result)) << "Failed to load avb slot data";

    // Unfortunately, bootloader is not required to report the algorithm used
    // to calculate the digest. There are only two supported options though,
    // SHA256 and SHA512. Attested VBMeta digest must match one of these.
    vector<uint8_t> digest256(AVB_SHA256_DIGEST_SIZE);
    vector<uint8_t> digest512(AVB_SHA512_DIGEST_SIZE);

    avb_slot_verify_data_calculate_vbmeta_digest(avbSlotData, AVB_DIGEST_TYPE_SHA256,
                                                 digest256.data());
    avb_slot_verify_data_calculate_vbmeta_digest(avbSlotData, AVB_DIGEST_TYPE_SHA512,
                                                 digest512.data());

    ASSERT_TRUE((attestedVbmetaDigest_ == digest256) || (attestedVbmetaDigest_ == digest512))
            << "Attested digest does not match computed digest.";
}

INSTANTIATE_KEYMASTER_HIDL_TEST(BootloaderStateTest);

}  // namespace android::hardware::keymaster::V4_0::test