1 /*
2 * Copyright (C) 2016 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16 #include "keystore_attestation_id.h"
17
18 #define LOG_TAG "keystore_att_id"
19
20 #include <cutils/log.h>
21
22 #include <memory>
23 #include <string>
24 #include <vector>
25
26 #include <binder/IServiceManager.h>
27 #include <binder/Parcel.h>
28 #include <binder/Parcelable.h>
29 #include <binder/PersistableBundle.h>
30
31 #include <android/security/keymaster/BpKeyAttestationApplicationIdProvider.h>
32 #include <android/security/keymaster/IKeyAttestationApplicationIdProvider.h>
33 #include <keystore/KeyAttestationApplicationId.h>
34 #include <keystore/KeyAttestationPackageInfo.h>
35 #include <keystore/Signature.h>
36
37 #include <private/android_filesystem_config.h> /* for AID_SYSTEM */
38
39 #include <openssl/asn1t.h>
40 #include <openssl/bn.h>
41 #include <openssl/sha.h>
42
43 #include <utils/String8.h>
44
45 namespace android {
46
47 namespace {
48
49 constexpr const char* kAttestationSystemPackageName = "AndroidSystem";
50
signature2SHA256(const content::pm::Signature & sig)51 std::vector<uint8_t> signature2SHA256(const content::pm::Signature& sig) {
52 std::vector<uint8_t> digest_buffer(SHA256_DIGEST_LENGTH);
53 SHA256(sig.data().data(), sig.data().size(), digest_buffer.data());
54 return digest_buffer;
55 }
56
57 using ::android::security::keymaster::BpKeyAttestationApplicationIdProvider;
58
59 class KeyAttestationApplicationIdProvider : public BpKeyAttestationApplicationIdProvider {
60 public:
61 KeyAttestationApplicationIdProvider();
62
63 static KeyAttestationApplicationIdProvider& get();
64
65 private:
66 android::sp<android::IServiceManager> service_manager_;
67 };
68
get()69 KeyAttestationApplicationIdProvider& KeyAttestationApplicationIdProvider::get() {
70 static KeyAttestationApplicationIdProvider mpm;
71 return mpm;
72 }
73
KeyAttestationApplicationIdProvider()74 KeyAttestationApplicationIdProvider::KeyAttestationApplicationIdProvider()
75 : BpKeyAttestationApplicationIdProvider(
76 android::defaultServiceManager()->getService(String16("sec_key_att_app_id_provider"))) {}
77
78 DECLARE_STACK_OF(ASN1_OCTET_STRING);
79
80 typedef struct km_attestation_package_info {
81 ASN1_OCTET_STRING* package_name;
82 ASN1_INTEGER* version;
83 } KM_ATTESTATION_PACKAGE_INFO;
84
85 ASN1_SEQUENCE(KM_ATTESTATION_PACKAGE_INFO) = {
86 ASN1_SIMPLE(KM_ATTESTATION_PACKAGE_INFO, package_name, ASN1_OCTET_STRING),
87 ASN1_SIMPLE(KM_ATTESTATION_PACKAGE_INFO, version, ASN1_INTEGER),
88 } ASN1_SEQUENCE_END(KM_ATTESTATION_PACKAGE_INFO);
89 IMPLEMENT_ASN1_FUNCTIONS(KM_ATTESTATION_PACKAGE_INFO);
90
91 DECLARE_STACK_OF(KM_ATTESTATION_PACKAGE_INFO);
92
93 typedef struct km_attestation_application_id {
94 STACK_OF(KM_ATTESTATION_PACKAGE_INFO) * package_infos;
95 STACK_OF(ASN1_OCTET_STRING) * signature_digests;
96 } KM_ATTESTATION_APPLICATION_ID;
97
98 ASN1_SEQUENCE(KM_ATTESTATION_APPLICATION_ID) = {
99 ASN1_SET_OF(KM_ATTESTATION_APPLICATION_ID, package_infos, KM_ATTESTATION_PACKAGE_INFO),
100 ASN1_SET_OF(KM_ATTESTATION_APPLICATION_ID, signature_digests, ASN1_OCTET_STRING),
101 } ASN1_SEQUENCE_END(KM_ATTESTATION_APPLICATION_ID);
102 IMPLEMENT_ASN1_FUNCTIONS(KM_ATTESTATION_APPLICATION_ID);
103
104 } // namespace
105
106 } // namespace android
107
108 namespace std {
109 template <> struct default_delete<android::KM_ATTESTATION_PACKAGE_INFO> {
operator ()std::default_delete110 void operator()(android::KM_ATTESTATION_PACKAGE_INFO* p) {
111 android::KM_ATTESTATION_PACKAGE_INFO_free(p);
112 }
113 };
114 template <> struct default_delete<ASN1_OCTET_STRING> {
operator ()std::default_delete115 void operator()(ASN1_OCTET_STRING* p) { ASN1_OCTET_STRING_free(p); }
116 };
117 template <> struct default_delete<android::KM_ATTESTATION_APPLICATION_ID> {
operator ()std::default_delete118 void operator()(android::KM_ATTESTATION_APPLICATION_ID* p) {
119 android::KM_ATTESTATION_APPLICATION_ID_free(p);
120 }
121 };
122 } // namespace std
123
124 namespace android {
125 namespace security {
126 namespace {
127
128 using ::android::security::keymaster::KeyAttestationApplicationId;
129 using ::android::security::keymaster::KeyAttestationPackageInfo;
130
build_attestation_package_info(const KeyAttestationPackageInfo & pinfo,std::unique_ptr<KM_ATTESTATION_PACKAGE_INFO> * attestation_package_info_ptr)131 status_t build_attestation_package_info(const KeyAttestationPackageInfo& pinfo,
132 std::unique_ptr<KM_ATTESTATION_PACKAGE_INFO>* attestation_package_info_ptr) {
133
134 if (!attestation_package_info_ptr) return BAD_VALUE;
135 auto& attestation_package_info = *attestation_package_info_ptr;
136
137 attestation_package_info.reset(KM_ATTESTATION_PACKAGE_INFO_new());
138 if (!attestation_package_info.get()) return NO_MEMORY;
139
140 if (!pinfo.package_name()) {
141 ALOGE("Key attestation package info lacks package name");
142 return BAD_VALUE;
143 }
144
145 std::string pkg_name(String8(*pinfo.package_name()).string());
146 if (!ASN1_OCTET_STRING_set(attestation_package_info->package_name,
147 reinterpret_cast<const unsigned char*>(pkg_name.data()),
148 pkg_name.size())) {
149 return UNKNOWN_ERROR;
150 }
151
152 BIGNUM* bn_version = BN_new();
153 if (bn_version == nullptr) {
154 return NO_MEMORY;
155 }
156 if (BN_set_u64(bn_version, static_cast<uint64_t>(pinfo.version_code())) != 1) {
157 BN_free(bn_version);
158 return UNKNOWN_ERROR;
159 }
160 status_t retval = NO_ERROR;
161 if (BN_to_ASN1_INTEGER(bn_version, attestation_package_info->version) == nullptr) {
162 retval = UNKNOWN_ERROR;
163 }
164 BN_free(bn_version);
165 return retval;
166 }
167
168 StatusOr<std::vector<uint8_t>>
build_attestation_application_id(const KeyAttestationApplicationId & key_attestation_id)169 build_attestation_application_id(const KeyAttestationApplicationId& key_attestation_id) {
170 auto attestation_id =
171 std::unique_ptr<KM_ATTESTATION_APPLICATION_ID>(KM_ATTESTATION_APPLICATION_ID_new());
172
173 auto attestation_pinfo_stack = reinterpret_cast<_STACK*>(attestation_id->package_infos);
174
175 if (key_attestation_id.pinfos_begin() == key_attestation_id.pinfos_end()) return BAD_VALUE;
176
177 for (auto pinfo = key_attestation_id.pinfos_begin(); pinfo != key_attestation_id.pinfos_end();
178 ++pinfo) {
179 if (!pinfo->package_name()) {
180 ALOGE("Key attestation package info lacks package name");
181 return BAD_VALUE;
182 }
183 std::string package_name(String8(*pinfo->package_name()).string());
184 std::unique_ptr<KM_ATTESTATION_PACKAGE_INFO> attestation_package_info;
185 auto rc = build_attestation_package_info(*pinfo, &attestation_package_info);
186 if (rc != NO_ERROR) {
187 ALOGE("Building DER attestation package info failed %d", rc);
188 return rc;
189 }
190 if (!sk_push(attestation_pinfo_stack, attestation_package_info.get())) {
191 return NO_MEMORY;
192 }
193 // if push succeeded, the stack takes ownership
194 attestation_package_info.release();
195 }
196
197 /** Apps can only share a uid iff they were signed with the same certificate(s). Because the
198 * signature field actually holds the signing certificate, rather than a signature, we can
199 * simply use the set of signature digests of the first package info.
200 */
201 const auto& pinfo = *key_attestation_id.pinfos_begin();
202 std::vector<std::vector<uint8_t>> signature_digests;
203
204 for (auto sig = pinfo.sigs_begin(); sig != pinfo.sigs_end(); ++sig) {
205 signature_digests.push_back(signature2SHA256(*sig));
206 }
207
208 auto signature_digest_stack = reinterpret_cast<_STACK*>(attestation_id->signature_digests);
209 for (auto si : signature_digests) {
210 auto asn1_item = std::unique_ptr<ASN1_OCTET_STRING>(ASN1_OCTET_STRING_new());
211 if (!asn1_item) return NO_MEMORY;
212 if (!ASN1_OCTET_STRING_set(asn1_item.get(), si.data(), si.size())) {
213 return UNKNOWN_ERROR;
214 }
215 if (!sk_push(signature_digest_stack, asn1_item.get())) {
216 return NO_MEMORY;
217 }
218 asn1_item.release(); // if push succeeded, the stack takes ownership
219 }
220
221 int len = i2d_KM_ATTESTATION_APPLICATION_ID(attestation_id.get(), nullptr);
222 if (len < 0) return UNKNOWN_ERROR;
223
224 std::vector<uint8_t> result(len);
225 uint8_t* p = result.data();
226 len = i2d_KM_ATTESTATION_APPLICATION_ID(attestation_id.get(), &p);
227 if (len < 0) return UNKNOWN_ERROR;
228
229 return result;
230 }
231
232 /* The following function are not used. They are mentioned here to silence
233 * warnings about them not being used.
234 */
235 void unused_functions_silencer() __attribute__((unused));
unused_functions_silencer()236 void unused_functions_silencer() {
237 i2d_KM_ATTESTATION_PACKAGE_INFO(nullptr, nullptr);
238 d2i_KM_ATTESTATION_APPLICATION_ID(nullptr, nullptr, 0);
239 d2i_KM_ATTESTATION_PACKAGE_INFO(nullptr, nullptr, 0);
240 }
241
242 } // namespace
243
gather_attestation_application_id(uid_t uid)244 StatusOr<std::vector<uint8_t>> gather_attestation_application_id(uid_t uid) {
245 KeyAttestationApplicationId key_attestation_id;
246
247 if (uid == AID_SYSTEM) {
248 /* Use a fixed ID for system callers */
249 auto pinfo = std::make_unique<KeyAttestationPackageInfo>(
250 String16(kAttestationSystemPackageName), 1 /* version code */,
251 std::make_shared<KeyAttestationPackageInfo::SignaturesVector>());
252 key_attestation_id = KeyAttestationApplicationId(std::move(pinfo));
253 } else {
254 /* Get the attestation application ID from package manager */
255 auto& pm = KeyAttestationApplicationIdProvider::get();
256 auto status = pm.getKeyAttestationApplicationId(uid, &key_attestation_id);
257 if (!status.isOk()) {
258 ALOGE("package manager request for key attestation ID failed with: %s %d",
259 status.exceptionMessage().string(), status.exceptionCode());
260 return FAILED_TRANSACTION;
261 }
262 }
263
264 /* DER encode the attestation application ID */
265 return build_attestation_application_id(key_attestation_id);
266 }
267
268 } // namespace security
269 } // namespace android
270