On newer devices, use dm-default-key to encrypt SD cards

The dm-crypt solution requires a kernel patch that won't be present in
the GKI kernel, while the new metadata encryption system in the GKI
kernel solves this problem in a much cleaner way.

Test: create private volume on Cuttlefish, setting property both ways.
Bug: 147814592
Change-Id: Ie02bd647c38d8101af2bbc47637f65845d312cea

Android.bp

@@ -144,6 +144,7 @@ cc_library_static {
         "model/PublicVolume.cpp",
         "model/StubVolume.cpp",
         "model/VolumeBase.cpp",
+        "model/VolumeEncryption.cpp",
     ],
     product_variables: {
         arc: {

MetadataCrypt.cpp

@@ -186,9 +186,11 @@ static bool get_number_of_sectors(const std::string& real_blkdev, uint64_t* nr_s
 
 static bool create_crypto_blk_dev(const std::string& dm_name, const std::string& blk_device,
                                   const KeyBuffer& key, const CryptoOptions& options,
-                                  std::string* crypto_blkdev) {
-    uint64_t nr_sec;
-    if (!get_number_of_sectors(blk_device, &nr_sec)) return false;
+                                  std::string* crypto_blkdev, uint64_t* nr_sec) {
+    if (!get_number_of_sectors(blk_device, nr_sec)) return false;
+    // TODO(paulcrowley): don't hardcode that DmTargetDefaultKey uses 4096-byte
+    // sectors
+    *nr_sec &= ~7;
 
     KeyBuffer module_key;
     if (options.use_hw_wrapped_key) {
@@ -207,7 +209,7 @@ static bool create_crypto_blk_dev(const std::string& dm_name, const std::string&
     }
     std::string hex_key(hex_key_buffer.data(), hex_key_buffer.size());
 
-    auto target = std::make_unique<DmTargetDefaultKey>(0, nr_sec, options.cipher.get_kernel_name(),
+    auto target = std::make_unique<DmTargetDefaultKey>(0, *nr_sec, options.cipher.get_kernel_name(),
                                                        hex_key, blk_device, 0);
     if (options.is_legacy) target->SetIsLegacy();
     if (options.set_dun) target->SetSetDun();
@@ -316,13 +318,13 @@ bool fscrypt_mount_metadata_encrypted(const std::string& blk_device, const std::
     if (!read_key(data_rec->metadata_key_dir, gen, &key)) return false;
 
     std::string crypto_blkdev;
-    if (!create_crypto_blk_dev(kDmNameUserdata, data_rec->blk_device, key, options, &crypto_blkdev))
+    uint64_t nr_sec;
+    if (!create_crypto_blk_dev(kDmNameUserdata, data_rec->blk_device, key, options, &crypto_blkdev,
+                               &nr_sec))
         return false;
 
     // FIXME handle the corrupt case
     if (needs_encrypt) {
-        uint64_t nr_sec;
-        if (!get_number_of_sectors(data_rec->blk_device, &nr_sec)) return false;
         LOG(INFO) << "Beginning inplace encryption, nr_sec: " << nr_sec;
         off64_t size_already_done = 0;
         auto rc = cryptfs_enable_inplace(crypto_blkdev.data(), blk_device.data(), nr_sec,
@@ -343,5 +345,27 @@ bool fscrypt_mount_metadata_encrypted(const std::string& blk_device, const std::
     return true;
 }
 
+static bool get_volume_options(CryptoOptions* options) {
+    return parse_options(android::base::GetProperty("ro.crypto.volume.metadata.encryption", ""),
+                         options);
+}
+
+bool defaultkey_volume_keygen(KeyGeneration* gen) {
+    CryptoOptions options;
+    if (!get_volume_options(&options)) return false;
+    *gen = makeGen(options);
+    return true;
+}
+
+bool defaultkey_setup_ext_volume(const std::string& label, const std::string& blk_device,
+                                 const KeyBuffer& key, std::string* out_crypto_blkdev) {
+    LOG(DEBUG) << "defaultkey_setup_ext_volume: " << label << " " << blk_device;
+
+    CryptoOptions options;
+    if (!get_volume_options(&options)) return false;
+    uint64_t nr_sec;
+    return create_crypto_blk_dev(label, blk_device, key, options, out_crypto_blkdev, &nr_sec);
+}
+
 }  // namespace vold
 }  // namespace android

MetadataCrypt.h

@@ -19,12 +19,21 @@
 
 #include <string>
 
+#include "KeyBuffer.h"
+#include "KeyUtil.h"
+
 namespace android {
 namespace vold {
 
 bool fscrypt_mount_metadata_encrypted(const std::string& block_device,
                                       const std::string& mount_point, bool needs_encrypt);
 
+bool defaultkey_volume_keygen(KeyGeneration* gen);
+
+bool defaultkey_setup_ext_volume(const std::string& label, const std::string& blk_device,
+                                 const android::vold::KeyBuffer& key,
+                                 std::string* out_crypto_blkdev);
+
 }  // namespace vold
 }  // namespace android
 #endif

model/Disk.cpp

@@ -16,11 +16,11 @@
 
 #include "Disk.h"
 #include "FsCrypt.h"
-#include "KeyUtil.h"
 #include "PrivateVolume.h"
 #include "PublicVolume.h"
 #include "Utils.h"
 #include "VolumeBase.h"
+#include "VolumeEncryption.h"
 #include "VolumeManager.h"
 
 #include <android-base/file.h>
@@ -31,8 +31,6 @@
 #include <android-base/strings.h>
 #include <fscrypt/fscrypt.h>
 
-#include "cryptfs.h"
-
 #include <fcntl.h>
 #include <inttypes.h>
 #include <stdio.h>
@@ -507,7 +505,7 @@ status_t Disk::partitionMixed(int8_t ratio) {
     }
 
     KeyBuffer key;
-    if (!generateStorageKey(cryptfs_get_keygen(), &key)) {
+    if (!generate_volume_key(&key)) {
         LOG(ERROR) << "Failed to generate key";
         return -EIO;
     }

model/PrivateVolume.cpp

@@ -17,8 +17,8 @@
 #include "PrivateVolume.h"
 #include "EmulatedVolume.h"
 #include "Utils.h"
+#include "VolumeEncryption.h"
 #include "VolumeManager.h"
-#include "cryptfs.h"
 #include "fs/Ext4.h"
 #include "fs/F2fs.h"
 
@@ -75,9 +75,8 @@ status_t PrivateVolume::doCreate() {
 
     // TODO: figure out better SELinux labels for private volumes
 
-    int res = cryptfs_setup_ext_volume(getId().c_str(), mRawDevPath.c_str(), mKeyRaw, &mDmDevPath);
-    if (res != 0) {
-        PLOG(ERROR) << getId() << " failed to setup cryptfs";
+    if (!setup_ext_volume(getId(), mRawDevPath, mKeyRaw, &mDmDevPath)) {
+        LOG(ERROR) << getId() << " failed to setup metadata encryption";
         return -EIO;
     }
 

model/VolumeEncryption.cpp

@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 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.
+ */
+
+#include "VolumeEncryption.h"
+
+#include <string>
+
+#include <android-base/logging.h>
+#include <android-base/properties.h>
+
+#include "KeyBuffer.h"
+#include "KeyUtil.h"
+#include "MetadataCrypt.h"
+#include "cryptfs.h"
+
+namespace android {
+namespace vold {
+
+enum class VolumeMethod { kFailed, kCrypt, kDefaultKey };
+
+static VolumeMethod lookup_volume_method() {
+    constexpr uint64_t pre_gki_level = 29;
+    auto first_api_level =
+            android::base::GetUintProperty<uint64_t>("ro.product.first_api_level", 0);
+    auto method = android::base::GetProperty("ro.crypto.volume.metadata.method", "default");
+    if (method == "default") {
+        return first_api_level > pre_gki_level ? VolumeMethod::kDefaultKey : VolumeMethod::kCrypt;
+    } else if (method == "dm-default-key") {
+        return VolumeMethod::kDefaultKey;
+    } else if (method == "dm-crypt") {
+        if (first_api_level > pre_gki_level) {
+            LOG(ERROR) << "volume encryption method dm-crypt cannot be used, "
+                          "ro.product.first_api_level = "
+                       << first_api_level;
+            return VolumeMethod::kFailed;
+        }
+        return VolumeMethod::kCrypt;
+    } else {
+        LOG(ERROR) << "Unknown volume encryption method: " << method;
+        return VolumeMethod::kFailed;
+    }
+}
+
+static VolumeMethod volume_method() {
+    static VolumeMethod method = lookup_volume_method();
+    return method;
+}
+
+bool generate_volume_key(android::vold::KeyBuffer* key) {
+    KeyGeneration gen;
+    switch (volume_method()) {
+        case VolumeMethod::kFailed:
+            LOG(ERROR) << "Volume encryption setup failed";
+            return false;
+        case VolumeMethod::kCrypt:
+            gen = cryptfs_get_keygen();
+            break;
+        case VolumeMethod::kDefaultKey:
+            if (!defaultkey_volume_keygen(&gen)) return false;
+            break;
+    }
+    if (!generateStorageKey(gen, key)) return false;
+    return true;
+}
+
+bool setup_ext_volume(const std::string& label, const std::string& blk_device,
+                      const android::vold::KeyBuffer& key, std::string* out_crypto_blkdev) {
+    switch (volume_method()) {
+        case VolumeMethod::kFailed:
+            LOG(ERROR) << "Volume encryption setup failed";
+            return false;
+        case VolumeMethod::kCrypt:
+            return cryptfs_setup_ext_volume(label.c_str(), blk_device.c_str(), key,
+                                            out_crypto_blkdev) == 0;
+        case VolumeMethod::kDefaultKey:
+            return defaultkey_setup_ext_volume(label, blk_device, key, out_crypto_blkdev);
+    }
+}
+
+}  // namespace vold
+}  // namespace android

model/VolumeEncryption.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 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 <string>
+
+#include "KeyBuffer.h"
+
+namespace android {
+namespace vold {
+
+bool generate_volume_key(android::vold::KeyBuffer* key);
+
+bool setup_ext_volume(const std::string& label, const std::string& blk_device,
+                      const android::vold::KeyBuffer& key, std::string* out_crypto_blkdev);
+
+}  // namespace vold
+}  // namespace android