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      1 /*
      2  * Copyright (C) 2017 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 
     17 #ifndef __CORE_FS_MGR_AVB_H
     18 #define __CORE_FS_MGR_AVB_H
     19 
     20 #include <map>
     21 #include <memory>
     22 #include <string>
     23 
     24 #include <libavb/libavb.h>
     25 
     26 #include "fs_mgr.h"
     27 
     28 enum FsManagerAvbHandleStatus {
     29     kFsManagerAvbHandleUninitialized = -1,
     30     kFsManagerAvbHandleSuccess = 0,
     31     kFsManagerAvbHandleHashtreeDisabled = 1,
     32     kFsManagerAvbHandleErrorVerification = 2,
     33 };
     34 
     35 class FsManagerAvbOps;
     36 
     37 class FsManagerAvbHandle;
     38 using FsManagerAvbUniquePtr = std::unique_ptr<FsManagerAvbHandle>;
     39 
     40 using ByNameSymlinkMap = std::map<std::string, std::string>;
     41 
     42 // Provides a factory method to return a unique_ptr pointing to itself and the
     43 // SetUpAvb() function to extract dm-verity parameters from AVB metadata to
     44 // load verity table into kernel through ioctl.
     45 class FsManagerAvbHandle {
     46   public:
     47     // The factory method to return a FsManagerAvbUniquePtr that holds
     48     // the verified AVB (external/avb) metadata of all verified partitions
     49     // in avb_slot_data_.vbmeta_images[].
     50     //
     51     // The metadata is checked against the following values from /proc/cmdline.
     52     //   - androidboot.vbmeta.{hash_alg, size, digest}.
     53     //
     54     // A typical usage will be:
     55     //   - FsManagerAvbUniquePtr handle = FsManagerAvbHandle::Open();
     56     //
     57     // There are two overloaded Open() functions with a single parameter.
     58     // The argument can be a ByNameSymlinkMap describing the mapping from partition
     59     // name to by-name symlink, or a fstab file to which the ByNameSymlinkMap is
     60     // constructed from. e.g.,
     61     //   - /dev/block/platform/soc.0/7824900.sdhci/by-name/system_a ->
     62     //   - ByNameSymlinkMap["system_a"] = "/dev/block/platform/soc.0/7824900.sdhci/by-name/system_a"
     63     //
     64     // Possible return values:
     65     //   - nullptr: any error when reading and verifying the metadata,
     66     //     e.g., I/O error, digest value mismatch, size mismatch, etc.
     67     //
     68     //   - a valid unique_ptr with status kFsMgrAvbHandleHashtreeDisabled:
     69     //     to support the existing 'adb disable-verity' feature in Android.
     70     //     It's very helpful for developers to make the filesystem writable to
     71     //     allow replacing binaries on the device.
     72     //
     73     //   - a valid unique_ptr with status kFsMgrAvbHandleSuccess: the metadata
     74     //     is verified and can be trusted.
     75     //
     76     static FsManagerAvbUniquePtr Open(const fstab& fstab);
     77     static FsManagerAvbUniquePtr Open(ByNameSymlinkMap&& by_name_symlink_map);
     78 
     79     // Sets up dm-verity on the given fstab entry.
     80     // The 'wait_for_verity_dev' parameter makes this function wait for the
     81     // verity device to get created before return.
     82     // Returns true if the mount point is eligible to mount, it includes:
     83     //   - status_ is kFsMgrAvbHandleHashtreeDisabled or
     84     //   - status_ is kFsMgrAvbHandleSuccess and sending ioctl DM_TABLE_LOAD
     85     //     to load verity table is success.
     86     // Otherwise, returns false.
     87     bool SetUpAvb(fstab_rec* fstab_entry, bool wait_for_verity_dev);
     88 
     89     bool hashtree_disabled() const { return status_ == kFsManagerAvbHandleHashtreeDisabled; }
     90     const std::string& avb_version() const { return avb_version_; }
     91 
     92     FsManagerAvbHandle(const FsManagerAvbHandle&) = delete;             // no copy
     93     FsManagerAvbHandle& operator=(const FsManagerAvbHandle&) = delete;  // no assignment
     94 
     95     FsManagerAvbHandle(FsManagerAvbHandle&&) noexcept = delete;             // no move
     96     FsManagerAvbHandle& operator=(FsManagerAvbHandle&&) noexcept = delete;  // no move assignment
     97 
     98     ~FsManagerAvbHandle() {
     99         if (avb_slot_data_) {
    100             avb_slot_verify_data_free(avb_slot_data_);
    101         }
    102     };
    103 
    104   private:
    105     FsManagerAvbHandle() : avb_slot_data_(nullptr), status_(kFsManagerAvbHandleUninitialized) {}
    106     static FsManagerAvbUniquePtr DoOpen(FsManagerAvbOps* avb_ops);
    107 
    108     AvbSlotVerifyData* avb_slot_data_;
    109     FsManagerAvbHandleStatus status_;
    110     std::string avb_version_;
    111 };
    112 
    113 #endif /* __CORE_FS_MGR_AVB_H */
    114