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    Introduce new sepolicy injection mechanism · 49f25906
    topjohnwu authored
    In the current implementation, Magisk will either have to recreate
    all early mount implementation (for legacy SAR and rootfs devices) or
    delegate early mount to first stage init (for 2SI devices) to access
    required partitions for loading sepolicy. It then has to recreate the
    split sepolicy loading implementation in-house, apply patches, then
    dump the compiled + patched policies into monolithic format somewhere.
    Finally, it patches the original init to force it to load the sepolicy
    file we just created.
    
    With the increasing complexity involved in early mount and split
    sepolicy (there is even APEX module involved in the future!),
    it is about time to rethink Magisk's sepolicy strategy as rebuilding
    init's functionality is not scalable and easy to maintain.
    
    In this commit, instead of building sepolicy ourselves, we mock
    selinuxfs with FIFO files connected to a pre-init daemon, waiting
    for the actual init process to directly write the sepolicy file into
    MagiskInit. We then patch the file and load it into the kernel. Some
    FIFO tricks has to be used to hijack the original init process's
    control flow and prevent race conditions, details are directly in the
    comments in code.
    
    At the moment, only system-as-root (read-only root) support is added.
    Support for legacy rootfs devices will come with a follow up commit.
    49f25906
files.hpp 4.43 KB