Is there any public implementation of dm-default-key module for android kernels?

Question

Android 9.0 states that there is some support for metadata encryption (https://source.android.com/security/encryption/metadata). This seems to require presence of some "dm-default-key" module. It appears that I did not find any reference of this module on my kernel (4.9), nor on those I browsed on the internet. Does anyone know where to find more information on how to implement it in the kernel? I have no specification on what it is expected to do, nor any reference implementation.

Answer 1

Here you go

https://github.com/kdrag0n/proton_bluecross/blob/master/drivers/md/dm-default-key.c

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Answer 2

Here it is on the most recent kernel for Pixel 3 XL devices:

https://android.googlesource.com/kernel/msm/+/refs/heads/android-msm-crosshatch-4.9-q-preview-6/drivers/md/dm-default-key.c