Thanks for reaching out!
Please let me see if I can find the location of Ostro's kernel in its BSP. If I find something useful I'll post it here.
I've an update for your case.
I've found a very useful guide for modifying Ostro's kernel, I'd suggest you to check it, you can find it in https://ostroproject.org/documentation/howtos/modifying-ostro-kernel.html.
Also, I must point out that any modifications to Joule's image and its kernel are not supported by us. Nevertheless, I encourage you to continue with your project and share your findings with the community, other user might find them useful.
Please let me know if that helps you.