It looks like they currently use the `ssh_bind_options_set` function with `SSH_BIND_OPTIONS_HOSTKEY` to set the host keys which means they exist on disk at some point. HSM aside, I believe it would be possible to use the `ssh_bind_set_key` and deserialize them from a secret vault so they only exist in the memory of the ssh daemon.
Obviously they also just straight up have enough resources to fork the code and modify it to use an HSM.
Source: looking at their ssh server portion of `babeld` in ghidra right now as part of hunting for bug bounties.
It looks like they currently use the `ssh_bind_options_set` function with `SSH_BIND_OPTIONS_HOSTKEY` to set the host keys which means they exist on disk at some point. HSM aside, I believe it would be possible to use the `ssh_bind_set_key` and deserialize them from a secret vault so they only exist in the memory of the ssh daemon.
Obviously they also just straight up have enough resources to fork the code and modify it to use an HSM.
Source: looking at their ssh server portion of `babeld` in ghidra right now as part of hunting for bug bounties.