It's unusual but certainly not novel. There have been similar attacks against e.g. server network cards >10 years ago, where (IIRC) a magic pattern used for factory testing could put the card into firmware download mode, and from there it had access to RAM, so game over
It's only in relatively recent times that shared memory interfaces have fallen under the security spotlight as new scenarios arise where a trusted driver may not be speaking to a trusted piece of hardware (e.g. virtualization), so there are plenty of attacks around that involve hopping across an interface assumed to have been free of trust boundaries (Firewire is another example kinda like this)
It's only in relatively recent times that shared memory interfaces have fallen under the security spotlight as new scenarios arise where a trusted driver may not be speaking to a trusted piece of hardware (e.g. virtualization), so there are plenty of attacks around that involve hopping across an interface assumed to have been free of trust boundaries (Firewire is another example kinda like this)