HiBoth ARM[1] and Intel[2] have features to hide parts of the address space from the rest of the program. The motivation of these hardware features is typically to hide the data of the app from a library or vice-versa. Both of them use unused bits in the PageTableEntry to store news (about 4 bits) in size. ARM's feature is called MTE and there is no hardware yet which supports this, Intel has been shipping chips with MPK for a few years.
Has the Genode community thought about how such a feature could be implemented in Genode? If not, I will start digging in and reach out as I run into issues. I would suspect it would affect the RM and DS cap types.
Best,
Sid