Specifically, PRIVEXEC ensures that a private process
can write data via IPC only to the other members of its
group that share the same privacy context. In other words,
a private process cannot write data to a public process, or
to an unrelated private process.
As usual, public processes can freely exchange data with
other public processes. Note that public processes can also
write data to private processes, since data flow from a public
process to a private process does not violate the security
properties of PRIVEXEC