On 2022/09/09 7:56, Casey Schaufler wrote: > Good idea. I'm reading the official how-to-write-a-syscall documentation. Can't we use prctl() syscall? We can assign an LSM ID when an (built-in or loadable) LSM is loaded, and pass that LSM ID as one of arguments for prctl(). Since we have security_task_prctl(option, arg2, arg3, arg4, arg5) inside prctl(), an LSM which was assigned that LSM ID upon load checks arguments (including PID argument). That will be something like ioctl() without open("/proc/pid/*/attr/*").