systrap

Overview ¶

Package systrap provides a seccomp-based implementation of the platform interface.

In a nutshell, it works as follows:

The creation of a new address space creates a new child processes.

The creation of a new stub thread creates a new system thread with a specified address space. To initialize this thread, the following action will be done:

• install a signal stack which is shared with the Sentry.
• install a signal handler for SYS, BUS, FPE, CHLD, TRAP, SEGV signals. This signal handler is a key part of the systrap platform. Any stub event which has to be handled in a privilege mode (by the Sentry) triggers one of previous signals. The signal handler is running on the separate stack which is shared with the Sentry. There is the sysmsg structure to synchronize the Sentry and a stub thread.
• install seccomp filters to trap user system calls.
• send a fake SIGSEGV to stop the thread in the signal handler.

A context is just a collection of temporary variables. Calling Switch on a context does the following:

Set up proper registers and an FPU state on a stub signal frame.
Wake up a stub thread by changing sysmsg->stage and calling FUTEX_WAKE.
Wait for new stub event by polling sysmsg->stage.

Lock order:

subprocessPool.mu
	subprocess.mu
		context.mu

+checkalignedignore