Re: Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads

From: Al Viro
Date: Mon Jun 21 2021 - 09:55:17 EST

On Tue, Jun 15, 2021 at 02:58:12PM -0700, Linus Torvalds wrote:

> And I think our horrible "kernel threads return to user space when
> done" is absolutely horrifically nasty. Maybe of the clever sort, but
> mostly of the historical horror sort.

How would you prefer to handle that, then? Separate magical path from
kernel_execve() to switch to userland? We used to have something of
that sort, and that had been a real horror...

As it is, it's "kernel thread is spawned at the point similar to
ret_from_fork(), runs the payload (which almost never returns) and
then proceeds out to userland, same way fork(2) would've done."
That way kernel_execve() doesn't have to do anything magical.

Al, digging through the old notes and current call graph...