Re: Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads

[Linus Torvalds]

On Thu, Jun 10, 2021 at 1:58 PM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
>
> The problem is sometimes we read all of the registers from
> a context where they are not all saved.

Ouch. Yes. And this is really painful because none of the *normal*
architectures do this, so it gets absolutely no coverage.

> I think at this point we need to say that the architectures that have a
> do this need to be fixed to at least call do_exit and the kernel
> function in create_io_thread with the deeper stack.

Yeah. We traditionally have that requirement for fork() and friends
too (vfork/clone), so adding exit and io_uring to do so seems like the
most straightforward thing.

But I really wish we had some way to test and trigger this so that we
wouldn't get caught on this before. Something in task_pt_regs() that
catches "this doesn't actually work" and does a WARN_ON_ONCE() on the
affected architectures?

               Linus