Re: Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads

[Michael Schmitz <schmitzmic@gmail.com>]

Hi Eric,

On 23/06/21 9:02 am, Eric W. Biederman wrote:
> Linus Torvalds <torvalds@linux-foundation.org> writes:
>
> So I was more thinking of the debug patch for m68k to catch all the
> _regular_ cases, and all the other random cases of ptrace_event() or
> ptrace_notify().
>
> Although maybe we've really caught them all. The exit case was clearly
> missing, and the thread fork case was scrogged. There are patches for
> the known problems. The patches I really don't like are the
> verification ones to find any unknown ones..
> We still have nios2 which copied the m68k logic at some point.  I think
> that is a processor that is still ``shipping'' and that people might
> still be using in new designs.
>
> I haven't looked closely enough to see what the other architectures with
> caller saved registers are doing.
>
> The challenging ones are /proc/pid/syscall and seccomp which want to see
> all of the system call arguments.  I think every architecture always
> saves the system call arguments unconditionally, so those cases are
> probably not as interesting.  But they certain look like they could be
> trouble.

Seccomp hasn't yet been implemented on m68k, though I'm working on that 
with Adrian. The sole secure_computing() call will happen in 
syscall_trace_enter(), so all system call arguments have been saved on 
the stack.

Haven't looked at /proc/pid/syscall yet ...

Cheers,

     Michael

> Eric
>