linux-kernel - Re: Kernel stack read with PTRACE_EVENT_EXIT and io

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Date:   Wed, 23 Jun 2021 09:48:40 +1200
From:   Michael Schmitz <schmitzmic@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        linux-arch <linux-arch@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>, Oleg Nesterov <oleg@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        alpha <linux-alpha@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Arnd Bergmann <arnd@...nel.org>, Tejun Heo <tj@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Subject: Re: Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads

Hi Eric,

On 23/06/21 9:02 am, Eric W. Biederman wrote:
> Linus Torvalds <torvalds@...ux-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
>