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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 10 Jan 2022 18:54:57 +0100
Message-ID: <CAMuHMdX9nhUQe_jeQCUtXeQgcQ5MBiHpPiRexh86EssoHNtJ3Q@mail.gmail.com>
Subject: Re: [PATCH 08/17] ptrace/m68k: Stop open coding ptrace_report_syscall
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-Arch <linux-arch@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        Linux API <linux-api@vger.kernel.org>,
        Michael Schmitz <schmitzmic@gmail.com>,
        linux-m68k <linux-m68k@lists.linux-m68k.org>
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Hi Al,

CC Michael/m68k,

On Mon, Jan 10, 2022 at 5:20 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Mon, Jan 10, 2022 at 04:26:57PM +0100, Geert Uytterhoeven wrote:
> > On Mon, Jan 3, 2022 at 10:33 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
> > > The generic function ptrace_report_syscall does a little more
> > > than syscall_trace on m68k.  The function ptrace_report_syscall
> > > stops early if PT_TRACED is not set, it sets ptrace_message,
> > > and returns the result of fatal_signal_pending.
> > >
> > > Setting ptrace_message to a passed in value of 0 is effectively not
> > > setting ptrace_message, making that additional work a noop.
> > >
> > > Returning the result of fatal_signal_pending and letting the caller
> > > ignore the result becomes a noop in this change.
> > >
> > > When a process is ptraced, the flag PT_PTRACED is always set in
> > > current->ptrace.  Testing for PT_PTRACED in ptrace_report_syscall is
> > > just an optimization to fail early if the process is not ptraced.
> > > Later on in ptrace_notify, ptrace_stop will test current->ptrace under
> > > tasklist_lock and skip performing any work if the task is not ptraced.
> > >
> > > Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> > > Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> >
> > As this depends on the removal of a parameter from
> > ptrace_report_syscall() earlier in this series:
> > Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
>
> FWIW, I would suggest taking it a bit further: make syscall_trace_enter()
> and syscall_trace_leave() in m68k ptrace.c unconditional, replace the
> calls of syscall_trace() in entry.S with syscall_trace_enter() and
> syscall_trace_leave() resp. and remove syscall_trace().
>
> Geert, do you see any problems with that?  The only difference is that
> current->ptrace_message would be set to 1 for ptrace stop on entry and
> 2 - on leave.  Currently m68k just has it 0 all along.
>
> It is user-visible (the whole point is to let the tracer see which
> stop it is - entry or exit one), so somebody using PTRACE_GETEVENTMSG
> on syscall stops would start seeing 1 or 2 instead of "0 all along".
> That's how it works on all other architectures (including m68k-nommu),
> and I doubt that anything in userland will get broken.
>
> Behaviour of PTRACE_GETEVENTMSG for other stops (fork, etc.) remains
> as-is, of course.

In fact Michael did so in "[PATCH v7 1/2] m68k/kernel - wire up
syscall_trace_enter/leave for m68k"[1], but that's still stuck...

[1] https://lore.kernel.org/r/1624924520-17567-2-git-send-email-schmitzmic@gmail.com/

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds