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

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Message-ID: <CAHk-=whAsWXcJkpMM8ji77DkYkeJAT4Cj98WBX-S6=GnMQwhzg@mail.gmail.com>
Date:   Mon, 21 Jun 2021 12:22:06 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Michael Schmitz <schmitzmic@...il.com>,
        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>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        Tejun Heo <tj@...nel.org>, Kees Cook <keescook@...omium.org>
Subject: Re: Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads

On Mon, Jun 21, 2021 at 11:59 AM Al Viro <viro@...iv.linux.org.uk> wrote:
>
>         There's a large mess around do_exit() - we have a bunch of
> callers all over arch/*; if nothing else, I very much doubt that really
> want to let tracer play with a thread in the middle of die_if_kernel()
> or similar.

Right you are.

I'm really beginning to hate ptrace_{event,notify}() and those
PTRACE_EVENT_xyz things.

I don't even know what uses them, honestly. How very annoying.

I guess it's easy enough (famous last words) to move the
ptrace_event() call out of do_exit() and into the actual
exit/exit_group system calls, and the signal handling path. The paths
that actually have proper pt_regs.

Looks like sys_exit() and do_group_exit() would be the two places to
do it (do_group_exit() would handle the signal case and
sys_group_exit()).

               Linus