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From: Jann Horn <jannh@google.com>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
	lkml <linux-kernel@vger.kernel.org>,
	linux-man <linux-man@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Florian Weimer <fweimer@redhat.com>,
	Oleg Nesterov <oleg@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
	David Howells <dhowells@redhat.com>,
	Pavel Emelyanov <xemul@virtuozzo.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Adrian Reber <adrian@lisas.de>, Andrei Vagin <avagin@gmail.com>,
	Linux API <linux-api@vger.kernel.org>
Subject: Re: For review: documentation of clone3() system call
Date: Mon, 28 Oct 2019 20:09:13 +0100
Message-ID: <CAG48ez20hn8vToY+=C62nA-rbUfxh=JD6N-f7XVS3_GZOoPjxw@mail.gmail.com> (raw)
In-Reply-To: <20191028172143.4vnnjpdljfnexaq5@wittgenstein>

On Mon, Oct 28, 2019 at 6:21 PM Christian Brauner
<christian.brauner@ubuntu.com> wrote:
> On Mon, Oct 28, 2019 at 04:12:09PM +0100, Jann Horn wrote:
> > On Fri, Oct 25, 2019 at 6:59 PM Michael Kerrisk (man-pages)
> > <mtk.manpages@gmail.com> wrote:
> > > I've made a first shot at adding documentation for clone3(). You can
> > > see the diff here:
> > > https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=faa0e55ae9e490d71c826546bbdef954a1800969
[...]
> > You might want to note somewhere that its flags can't be
> > seccomp-filtered because they're stored in memory, making it
> > inappropriate to use in heavily sandboxed processes.
>
> Hm, I don't think that belongs on the clone manpage. Granted that
> process creation is an important syscall but so are a bunch of others
> that aren't filterable because of pointer arguments.
> We can probably mention on the seccomp manpage that seccomp can't filter
> on pointer arguments and then provide a list of examples. If you setup a
> seccomp filter and don't know that you can't filter syscalls with
> pointer args that seems pretty bad to begin with.

Fair enough.

[...]
> One thing I never liked about clone() was that userspace had to know
> about stack direction. And there is a lot of ugly code in userspace that
> has nasty clone() wrappers like:
[...]
> where stack + stack_size is addition on a void pointer which usually
> clang and gcc are not very happy about.
> I wanted to bring this up on the mailing list soon: If possible, I don't
> want userspace to need to know about stack direction and just have stack
> point to the beginning and then have the kernel do the + stack_size
> after the copy_clone_args_from_user() if the arch needs it. For example,
> by having a dumb helder similar to copy_thread_tls()/coyp_thread() that
> either does the + stack_size or not. Right now, clone3() is supported on
> parisc and afaict, the stack grows upwards for it. I'm not sure if there
> are obvious reasons why that won't work or it would be a bad idea...

That would mean adding a new clone flag that redefines how those
parameters work and describing the current behavior in the manpage as
the behavior without the flag (which doesn't exist on 5.3), right?

  reply index

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-25 16:59 Michael Kerrisk (man-pages)
2019-10-25 17:07 ` Christian Brauner
2019-11-07 12:26   ` Michael Kerrisk (man-pages)
2019-10-26  2:28 ` G. Branden Robinson
2019-10-31  6:06   ` Michael Kerrisk (man-pages)
2019-10-28 15:12 ` Jann Horn
2019-10-28 17:21   ` Christian Brauner
2019-10-28 19:09     ` Jann Horn [this message]
2019-10-29 11:27       ` Christian Brauner
2019-10-29 14:26         ` Christian Brauner
2019-10-29 14:36           ` Florian Weimer
2019-10-29 16:04             ` Christian Brauner
2019-10-29 15:20           ` Jann Horn
2019-10-29 16:05             ` Christian Brauner
2019-11-07 15:19 ` Christian Brauner
2019-11-07 16:10   ` Florian Weimer
2019-11-09  8:09   ` Michael Kerrisk (man-pages)
2019-11-09 16:53     ` Christian Brauner
2019-11-11  9:02       ` Michael Kerrisk (man-pages)
2019-11-11 11:36         ` Christian Brauner
2019-11-11 19:56           ` Michael Kerrisk (man-pages)
2019-11-11 14:55     ` Jann Horn
2019-11-11 16:58       ` Theodore Y. Ts'o
2019-11-11 20:24         ` Jann Horn
2019-11-12 23:03           ` Kees Cook
2019-11-14 12:15       ` Michael Kerrisk (man-pages)
2019-11-14 12:29         ` Christian Brauner
2019-11-11 15:03 ` Florian Weimer
2019-11-11 15:15   ` Jann Horn
2019-11-11 15:20     ` Florian Weimer

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