linux-kernel - Re: [PATCH 0/2] Support compiling out the prctl syscall

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Date:   Tue, 8 Nov 2016 19:42:09 -0800
From:   Josh Triplett <josh@...htriplett.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Thomas Garnier <thgarnie@...gle.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Zefan Li <lizefan@...wei.com>,
        Li Bin <huawei.libin@...wei.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Alex Thorlton <athorlton@....com>,
        Michal Hocko <mhocko@...e.com>,
        Mateusz Guzik <mguzik@...hat.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        John Stultz <john.stultz@...aro.org>,
        Al Viro <viro@...iv.linux.org.uk>, Zach Brown <zab@...hat.com>,
        Anna Schumaker <Anna.Schumaker@...app.com>,
        Dave Hansen <dave.hansen@...el.com>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Nicolas Pitre <nico@...aro.org>
Subject: Re: [PATCH 0/2] Support compiling out the prctl syscall

On Wed, Nov 09, 2016 at 01:26:53AM +0100, Arnd Bergmann wrote:
> On Tuesday, November 8, 2016 4:17:47 PM CET Josh Triplett wrote:
> > Some embedded systems can do without the prctl syscall, saving some space.
> > 
> > This also avoids regular increases in tinyconfig size as people add more
> > non-optional functionality to prctl (observed via the 0-day kernel
> > infrastructure).
> > 
> > The first patch moves prctl and all its helpers into a separate source file,
> > kernel/prctl.c, to allow making it optional via the Makefile without any
> > ifdefs.  The second patch adds the Kconfig option to make prctl optional.
> > 
> > Josh Triplett (2):
> >   kernel: Move prctl and helpers from kernel/sys.c to new kernel/prctl.c
> >   kernel: Support compiling out the prctl syscall
> > 
> 
> Both of these look really nice to me. Another syscall that comes to
> mind as a candidate to be made optional is ptrace, and I've added
> Nicolas Pitre to Cc here, as he has looked into this before.

I've looked at that as well; it's a rather more complex patch, as
several other bits of the kernel hook into ptrace or otherwise depend on
ptrace.  (And ptrace_may_access will need to stick around even when
ptrace doesn't.)

- Josh Triplett