linux-kernel - Re: [PATCH v2 seccomp 1/6] seccomp: Move config option SECCOMP to arch/Kconfig

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Date:   Tue, 27 Oct 2020 10:52:39 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     YiFei Zhu <zhuyifei1999@...il.com>
Cc:     containers@...ts.linux-foundation.org,
        YiFei Zhu <yifeifz2@...inois.edu>, bpf <bpf@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dimitrios Skarlatos <dskarlat@...cmu.edu>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Hubertus Franke <frankeh@...ibm.com>,
        Jack Chen <jianyan2@...inois.edu>,
        Jann Horn <jannh@...gle.com>,
        Josep Torrellas <torrella@...inois.edu>,
        Kees Cook <keescook@...omium.org>,
        Tianyin Xu <tyxu@...inois.edu>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Tycho Andersen <tycho@...ho.pizza>,
        Valentin Rothberg <vrothber@...hat.com>,
        Will Drewry <wad@...omium.org>
Subject: Re: [PATCH v2 seccomp 1/6] seccomp: Move config option SECCOMP to arch/Kconfig

Hi Yifei,

On Thu, Sep 24, 2020 at 2:48 PM YiFei Zhu <zhuyifei1999@...il.com> wrote:
> From: YiFei Zhu <yifeifz2@...inois.edu>
>
> In order to make adding configurable features into seccomp
> easier, it's better to have the options at one single location,
> considering easpecially that the bulk of seccomp code is
> arch-independent. An quick look also show that many SECCOMP
> descriptions are outdated; they talk about /proc rather than
> prctl.
>
> As a result of moving the config option and keeping it default
> on, architectures arm, arm64, csky, riscv, sh, and xtensa
> did not have SECCOMP on by default prior to this and SECCOMP will
> be default in this change.
>
> Architectures microblaze, mips, powerpc, s390, sh, and sparc
> have an outdated depend on PROC_FS and this dependency is removed
> in this change.
>
> Suggested-by: Jann Horn <jannh@...gle.com>
> Link: https://lore.kernel.org/lkml/CAG48ez1YWz9cnp08UZgeieYRhHdqh-ch7aNwc4JRBnGyrmgfMg@mail.gmail.com/
> Signed-off-by: YiFei Zhu <yifeifz2@...inois.edu>

Thanks for your patch. which is now commit 282a181b1a0d66de ("seccomp:
Move config option SECCOMP to arch/Kconfig") in v5.10-rc1.

> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -458,6 +462,23 @@ config HAVE_ARCH_SECCOMP_FILTER
>             results in the system call being skipped immediately.
>           - seccomp syscall wired up
>
> +config SECCOMP
> +       def_bool y
> +       depends on HAVE_ARCH_SECCOMP
> +       prompt "Enable seccomp to safely compute untrusted bytecode"
> +       help
> +         This kernel feature is useful for number crunching applications
> +         that may need to compute untrusted bytecode during their
> +         execution. By using pipes or other transports made available to
> +         the process as file descriptors supporting the read/write
> +         syscalls, it's possible to isolate those applications in
> +         their own address space using seccomp. Once seccomp is
> +         enabled via prctl(PR_SET_SECCOMP), it cannot be disabled
> +         and the task is only allowed to execute a few safe syscalls
> +         defined by each seccomp mode.
> +
> +         If unsure, say Y. Only embedded should say N here.
> +

Please tell me why SECCOMP is special, and deserves to default to be
enabled.  Is it really that critical, given only 13.5 (half of sparc
;-) out of 24
architectures implement support for it?

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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