linux-kernel - Re: [PATCH net-next] modules: allow modprobe load regular elf binaries

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Message-ID: <20180309012530.rk2m5kmpab7eb5fe@ast-mbp>
Date:   Thu, 8 Mar 2018 17:25:32 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Alexei Starovoitov <ast@...com>, Kees Cook <keescook@...omium.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Djalal Harouni <tixxdz@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@...com,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH net-next] modules: allow modprobe load regular elf
 binaries

On Fri, Mar 09, 2018 at 01:04:39AM +0000, Andy Lutomirski wrote:
> On Fri, Mar 9, 2018 at 12:57 AM, Alexei Starovoitov <ast@...com> wrote:
> > On 3/8/18 4:24 PM, Kees Cook wrote:
> >>
> >> As Andy asked earlier, why not DYN too to catch PIE executables? Seems
> >> like forcing the userspace helper to be non-PIE would defeat some of
> >> the userspace defenses in use in most distros.
> >
> >
> > because we don't add features without concrete users.
> 
> I disagree here.  If you're going to add a magic trick that triggers
> an execve(), then I think you should either support *both* standard,
> widely-used types of ELF programs or you should give a compelling use
> case that works for ET_EXEC but not for ET_DYN.  Keep in mind that
> many distros have a very strong preference for ET_DYN.

misunderstanding here is that this bpfiler.ko is part of _kernel build_.
Kernel decides how it's build.
Nothing to do with distros.
Current Makefile is very dumb and it's built with HOSTCC:
https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git/tree/net/bpfilter/Makefile?h=ipt_bpf
but it will be standalone with CC before final to make sure crosscompiling works.