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

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Date:   Tue, 6 Mar 2018 20:01:21 +0000
From:   Andy Lutomirski <luto@...nel.org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        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 Tue, Mar 6, 2018 at 1:34 AM, Alexei Starovoitov <ast@...nel.org> wrote:
> As the first step in development of bpfilter project [1] the request_module()
> code is extended to allow user mode helpers to be invoked. Idea is that
> user mode helpers are built as part of the kernel build and installed as
> traditional kernel modules with .ko file extension into distro specified
> location, such that from a distribution point of view, they are no different
> than regular kernel modules. Thus, allow request_module() logic to load such
> user mode helper (umh) modules via:
>
>   request_module("foo") ->
>     call_umh("modprobe foo") ->
>       sys_finit_module(FD of /lib/modules/.../foo.ko) ->
>         call_umh(struct file)
>

I assume I'm missing some context here, but why does this need to be
handled by the kernel rather than, say, a change to how modprobe
works?  I imagine that usermode tooling needs to change regardless
because the existing tools may get rather confused if a .ko "module"
is really a dynamically liked program.  I notice that you're using
ET_EXEC in your example, and that will probably avoid problems, but I
imagine that some distros would much rather use ET_DYN.