linux-kernel - Re: [PATCH v4 1/2] Provide in-kernel headers for making it easy to extend the kernel

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Message-ID: <20190309121141.GA30173@kroah.com>
Date:   Sat, 9 Mar 2019 13:11:41 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexei Starovoitov <ast@...nel.org>,
        atish patra <atishp04@...il.com>,
        Daniel Colascione <dancol@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Guenter Roeck <groeck@...omium.org>,
        Jonathan Corbet <corbet@....net>,
        Karim Yaghmour <karim.yaghmour@...rsys.com>,
        Kees Cook <keescook@...omium.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        linux-trace-devel@...r.kernel.org,
        Manoj Rao <linux@...ojrajarao.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Qais Yousef <qais.yousef@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Shuah Khan <shuah@...nel.org>, Yonghong Song <yhs@...com>
Subject: Re: [PATCH v4 1/2] Provide in-kernel headers for making it easy to
 extend the kernel

On Sat, Mar 09, 2019 at 12:40:01PM +0100, Geert Uytterhoeven wrote:
> > Signing keys should be kept secure, or better yet, just deleted entirely
> > after creating and signing with them.  That's what I do for my kernels
> > and I'm pretty sure that some distros also do this.  That way there's no
> > chance that someone else can sign a module and have it loaded without
> > detection, which is what signing is supposed to prevent from happening.
> 
> If you want that kind of security, there's no point in allowing to extend the
> kernel by building more kernel modules after deployment.

That's not what these files are for (in the original user's case).  They
want these for doing tracing/ebpf stuff, which require kernel headers to
build against.

> "Raw kernel headers also cannot be copied into the filesystem like they
>  can be on other distros, due to licensing and other issues. There's no
>  linux-headers package on Android."
> 
> What's the licensing issue? What's the (legal) difference between having
> the headers on the file system, and having a kernel module including the
> headers on the file system?

There is no licensing issue, see my follow-up comment about that.

It's all in ease-of-use here.  You want to build a trace function
against a running kernel, and now you have the header files for that
specific kernel right there in the kernel itself to build against.  It
doesn't get easier than that.

thanks,

greg k-h