Re: [PATCH v1 1/3] Add the latent_entropy gcc plugin

From: Hector Martin <marcan@marcan.st>
To: re.emese@gmail.com
Cc: kernel-hardening@lists.openwall.com,
	LKML <linux-kernel@vger.kernel.org>,
	keescook@chromium.org, spender@grsecurity.net,
	pageexec@freemail.hu
Subject: Re: [PATCH v1 1/3] Add the latent_entropy gcc plugin
Date: Mon, 30 May 2016 02:59:36 +0900	[thread overview]
Message-ID: <a0e27065-afec-d82f-c478-1c311adaea3d@marcan.st> (raw)
In-Reply-To: 20160524001529.0e69232eff0b1b5bc566a763@gmail.com

On Mon, May 23, 2016 at 3:15 PM, Emese Revfy <re.emese@gmail.com> wrote:
> +/*
> + * Copyright 2012-2016 by the PaX Team <pageexec@freemail.hu>
> + * Copyright 2016 by Emese Revfy <re.emese@gmail.com>
> + * Licensed under the GPL v2
> + *
> + * Note: the choice of the license means that the compilation process is
> + *       NOT 'eligible' as defined by gcc's library exception to the GPL v3,
> + *       but for the kernel it doesn't matter since it doesn't link against
> + *       any of the gcc libraries
> + *
> + * gcc plugin to help generate a little bit of entropy from program state,
> + * used throughout the uptime of the kernel

The "Note" seems misleading. Since this is a GCC plugin, and directly
uses GCC's internal interfaces, doesn't that make it a derived work of
GCC, and thus, require that it be licensed under GPLv3 instead of GPLv2
(which is incompatible)?

AFAIK this is how the GPLv3 works in this context, and the GCC exception
doesn't change that because it only applies to libgcc and friends (and
does not weaken the default effects of the GPL over the rest of GCC). My
understanding is that the whole "eligible compilation" licensing hack
was designed to hinder non-linking proprietary compilation passes that
operate over data files containing an internal GCC representation, but
plain old loaded plugins still need to be GPLv3 regardless of whether
you link the end result to libgcc or not.

(Also, don't some arches link against libgcc, further complicating this?
Trying to use this compiler plugin with those arches would wind up with
non-redistributable kernels, this time due to the exception.)

-- 
Hector Martin (marcan@marcan.st)
Public Key: https://marcan.st/marcan.asc