linux-kernel - Re: [RFC PATCH v1] fw_lockdown: new micro LSM module to prevent loading unsigned firmware

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Date:   Fri, 10 Nov 2017 23:39:30 +0100
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:     David Howells <dhowells@...hat.com>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "AKASHI, Takahiro" <takahiro.akashi@...aro.org>,
        Johannes Berg <johannes@...solutions.net>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [RFC PATCH v1] fw_lockdown: new micro LSM module to prevent
 loading unsigned firmware

On Fri, Nov 10, 2017 at 04:02:55PM -0500, Mimi Zohar wrote:
> If the kernel is locked down and IMA-appraisal is not enabled, prevent
> loading of unsigned firmware.
> 
> Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
> ---
> 
> Changelog v1:
> - Lots of minor changes Kconfig, Makefile, fw_lsm.c for such a small patch

<-- snip -->

> diff --git a/security/fw_lockdown/fw_lsm.c b/security/fw_lockdown/fw_lsm.c
> new file mode 100644
> index 000000000000..cce03a5c5280
> --- /dev/null
> +++ b/security/fw_lockdown/fw_lsm.c
> @@ -0,0 +1,51 @@
> +/*
> + * fw_lockdown security module
> + *
> + * Copyright (C) 2017 IBM Corporation
> + *
> + * Authors:
> + * Mimi Zohar <zohar@...ux.vnet.ibm.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + */
> +
> +#define pr_fmt(fmt) "fw_lockdown: " fmt
> +
> +#include <linux/module.h>
> +#include <linux/ima.h>
> +#include <linux/lsm_hooks.h>
> +
> +/**
> + * fw_lockdown_read_file - prevent loading of unsigned firmware
> + * @file: pointer to firmware
> + * @read_id: caller identifier
> + *
> + * Prevent loading of unsigned firmware in lockdown mode.
> + */
> +static int fw_lockdown_read_file(struct file *file, enum kernel_read_file_id id)
> +{
> +	if (id == READING_FIRMWARE) {
> +		if (!is_ima_appraise_enabled() &&
> +		    !kernel_is_locked_down("Loading of unsigned firmware"))
> +			return -EACCES;

I don't have kernel_is_locked_down() but I found it here:

https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/commit/?h=keys-lockdown&id=0ff5adf1e81135c4ed914d0a8b70124caed04142

1) I don't see it taking any arguments
2) Don't we want:

	if (!is_ima_appraise_enabled() && kernel_is_locked_down())
		return -EACCES;

If, only if IMA appraisal is enabled would we enable kernel lockdown.

  Luis