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

On Fri, 2017-11-10 at 23:39 +0100, Luis R. Rodriguez wrote:

On Fri, Nov 10, 2017 at 04:02:55PM -0500, Mimi Zohar wrote:

quoted

If the kernel is locked down and IMA-appraisal is not enabled, prevent
loading of unsigned firmware.

Signed-off-by: Mimi Zohar <redacted>
---

Changelog v1:
- Lots of minor changes Kconfig, Makefile, fw_lsm.c for such a small patch

<-- snip -->

quoted

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@linux.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

David reposted the patches?https://lkml.org/lkml/2017/11/9/659?with
the change. ?The latest version of the patches are in his?efi-lock-
down branch.

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.

Yes, the kernel_is_locked_down() test needs to be inverted.

Mimi

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