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

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Date:   Fri, 10 Nov 2017 12:58:23 -0500
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-security-module <linux-security-module@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Luis R. Rodriguez" <mcgrof@...e.com>,
        "AKASHI, Takahiro" <takahiro.akashi@...aro.org>
Subject: [RFC PATCH] fw_lockdown: new micro LSM module to prevent loading
 unsigned firmware

Hi David,

If you are interested in preventing the loading of unsigned firmware,
the patch below is straight forward.  The patch has ONLY been tested
with IMA-appraisal enabled, and works as intended - allowing only
signed firmware to be loaded.

Mimi
---

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>
---
 security/Kconfig                   |  1 +
 security/Makefile                  |  2 ++
 security/fw_lockdown/Kconfig       |  6 +++++
 security/fw_lockdown/Makefile      |  3 +++
 security/fw_lockdown/fw_lockdown.c | 52 ++++++++++++++++++++++++++++++++++++++
 5 files changed, 64 insertions(+)
 create mode 100644 security/fw_lockdown/Kconfig
 create mode 100644 security/fw_lockdown/Makefile
 create mode 100644 security/fw_lockdown/fw_lockdown.c

diff --git a/security/Kconfig b/security/Kconfig
index a4fa8b826039..6e7e5888f823 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -243,6 +243,7 @@ source security/tomoyo/Kconfig
 source security/apparmor/Kconfig
 source security/loadpin/Kconfig
 source security/yama/Kconfig
+source security/fw_lockdown/Kconfig
 
 source security/integrity/Kconfig
 
diff --git a/security/Makefile b/security/Makefile
index 8c4a43e3d4e0..58852dee5e22 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -9,6 +9,7 @@ subdir-$(CONFIG_SECURITY_TOMOYO)        += tomoyo
 subdir-$(CONFIG_SECURITY_APPARMOR)	+= apparmor
 subdir-$(CONFIG_SECURITY_YAMA)		+= yama
 subdir-$(CONFIG_SECURITY_LOADPIN)	+= loadpin
+subdir-$(CONFIG_SECURITY_FW_LOCKDOWN)	+= fw_lockdown
 
 # always enable default capabilities
 obj-y					+= commoncap.o
@@ -24,6 +25,7 @@ obj-$(CONFIG_SECURITY_TOMOYO)		+= tomoyo/
 obj-$(CONFIG_SECURITY_APPARMOR)		+= apparmor/
 obj-$(CONFIG_SECURITY_YAMA)		+= yama/
 obj-$(CONFIG_SECURITY_LOADPIN)		+= loadpin/
+obj-$(CONFIG_SECURITY_FW_LOCKDOWN)	+= fw_lockdown/
 obj-$(CONFIG_CGROUP_DEVICE)		+= device_cgroup.o
 
 # Object integrity file lists
diff --git a/security/fw_lockdown/Kconfig b/security/fw_lockdown/Kconfig
new file mode 100644
index 000000000000..cb7780f7c7f5
--- /dev/null
+++ b/security/fw_lockdown/Kconfig
@@ -0,0 +1,6 @@
+config SECURITY_FW_LOCKDOWN
+	bool "Prevent loading unsigned firmware"
+	depends on SECURITY && CONFIG_LOCK_DOWN_KERNEL
+	default y
+	help
+	  Prevent loading unsigned firmware in lockdown mode,
diff --git a/security/fw_lockdown/Makefile b/security/fw_lockdown/Makefile
new file mode 100644
index 000000000000..9798a396d4ef
--- /dev/null
+++ b/security/fw_lockdown/Makefile
@@ -0,0 +1,3 @@
+obj-$(CONFIG_SECURITY_FW_LOCKDOWN) += fw_lockdown.o
+
+fw_lockdown-y := fw_lockdown.o
diff --git a/security/fw_lockdown/fw_lockdown.c b/security/fw_lockdown/fw_lockdown.c
new file mode 100644
index 000000000000..15dd6b353eea
--- /dev/null
+++ b/security/fw_lockdown/fw_lockdown.c
@@ -0,0 +1,52 @@
+/*
+ * 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/binfmts.h>
+#include <linux/namei.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 (read_id == READING_FIRMWARE) {
+		if (!is_ima_appraise_enabled() &&
+		    kernel_is_locked_down("Loading of unsigned firmware"))
+			return -EACCES;
+	}
+	return 0;
+}
+
+static struct security_hook_list fw_lockdown_hooks[] = {
+	LSM_HOOK_INIT(fw_lockdown_file_check, fw_lockdown_bprm_check)
+};
+
+static int __init init_fw_lockdown(void)
+{
+	security_add_hooks(fw_lockdown_hooks, ARRAY_SIZE(fw_lockdown_hooks),
+			   "fw_lockdown");
+	pr_info("initialized\n");
+	return 0;
+}
+
+late_initcall(init_fw_lockdown);
+MODULE_LICENSE("GPL");
-- 
2.7.4