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

Mimi Zohar
2017-11-10T17:58:33Z

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@linux.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@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/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