linux-kernel - [PATCH v2 5/5] selftests/ima: loading kernel modules

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Date:   Tue, 26 Feb 2019 18:27:00 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     linux-kselftest@...r.kernel.org, Shuah Khan <shuah@...nel.org>
Cc:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mimi Zohar <zohar@...ux.ibm.com>
Subject: [PATCH v2 5/5] selftests/ima: loading kernel modules

While the appended kernel module signature can be verified, when loading
a kernel module via either the init_module or the finit_module syscall,
verifying the IMA signature requires access to the file descriptor,
which is only available via the finit_module syscall.  As "modprobe"
does not provide a flag allowing the syscall - init_module or
finit_module - to be specified, this patch does not load a kernel
module.

This test simply verifies that on secure boot enabled systems with
"CONFIG_IMA_ARCH_POLICY" configured, that at least an appended kernel
module signature or an IMA signature is required based on the Kconfig
and the runtime IMA policy.

Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
---
 tools/testing/selftests/ima/Makefile              |  2 +-
 tools/testing/selftests/ima/test_kernel_module.sh | 96 +++++++++++++++++++++++
 2 files changed, 97 insertions(+), 1 deletion(-)
 create mode 100755 tools/testing/selftests/ima/test_kernel_module.sh

diff --git a/tools/testing/selftests/ima/Makefile b/tools/testing/selftests/ima/Makefile
index 049c83c9426c..ef5201ff0bea 100644
--- a/tools/testing/selftests/ima/Makefile
+++ b/tools/testing/selftests/ima/Makefile
@@ -4,7 +4,7 @@ uname_M := $(shell uname -m 2>/dev/null || echo not)
 ARCH ?= $(shell echo $(uname_M) | sed -e s/i.86/x86/ -e s/x86_64/x86/)
 
 ifeq ($(ARCH),x86)
-TEST_PROGS := test_kexec_load.sh test_kexec_file_load.sh
+TEST_PROGS := test_kexec_load.sh test_kexec_file_load.sh test_kernel_module.sh
 TEST_FILES := common_lib.sh
 
 include ../lib.mk
diff --git a/tools/testing/selftests/ima/test_kernel_module.sh b/tools/testing/selftests/ima/test_kernel_module.sh
new file mode 100755
index 000000000000..4009e1b60b03
--- /dev/null
+++ b/tools/testing/selftests/ima/test_kernel_module.sh
@@ -0,0 +1,96 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# On secure boot enabled systems with "CONFIG_IMA_ARCH_POLICY" configured,
+# this test verifies that at least an appended kernel module signature or
+# an IMA signature is required.  It does not attempt to load a kernel module.
+
+TEST="KERNEL_MODULE"
+. ./common_lib.sh
+
+trap "{ rm -f $IKCONFIG ; }" EXIT
+
+# Some of the IMA builtin policies may require the kernel modules to
+# be signed, but these policy rules may be replaced with a custom
+# policy.  Only CONFIG_IMA_APPRAISE_REQUIRE_MODULE_SIGS persists after
+# loading a custom policy.  Check if it is enabled, before reading the
+# IMA runtime sysfs policy file.
+# Return 1 for IMA signature required and 0 for not required.
+is_ima_sig_required()
+{
+	local ret=0
+
+	kconfig_enabled "CONFIG_IMA_APPRAISE_REQUIRE_MODULE_SIGS=y" \
+		"IMA kernel module signature required"
+	if [ $? -eq 1 ]; then
+		log_info "IMA kernel module signature required"
+		return 1
+	fi
+
+	# The architecture specific or a custom policy may require the
+	# kernel module to be signed.  Policy rules are walked sequentially.
+	# As a result, a policy rule may be defined, but might not necessarily
+	# be used.  This test assumes if a policy rule is specified, that is
+	# the intent.
+	if [ $ima_read_policy -eq 1 ]; then
+		check_ima_policy "appraise" "func=MODULE_CHECK" \
+			"appraise_type=imasig"
+		ret=$?
+		[ $ret -eq 1 ] && log_info "IMA signature required";
+	fi
+	return $ret
+}
+
+# loading kernel modules requires root privileges
+if [ $(id -ru) -ne 0 ]; then
+	log_skip "requires root privileges"
+fi
+
+# Are appended signatures required?
+if [ -e /sys/module/module/parameters/sig_enforce ]; then
+	sig_enforce=$(cat /sys/module/module/parameters/sig_enforce)
+	if [ $sig_enforce = "Y" ]; then
+		log_pass "appended kernel module signature required"
+	fi
+fi
+
+get_secureboot_mode
+if [ $? -eq 0 ]; then
+	log_skip "secure boot not enabled"
+fi
+
+# get the kernel config
+get_kconfig
+
+# Determine which kernel config options are enabled
+kconfig_enabled "CONFIG_IMA_ARCH_POLICY=y" \
+	"architecture specific policy enabled"
+arch_policy=$?
+
+kconfig_enabled "CONFIG_MODULE_SIG=y" \
+	"appended kernel modules signature enabled"
+appended_sig_enabled=$?
+
+kconfig_enabled "CONFIG_IMA_READ_POLICY=y" "reading IMA policy permitted"
+ima_read_policy=$?
+
+is_ima_sig_required
+ima_sig_required=$?
+
+if [ $arch_policy -eq 0 ]; then
+	log_skip "architecture specific policy not enabled"
+fi
+
+if [ $appended_sig_enabled -eq 1 ]; then
+	log_fail "appended kernel module signature enabled, but not required"
+fi
+
+if [ $ima_sig_required -eq 1 ]; then
+	log_pass "IMA kernel module signature required"
+fi
+
+if [ $ima_read_policy -eq 1 ]; then
+	log_fail "IMA kernel module signature not required"
+else
+	log_skip "reading IMA policy not permitted"
+fi
-- 
2.7.5