[PATCH 4/7] evmtest: test kexec signature policy

[David Jacobson]

With secure boot enabled, the bootloader verifies the kernel image's
signature before transferring control to it. With Linux as the
bootloader running with secure boot enabled, kexec needs to verify the
kernel image's signature.

This patch defined a new test named "kexec_sig", which first attempts to
kexec an unsigned kernel image with an IMA policy that requires
signatures on any kernel image. Then, the test attempts to kexec the
signed kernel image, which should succeed.

Signed-off-by: David Jacobson <davidj@xxxxxxxxxxxxx>
---
 evmtest/files/policies/kexec_policy |   3 +
 evmtest/functions/r_kexec_sig.sh    | 156 ++++++++++++++++++++++++++++
 2 files changed, 159 insertions(+)
 create mode 100644 evmtest/files/policies/kexec_policy
 create mode 100755 evmtest/functions/r_kexec_sig.sh

diff --git a/evmtest/files/policies/kexec_policy b/evmtest/files/policies/kexec_policy
new file mode 100644
index 0000000..dc00fa7
--- /dev/null
+++ b/evmtest/files/policies/kexec_policy
@@ -0,0 +1,3 @@
+appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig
+measure func=KEXEC_KERNEL_CHECK
+audit func=KEXEC_KERNEL_CHECK
diff --git a/evmtest/functions/r_kexec_sig.sh b/evmtest/functions/r_kexec_sig.sh
new file mode 100755
index 0000000..e1295b9
--- /dev/null
+++ b/evmtest/functions/r_kexec_sig.sh
@@ -0,0 +1,156 @@
+#!/bin/bash
+# Author: David Jacobson <davidj@xxxxxxxxxxxxx>
+TEST="r_kexec_sig"
+ROOT="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null && pwd )/.."
+source $ROOT/files/common.sh
+VERBOSE=0
+POLICY_LOAD=$ROOT/files/load_policy.sh
+
+# This test validates that IMA measures and appraises signatures on kernel
+# images when trying to kexec, if the current policy requires that.
+usage() {
+	echo ""
+	echo "kexec_sig -k <key> [-i <kernel_image]"
+	echo "	[-vh]"
+	echo ""
+	echo "	This test must be run as root"
+	echo "	Note: kexec may require PECOFF signature"
+	echo ""
+	echo "	This test will check that IMA prevents kexec-ing to "
+	echo "	unsigned kernel image."
+	echo ""
+	echo "	-k,--key	The key for the certificate on the IMA keyring"
+	echo "	-i,--image	An unsigned kernel image"
+	echo "	-h,--help	Display this help message"
+	echo "	-v,--verbose	Verbose logging"
+}
+
+TEMP=`getopt -o 'k:i:hv' -l 'key:,image:,help,verbose' -n 'r_kexec_sig' -- "$@"`
+eval set -- "$TEMP"
+
+while true ; do
+	case "$1" in
+	-h|--help) usage; exit 0 ; shift;;
+	-i|--image) KERNEL_IMAGE=$2; shift 2;;
+	-k|--key) IMA_KEY=$2; shift 2;;
+	-v|--verbose) VERBOSE=1; shift;;
+	--) shift; break;;
+	*) echo "[*] Unrecognized option $1"; exit 1;;
+	esac
+done
+
+if [[ -z $IMA_KEY ]]; then
+	usage
+	exit 1
+else
+	if [[ ! -e $IMA_KEY ]]; then
+		fail "Please provide valid keys"
+	fi
+fi
+
+# If the user doesn't provide a kernel image for kexec, get the current
+if [[ -z $KERNEL_IMAGE ]]; then
+	v_out "No kernel provided, looking for running kernel"
+	RUNNING_KERNEL=`uname -r`
+	if [[ -e /boot/vmlinuz-$RUNNING_KERNEL ]]; then
+		KERNEL_IMAGE=/boot/vmlinuz-$RUNNING_KERNEL
+		TEMP_LOCATION=`mktemp`
+		v_out "Found kernel in: $KERNEL_IMAGE"
+		v_out "Copying kernel to $TEMP_LOCATION"
+		cp $KERNEL_IMAGE $TEMP_LOCATION
+		KERNEL_IMAGE=$TEMP_LOCATION
+	fi
+else
+	# If a kernel has been provided, ensure it exists
+	if [[ ! -e $KERNEL_IMAGE ]]; then
+		fail "Kernel image not found..."
+	else
+		v_out "Valid Kernel provided, continuing"
+	fi
+fi
+
+EVMTEST_require_root
+
+begin
+
+v_out "Writing file hash on kernel image"
+evmctl ima_hash -a sha256 -f $KERNEL_IMAGE
+
+
+v_out "Attempting to sign policy..."
+evmctl ima_sign -f $ROOT/files/policies/kexec_policy -k $IMA_KEY
+
+v_out "Loading kexec policy..."
+$POLICY_LOAD kexec_policy &>> /dev/null
+
+if [[ $? != 0 ]]; then
+	fail "Could not update policy - verify keys"
+fi
+
+v_out "Testing kexec (using kexec_file_load) on unsigned image..."
+# -s uses the kexec_file_load syscall
+kexec -s -l $KERNEL_IMAGE &>> /dev/null
+loaded_unsigned=$?
+if [[ $loaded_unsigned != 0 ]]; then # Permission denied (IMA)
+	v_out "Correctly prevented kexec of an unsigned image"
+else
+	kexec -s -u
+	fail "kexec loaded instead of rejecting. Unloading and exiting."
+fi
+
+v_out "Testing kexec (using kexec_load) on unsigned image..."
+kexec -l $KERNEL_IMAGE &>> /dev/null
+if [[ $? == 0 ]]; then
+	kexec -u
+	fail "Kexec loaded unsigned image - unloading"
+else
+	v_out "Correctly prevented kexec of an unsigned image"
+fi
+
+# On some systems this prevents resigning the kernel image
+
+#v_out "Signing image with invalid key..."
+#evmctl ima_sign -f $KERNEL_IMAGE -k $ROOT/files/bad_privkey_ima.pem
+#kexec -s -l $KERNEL_IMAGE &>> /dev/null
+#loaded_bad_signature=$?
+
+#if [[ $loaded_bad_signature == 0 ]]; then
+#	kexec -u
+#	fail "Kernel image signed by invalid party was allowed to load.\
+#		Unloaded"
+#fi
+
+#v_out "Correctly prevented loading of kernel signed by unknown key"
+
+v_out "Signing kernel image with provided key..."
+evmctl ima_sign -f $KERNEL_IMAGE -k $IMA_KEY
+
+v_out "Attempting to kexec signed image using kexec_file_load..."
+kexec -s -l $KERNEL_IMAGE &>> /dev/null
+
+loaded_signed=$?
+if [[ $loaded_signed != 0 ]]; then
+	fail "kexec rejected a signed image - possibly due to PECOFF signature"
+else
+	v_out "kexec correctly loaded signed image...unloading"
+fi
+
+kexec -s -u
+
+v_out "Attempting kexec_load on signed kernel... [should fail]"
+kexec -l $KERNEL_IMAGE &>> /dev/null
+
+if [[ $? == 0 ]]; then
+	kexec -u
+	fail "Signed image was allowed to load without file descriptor for\
+		appraisal. Unloading."
+fi
+
+v_out "Correctly prevented loading"
+
+v_out "Cleaning up..."
+if [[ ! -z $TEMP_LOCATION ]]; then
+	rm $TEMP_LOCATION
+fi
+
+passed
-- 
2.17.1