Re: [PATCH 3/3] selftests/ima: kexec_file_load syscall test

Petr Vorel
2019-02-03T22:03:05Z

Hi Mimi,

> The kernel can be configured to verify PE signed kernel images, IMA
> kernel image signatures, both types of signatures, or none. This test
> verifies only properly signed kernel images are loaded into memory,
> based on the kernel configuration and runtime policies.

> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Petr Vorel <pvorel@suse.cz>

...
> +++ b/tools/testing/selftests/ima/test_kexec_file_load.sh
> @@ -0,0 +1,250 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0+
# SPDX-License-Identifier: GPL-2.0-or-later
> +#
> +# Loading a kernel image via the kexec_file_load syscall can verify either
> +# the IMA signature stored in the security.ima xattr or the PE signature,
> +# both signatures depending on the IMA policy, or none.
> +#
> +# To determine whether the kernel image is signed, this test depends
> +# on pesign and getfattr. This test also requires the kernel to be
> +# built with CONFIG_IKCONFIG enabled and either CONFIG_IKCONFIG_PROC
> +# enabled or access to the extract-ikconfig script.
> +
> +VERBOSE=1
Maybe allow to disable verbose without source change?
VERBOSE="${VERBOSE:-1}"

> +EXTRACT_IKCONFIG=$(ls /lib/modules/`uname -r`/source/scripts/extract-ikconfig)
> +IKCONFIG=/tmp/config-`uname -r`
> +PROC_CONFIG="/proc/config.gz"
> +KERNEL_IMAGE="/boot/vmlinuz-`uname -r`"
> +PESIGN=/usr/bin/pesign
> +GETFATTR=/usr/bin/getfattr
> +
> +TEST="$0"
> +. ./common_lib.sh
> +
> +# Kselftest framework requirement - SKIP code is 4.
> +ksft_skip=4
> +
> +kconfig_enabled()
> +{
> + RC=0
> + egrep -q $1 $IKCONFIG
> + if [ $? -eq 0 ]; then
> + RC=1
> + fi
> + return $RC
> +}
This would be enough (grep with -e returns only 0 or 1):
kconfig_enabled()
{
grep -E -q $1 $IKCONFIG
}
> +
> +# policy rule format: action func=<keyword> [appraise_type=<type>]
> +check_ima_policy()
> +{
> + IMA_POLICY=/sys/kernel/security/ima/policy
> +
> + RC=0
> + if [ $# -eq 3 ]; then
> + grep -e $2 $IMA_POLICY | grep -e "^$1.*$3" 2>&1 >/dev/null
> + else
> + grep -e $2 $IMA_POLICY | grep -e "^$1" 2>&1 >/dev/null
> + fi
> + if [ $? -eq 0 ]; then
> + RC=1
> + fi
> + return $RC
> +}
This would be enough and more descriptive:
check_ima_policy()
{
local action="$1"
local keyword="$2"
local type="$3"

[ -n "$type" ] && type="appraise_type=$type"
grep -q "^$action.*func=$keyword.*$type" /sys/kernel/security/ima/policy
}

> +
> +check_kconfig_options()
> +{
> + # Attempt to get the kernel config first via proc, and then by
> + # extracting it from the kernel image using scripts/extract-ikconfig.
> + if [ ! -f $PROC_CONFIG ]; then
> + modprobe configs 2>/dev/null
> + fi
> + if [ -f $PROC_CONFIG ]; then
> + cat $PROC_CONFIG > $IKCONFIG
> + fi
> +
> + if [ ! -f $IKCONFIG ]; then
> + if [ ! -f $EXTRACT_IKCONFIG ]; then
> + echo "$TEST: requires access to extract-ikconfig" >&2
> + exit $ksft_skip
> + fi
> +
> + $EXTRACT_IKCONFIG $KERNEL_IMAGE > $IKCONFIG
> + kconfig_enabled "CONFIG_IKCONFIG=y"
> + if [ $? -eq 0 ]; then
> + echo "$TEST: requires the kernel to be built with CONFIG_IKCONFIG" >&2
> + exit $ksft_skip
> + fi
> + fi
> +
> + kconfig_enabled "CONFIG_KEXEC_BZIMAGE_VERIFY_SIG=y"
> + pe_sig_required=$?
> + if [ $VERBOSE -ne 0 ] && [ $pe_sig_required -eq 1 ]; then
> + echo "$TEST: [INFO] PE signed kernel image required"
> + fi
Checks for $VERBOSE here and in other kconfig_enabled usages bellow are a bit
redundant. And you check for assigned variable now and then later on,
you use these variables as global (and reset $ima_sig_required in
check_runtime().

How about using functions instead:
log_info()
{
echo "$TEST: [INFO] $1"
}
(Reducing some duplicity, IMHO helper functions in shell library used in all
selftest tests would be useful)

kconfig_enabled()
{
local config="$1"
local msg="$2"
local ret

grep -E -q $config $IKCONFIG
ret=$?
[ $VERBOSE -ne 0 ] && [ $ret -eq 1 ] && log_info "$msg"
return $ret
}

ima_sig_enabled()
{
kconfig_enabled "CONFIG_KEXEC_BZIMAGE_VERIFY_SIG=y" \
"PE signed kernel image required"
}

ima_sig_enabled()
{
kconfig_enabled "CONFIG_IMA_APPRAISE_REQUIRE_KEXEC_SIGS=y" \
"IMA kernel image signature required"
}
Warning is printed each time, but that's deliberate.
If it's not wanted, it can be moved into setup.

...
> +check_kconfig_options
> +check_for_apps
> +check_runtime
> +check_for_sigs
> +kexec_file_load_test

> +rc=$?
> +exit $rc
These two are redundant.

Kind regards,
Petr