Kconfig hardened check
Motivation
There are plenty of Linux kernel hardening config options. A lot of them are not enabled by the major distros. We have to enable these options ourselves to make our systems more secure.
But nobody likes checking configs manually. So let the computers do their job!
kconfig-hardened-check.py helps me to check the Linux kernel Kconfig option list against my hardening preferences, which are based on the KSPP recommended settings and last public grsecurity patch (options which they disable).
Please don't cry if my Python code looks like C. I'm just a kernel developer.
Supported microarchitectures
- X86_64
- X86_32
- ARM64
- ARM
Script output examples
Usage
#usage: kconfig-hardened-check.py [-h] [-p {X86_64,X86_32,ARM64,ARM}]
[-c CONFIG] [--debug]
Checks the hardening options in the Linux kernel config
optional arguments:
-h, --help show this help message and exit
-p {X86_64,X86_32,ARM64,ARM}, --print {X86_64,X86_32,ARM64,ARM}
print hardening preferences for selected architecture
-c CONFIG, --config CONFIG
check the config_file against these preferences
--debug enable internal debug mode
Script output for Ubuntu 18.04 (Bionic Beaver) kernel config
#./kconfig-hardened-check.py -c config_files/distros/ubuntu-bionic-generic.config
[+] Trying to detect architecture in "config_files/distros/ubuntu-bionic-generic.config"...
[+] Detected architecture: X86_64
[+] Checking "config_files/distros/ubuntu-bionic-generic.config" against hardening preferences...
option name | desired val | decision | reason || check result
===================================================================================================================
CONFIG_BUG | y |defconfig | self_protection || OK
CONFIG_STRICT_KERNEL_RWX | y |defconfig | self_protection || OK
CONFIG_STACKPROTECTOR_STRONG | y |defconfig | self_protection ||OK: CONFIG_CC_STACKPROTECTOR_STRONG "y"
CONFIG_SLUB_DEBUG | y |defconfig | self_protection || OK
CONFIG_STRICT_MODULE_RWX | y |defconfig | self_protection || OK
CONFIG_PAGE_TABLE_ISOLATION | y |defconfig | self_protection || OK
CONFIG_RANDOMIZE_MEMORY | y |defconfig | self_protection || OK
CONFIG_RANDOMIZE_BASE | y |defconfig | self_protection || OK
CONFIG_RETPOLINE | y |defconfig | self_protection || OK
CONFIG_X86_SMAP | y |defconfig | self_protection || OK
CONFIG_X86_INTEL_UMIP | y |defconfig | self_protection || OK
CONFIG_SYN_COOKIES | y |defconfig | self_protection || OK
CONFIG_VMAP_STACK | y |defconfig | self_protection || OK
CONFIG_THREAD_INFO_IN_TASK | y |defconfig | self_protection || OK
CONFIG_BUG_ON_DATA_CORRUPTION | y | kspp | self_protection || FAIL: "is not set"
CONFIG_DEBUG_WX | y | kspp | self_protection || OK
CONFIG_SCHED_STACK_END_CHECK | y | kspp | self_protection || OK
CONFIG_SLAB_FREELIST_HARDENED | y | kspp | self_protection || OK
CONFIG_SLAB_FREELIST_RANDOM | y | kspp | self_protection || OK
CONFIG_FORTIFY_SOURCE | y | kspp | self_protection || OK
CONFIG_GCC_PLUGINS | y | kspp | self_protection || FAIL: "is not set"
CONFIG_GCC_PLUGIN_RANDSTRUCT | y | kspp | self_protection || FAIL: not found
CONFIG_GCC_PLUGIN_STRUCTLEAK | y | kspp | self_protection || FAIL: not found
CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL | y | kspp | self_protection || FAIL: not found
CONFIG_GCC_PLUGIN_LATENT_ENTROPY | y | kspp | self_protection || FAIL: not found
CONFIG_DEBUG_LIST | y | kspp | self_protection || FAIL: "is not set"
CONFIG_DEBUG_SG | y | kspp | self_protection || FAIL: "is not set"
CONFIG_DEBUG_CREDENTIALS | y | kspp | self_protection || FAIL: "is not set"
CONFIG_DEBUG_NOTIFIERS | y | kspp | self_protection || FAIL: "is not set"
CONFIG_PAGE_POISONING | y | kspp | self_protection || FAIL: "is not set"
CONFIG_HARDENED_USERCOPY | y | kspp | self_protection || OK
CONFIG_HARDENED_USERCOPY_FALLBACK | is not set | kspp | self_protection || OK: not found
CONFIG_MODULE_SIG | y | kspp | self_protection || OK
CONFIG_MODULE_SIG_ALL | y | kspp | self_protection || OK
CONFIG_MODULE_SIG_SHA512 | y | kspp | self_protection || OK
CONFIG_MODULE_SIG_FORCE | y | kspp | self_protection || FAIL: "is not set"
CONFIG_DEFAULT_MMAP_MIN_ADDR | 65536 | kspp | self_protection || OK
CONFIG_REFCOUNT_FULL | y | kspp | self_protection || FAIL: "is not set"
CONFIG_GCC_PLUGIN_STACKLEAK | y | my | self_protection || FAIL: not found
CONFIG_LOCK_DOWN_KERNEL | y | my | self_protection || OK
CONFIG_SLUB_DEBUG_ON | y | my | self_protection || FAIL: "is not set"
CONFIG_SECURITY_DMESG_RESTRICT | y | my | self_protection || FAIL: "is not set"
CONFIG_STATIC_USERMODEHELPER | y | my | self_protection || FAIL: "is not set"
CONFIG_SECURITY_LOADPIN | y | my | self_protection || FAIL: "is not set"
CONFIG_RESET_ATTACK_MITIGATION | y | my | self_protection || OK
CONFIG_SLAB_MERGE_DEFAULT | is not set | my | self_protection || FAIL: "y"
CONFIG_PAGE_POISONING_NO_SANITY | is not set | my | self_protection ||FAIL: CONFIG_PAGE_POISONING is needed
CONFIG_PAGE_POISONING_ZERO | is not set | my | self_protection ||FAIL: CONFIG_PAGE_POISONING is needed
CONFIG_SECURITY | y |defconfig | security_policy || OK
CONFIG_SECURITY_YAMA | y | kspp | security_policy || OK
CONFIG_SECURITY_SELINUX_DISABLE | is not set | kspp | security_policy || OK
CONFIG_SECCOMP | y |defconfig | cut_attack_surface || OK
CONFIG_SECCOMP_FILTER | y |defconfig | cut_attack_surface || OK
CONFIG_STRICT_DEVMEM | y |defconfig | cut_attack_surface || OK
CONFIG_MODULES | is not set | kspp | cut_attack_surface || FAIL: "y"
CONFIG_DEVMEM | is not set | kspp | cut_attack_surface || FAIL: "y"
CONFIG_IO_STRICT_DEVMEM | y | kspp | cut_attack_surface || FAIL: "is not set"
CONFIG_ACPI_CUSTOM_METHOD | is not set | kspp | cut_attack_surface || OK
CONFIG_COMPAT_BRK | is not set | kspp | cut_attack_surface || OK
CONFIG_DEVKMEM | is not set | kspp | cut_attack_surface || OK
CONFIG_COMPAT_VDSO | is not set | kspp | cut_attack_surface || OK
CONFIG_BINFMT_MISC | is not set | kspp | cut_attack_surface || FAIL: "m"
CONFIG_INET_DIAG | is not set | kspp | cut_attack_surface || FAIL: "m"
CONFIG_KEXEC | is not set | kspp | cut_attack_surface || FAIL: "y"
CONFIG_PROC_KCORE | is not set | kspp | cut_attack_surface || FAIL: "y"
CONFIG_LEGACY_PTYS | is not set | kspp | cut_attack_surface || FAIL: "y"
CONFIG_HIBERNATION | is not set | kspp | cut_attack_surface || FAIL: "y"
CONFIG_LEGACY_VSYSCALL_NONE | y | kspp | cut_attack_surface || FAIL: "is not set"
CONFIG_IA32_EMULATION | is not set | kspp | cut_attack_surface || FAIL: "y"
CONFIG_X86_X32 | is not set | kspp | cut_attack_surface || FAIL: "y"
CONFIG_MODIFY_LDT_SYSCALL | is not set | kspp | cut_attack_surface || FAIL: "y"
CONFIG_X86_PTDUMP | is not set |grsecurity| cut_attack_surface || OK
CONFIG_ZSMALLOC_STAT | is not set |grsecurity| cut_attack_surface || OK
CONFIG_PAGE_OWNER | is not set |grsecurity| cut_attack_surface || OK
CONFIG_DEBUG_KMEMLEAK | is not set |grsecurity| cut_attack_surface || OK
CONFIG_BINFMT_AOUT | is not set |grsecurity| cut_attack_surface || OK: not found
CONFIG_KPROBES | is not set |grsecurity| cut_attack_surface || FAIL: "y"
CONFIG_UPROBES | is not set |grsecurity| cut_attack_surface || FAIL: "y"
CONFIG_GENERIC_TRACER | is not set |grsecurity| cut_attack_surface || FAIL: "y"
CONFIG_PROC_VMCORE | is not set |grsecurity| cut_attack_surface || FAIL: "y"
CONFIG_PROC_PAGE_MONITOR | is not set |grsecurity| cut_attack_surface || FAIL: "y"
CONFIG_USELIB | is not set |grsecurity| cut_attack_surface || FAIL: "y"
CONFIG_CHECKPOINT_RESTORE | is not set |grsecurity| cut_attack_surface || FAIL: "y"
CONFIG_USERFAULTFD | is not set |grsecurity| cut_attack_surface || FAIL: "y"
CONFIG_HWPOISON_INJECT | is not set |grsecurity| cut_attack_surface || FAIL: "m"
CONFIG_MEM_SOFT_DIRTY | is not set |grsecurity| cut_attack_surface || FAIL: "y"
CONFIG_DEVPORT | is not set |grsecurity| cut_attack_surface || FAIL: "y"
CONFIG_DEBUG_FS | is not set |grsecurity| cut_attack_surface || FAIL: "y"
CONFIG_NOTIFIER_ERROR_INJECTION | is not set |grsecurity| cut_attack_surface || FAIL: "m"
CONFIG_ACPI_TABLE_UPGRADE | is not set | lockdown | cut_attack_surface || FAIL: "y"
CONFIG_ACPI_APEI_EINJ | is not set | lockdown | cut_attack_surface || FAIL: "m"
CONFIG_PROFILING | is not set | lockdown | cut_attack_surface || FAIL: "y"
CONFIG_BPF_SYSCALL | is not set | lockdown | cut_attack_surface || FAIL: "y"
CONFIG_MMIOTRACE_TEST | is not set | lockdown | cut_attack_surface || OK
CONFIG_MMIOTRACE | is not set | my | cut_attack_surface || FAIL: "y"
CONFIG_KEXEC_FILE | is not set | my | cut_attack_surface || FAIL: "y"
CONFIG_LIVEPATCH | is not set | my | cut_attack_surface || FAIL: "y"
CONFIG_USER_NS | is not set | my | cut_attack_surface || FAIL: "y"
CONFIG_IP_DCCP | is not set | my | cut_attack_surface || FAIL: "m"
CONFIG_IP_SCTP | is not set | my | cut_attack_surface || FAIL: "m"
CONFIG_FTRACE | is not set | my | cut_attack_surface || FAIL: "y"
CONFIG_BPF_JIT | is not set | my | cut_attack_surface || FAIL: "y"
CONFIG_ARCH_MMAP_RND_BITS | 32 | my |userspace_protection|| FAIL: "28"
[+] config check is finished: 'OK' - 43 / 'FAIL' - 60
Questions and answers
Q: How disabling CONFIG_USER_NS cuts the attack surface? It's needed for containers!
A: Yes, the CONFIG_USER_NS option provides some isolation between the userspace programs,
but the script recommends disabling it to cut the attack surface of the kernel.
The rationale:
-
A nice LWN article about the corresponding LKML discussion: https://lwn.net/Articles/673597/
-
A twitter thread about
CONFIG_USER_NSand security: https://twitter.com/robertswiecki/status/1095447678949953541
Q: Why CONFIG_GCC_PLUGINS is automatically disabled during the kernel compilation?
A: It means that your gcc doesn't support plugins. For example, if you have gcc-7 on Ubuntu,
try to install gcc-7-plugin-dev package, it should help.