# kconfig-hardened-check ![functional test](https://github.com/a13xp0p0v/kconfig-hardened-check/workflows/functional%20test/badge.svg) [![Coverage Status](https://codecov.io/gh/a13xp0p0v/kconfig-hardened-check/graph/badge.svg)](https://codecov.io/gh/a13xp0p0v/kconfig-hardened-check) ## Motivation There are plenty of security hardening options in the Linux kernel. 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 security hardening preferences, which are based on the - [KSPP recommended settings][1], - [CLIP OS kernel configuration][2], - Last public [grsecurity][3] patch (options which they disable), - [SECURITY_LOCKDOWN_LSM][5] patchset, - Direct feedback from Linux kernel maintainers (see [#38][6], [#53][15], [#54][16]). I also created [__Linux Kernel Defence Map__][4] that is a graphical representation of the relationships between security hardening features and the corresponding vulnerability classes or exploitation techniques. ## Supported microarchitectures - X86_64 - X86_32 - ARM64 - ARM TODO: RISC-V ## Installation You can install the package: ``` pip install git+https://github.com/a13xp0p0v/kconfig-hardened-check ``` or simply run `./bin/kconfig-hardened-check` from the cloned repository. Some Linux distributions also provide `kconfig-hardened-check` as a package. ## Usage ``` usage: kconfig-hardened-check [-h] [--version] [-p {X86_64,X86_32,ARM64,ARM}] [-c CONFIG] [-m {verbose,json,show_ok,show_fail}] A tool for checking the security hardening options of the Linux kernel optional arguments: -h, --help show this help message and exit --version show program's version number and exit -p {X86_64,X86_32,ARM64,ARM}, --print {X86_64,X86_32,ARM64,ARM} print security hardening preferences for the selected architecture -c CONFIG, --config CONFIG check the kernel config file against these preferences -m {verbose,json,show_ok,show_fail}, --mode {verbose,json,show_ok,show_fail} choose the report mode ``` ## Output modes - no `-m` argument for the default output mode (see the example below) - `-m verbose` for printing additional info: - config options without a corresponding check - internals of complex checks with AND/OR, like this: ``` ------------------------------------------------------------------------------------------- <<< OR >>> CONFIG_STRICT_DEVMEM | y |defconfig | cut_attack_surface CONFIG_DEVMEM | is not set | kspp | cut_attack_surface ------------------------------------------------------------------------------------------- ``` - `-m show_fail` for showing only the failed checks - `-m show_ok` for showing only the successful checks - `-m json` for printing the results in JSON format (for combining `kconfig-hardened-check` with other tools) ## Example output for `Ubuntu 20.04 LTS (Focal Fossa)` kernel config ``` $ ./bin/kconfig-hardened-check -c kconfig_hardened_check/config_files/distros/ubuntu-focal.config [+] Config file to check: kconfig_hardened_check/config_files/distros/ubuntu-focal.config [+] Detected architecture: X86_64 [+] Detected kernel version: 5.4 ========================================================================================================================= option name | type |desired val | decision | reason | check result ========================================================================================================================= CONFIG_BUG |kconfig| y |defconfig | self_protection | OK CONFIG_SLUB_DEBUG |kconfig| y |defconfig | self_protection | OK CONFIG_GCC_PLUGINS |kconfig| y |defconfig | self_protection | FAIL: not found CONFIG_STACKPROTECTOR_STRONG |kconfig| y |defconfig | self_protection | OK CONFIG_STRICT_KERNEL_RWX |kconfig| y |defconfig | self_protection | OK CONFIG_STRICT_MODULE_RWX |kconfig| y |defconfig | self_protection | OK CONFIG_REFCOUNT_FULL |kconfig| y |defconfig | self_protection | FAIL: "is not set" CONFIG_IOMMU_SUPPORT |kconfig| y |defconfig | self_protection | OK CONFIG_RANDOMIZE_BASE |kconfig| y |defconfig | self_protection | OK CONFIG_THREAD_INFO_IN_TASK |kconfig| y |defconfig | self_protection | OK CONFIG_VMAP_STACK |kconfig| y |defconfig | self_protection | OK CONFIG_MICROCODE |kconfig| y |defconfig | self_protection | OK CONFIG_RETPOLINE |kconfig| y |defconfig | self_protection | OK CONFIG_X86_SMAP |kconfig| y |defconfig | self_protection | OK CONFIG_SYN_COOKIES |kconfig| y |defconfig | self_protection | OK CONFIG_X86_UMIP |kconfig| y |defconfig | self_protection | OK: CONFIG_X86_INTEL_UMIP "y" CONFIG_PAGE_TABLE_ISOLATION |kconfig| y |defconfig | self_protection | OK CONFIG_RANDOMIZE_MEMORY |kconfig| y |defconfig | self_protection | OK CONFIG_INTEL_IOMMU |kconfig| y |defconfig | self_protection | OK CONFIG_AMD_IOMMU |kconfig| y |defconfig | self_protection | OK CONFIG_SECURITY_DMESG_RESTRICT |kconfig| y | kspp | self_protection | FAIL: "is not set" CONFIG_BUG_ON_DATA_CORRUPTION |kconfig| y | kspp | self_protection | FAIL: "is not set" CONFIG_DEBUG_WX |kconfig| y | kspp | self_protection | OK CONFIG_SCHED_STACK_END_CHECK |kconfig| y | kspp | self_protection | OK CONFIG_SLAB_FREELIST_HARDENED |kconfig| y | kspp | self_protection | OK CONFIG_SLAB_FREELIST_RANDOM |kconfig| y | kspp | self_protection | OK CONFIG_SHUFFLE_PAGE_ALLOCATOR |kconfig| y | kspp | self_protection | OK CONFIG_FORTIFY_SOURCE |kconfig| y | kspp | self_protection | OK CONFIG_DEBUG_LIST |kconfig| y | kspp | self_protection | FAIL: "is not set" CONFIG_DEBUG_SG |kconfig| y | kspp | self_protection | FAIL: "is not set" CONFIG_DEBUG_CREDENTIALS |kconfig| y | kspp | self_protection | FAIL: "is not set" CONFIG_DEBUG_NOTIFIERS |kconfig| y | kspp | self_protection | FAIL: "is not set" CONFIG_INIT_ON_ALLOC_DEFAULT_ON |kconfig| y | kspp | self_protection | OK CONFIG_GCC_PLUGIN_LATENT_ENTROPY |kconfig| y | kspp | self_protection | FAIL: not found CONFIG_GCC_PLUGIN_RANDSTRUCT |kconfig| y | kspp | self_protection | FAIL: not found CONFIG_HARDENED_USERCOPY |kconfig| y | kspp | self_protection | OK CONFIG_HARDENED_USERCOPY_FALLBACK |kconfig| is not set | kspp | self_protection | FAIL: "y" CONFIG_HARDENED_USERCOPY_PAGESPAN |kconfig| is not set | kspp | self_protection | OK CONFIG_MODULE_SIG |kconfig| y | kspp | self_protection | OK CONFIG_MODULE_SIG_ALL |kconfig| y | kspp | self_protection | OK CONFIG_MODULE_SIG_SHA512 |kconfig| y | kspp | self_protection | OK CONFIG_MODULE_SIG_FORCE |kconfig| y | kspp | self_protection | FAIL: "is not set" CONFIG_INIT_STACK_ALL_ZERO |kconfig| y | kspp | self_protection | FAIL: not found CONFIG_INIT_ON_FREE_DEFAULT_ON |kconfig| y | kspp | self_protection | OK: CONFIG_PAGE_POISONING_ZERO "y" CONFIG_GCC_PLUGIN_STACKLEAK |kconfig| y | kspp | self_protection | FAIL: not found CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT |kconfig| y | kspp | self_protection | FAIL: not found CONFIG_DEFAULT_MMAP_MIN_ADDR |kconfig| 65536 | kspp | self_protection | OK CONFIG_UBSAN_BOUNDS |kconfig| y |maintainer| self_protection | FAIL: not found CONFIG_UBSAN_SANITIZE_ALL |kconfig| y |maintainer| self_protection | FAIL: CONFIG_UBSAN_BOUNDS not "y" CONFIG_UBSAN_TRAP |kconfig| y |maintainer| self_protection | FAIL: CONFIG_UBSAN_BOUNDS not "y" CONFIG_DEBUG_VIRTUAL |kconfig| y | clipos | self_protection | FAIL: "is not set" CONFIG_STATIC_USERMODEHELPER |kconfig| y | clipos | self_protection | FAIL: "is not set" CONFIG_EFI_DISABLE_PCI_DMA |kconfig| y | clipos | self_protection | FAIL: not found CONFIG_SLAB_MERGE_DEFAULT |kconfig| is not set | clipos | self_protection | FAIL: "y" CONFIG_RANDOM_TRUST_BOOTLOADER |kconfig| is not set | clipos | self_protection | FAIL: "y" CONFIG_RANDOM_TRUST_CPU |kconfig| is not set | clipos | self_protection | FAIL: "y" CONFIG_GCC_PLUGIN_RANDSTRUCT_PERFORMANCE|kconfig| is not set | clipos | self_protection | FAIL: CONFIG_GCC_PLUGIN_RANDSTRUCT not "y" CONFIG_STACKLEAK_METRICS |kconfig| is not set | clipos | self_protection | FAIL: CONFIG_GCC_PLUGIN_STACKLEAK not "y" CONFIG_STACKLEAK_RUNTIME_DISABLE |kconfig| is not set | clipos | self_protection | FAIL: CONFIG_GCC_PLUGIN_STACKLEAK not "y" CONFIG_INTEL_IOMMU_DEFAULT_ON |kconfig| y | clipos | self_protection | FAIL: "is not set" CONFIG_INTEL_IOMMU_SVM |kconfig| y | clipos | self_protection | OK CONFIG_RESET_ATTACK_MITIGATION |kconfig| y | my | self_protection | OK CONFIG_AMD_IOMMU_V2 |kconfig| y | my | self_protection | FAIL: "m" CONFIG_SECURITY |kconfig| y |defconfig | security_policy | OK CONFIG_SECURITY_YAMA |kconfig| y | kspp | security_policy | OK CONFIG_SECURITY_WRITABLE_HOOKS |kconfig| is not set | my | security_policy | OK: not found CONFIG_SECURITY_LOCKDOWN_LSM |kconfig| y | clipos | security_policy | OK CONFIG_SECURITY_LOCKDOWN_LSM_EARLY |kconfig| y | clipos | security_policy | OK CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY|kconfig| y | clipos | security_policy | FAIL: "is not set" CONFIG_SECURITY_SAFESETID |kconfig| y | my | security_policy | OK CONFIG_SECURITY_LOADPIN |kconfig| y | my | security_policy | FAIL: "is not set" CONFIG_SECURITY_LOADPIN_ENFORCE |kconfig| y | my | security_policy | FAIL: CONFIG_SECURITY_LOADPIN not "y" CONFIG_SECCOMP |kconfig| y |defconfig |cut_attack_surface| OK CONFIG_SECCOMP_FILTER |kconfig| y |defconfig |cut_attack_surface| OK CONFIG_STRICT_DEVMEM |kconfig| y |defconfig |cut_attack_surface| OK CONFIG_ACPI_CUSTOM_METHOD |kconfig| is not set | kspp |cut_attack_surface| OK CONFIG_COMPAT_BRK |kconfig| is not set | kspp |cut_attack_surface| OK CONFIG_DEVKMEM |kconfig| is not set | kspp |cut_attack_surface| OK CONFIG_COMPAT_VDSO |kconfig| is not set | kspp |cut_attack_surface| OK CONFIG_BINFMT_MISC |kconfig| is not set | kspp |cut_attack_surface| FAIL: "m" CONFIG_INET_DIAG |kconfig| is not set | kspp |cut_attack_surface| FAIL: "m" CONFIG_KEXEC |kconfig| is not set | kspp |cut_attack_surface| FAIL: "y" CONFIG_PROC_KCORE |kconfig| is not set | kspp |cut_attack_surface| FAIL: "y" CONFIG_LEGACY_PTYS |kconfig| is not set | kspp |cut_attack_surface| FAIL: "y" CONFIG_HIBERNATION |kconfig| is not set | kspp |cut_attack_surface| FAIL: "y" CONFIG_IA32_EMULATION |kconfig| is not set | kspp |cut_attack_surface| FAIL: "y" CONFIG_X86_X32 |kconfig| is not set | kspp |cut_attack_surface| FAIL: "y" CONFIG_MODIFY_LDT_SYSCALL |kconfig| is not set | kspp |cut_attack_surface| FAIL: "y" CONFIG_OABI_COMPAT |kconfig| is not set | kspp |cut_attack_surface| OK: not found CONFIG_MODULES |kconfig| is not set | kspp |cut_attack_surface| FAIL: "y" CONFIG_DEVMEM |kconfig| is not set | kspp |cut_attack_surface| FAIL: "y" CONFIG_IO_STRICT_DEVMEM |kconfig| y | kspp |cut_attack_surface| FAIL: "is not set" CONFIG_LEGACY_VSYSCALL_NONE |kconfig| y | kspp |cut_attack_surface| FAIL: "is not set" CONFIG_ZSMALLOC_STAT |kconfig| is not set | grsec |cut_attack_surface| OK CONFIG_PAGE_OWNER |kconfig| is not set | grsec |cut_attack_surface| OK CONFIG_DEBUG_KMEMLEAK |kconfig| is not set | grsec |cut_attack_surface| OK CONFIG_BINFMT_AOUT |kconfig| is not set | grsec |cut_attack_surface| OK: not found CONFIG_KPROBE_EVENTS |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_UPROBE_EVENTS |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_GENERIC_TRACER |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_FUNCTION_TRACER |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_STACK_TRACER |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_HIST_TRIGGERS |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_BLK_DEV_IO_TRACE |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_PROC_VMCORE |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_PROC_PAGE_MONITOR |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_USELIB |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_CHECKPOINT_RESTORE |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_USERFAULTFD |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_HWPOISON_INJECT |kconfig| is not set | grsec |cut_attack_surface| FAIL: "m" CONFIG_MEM_SOFT_DIRTY |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_DEVPORT |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_DEBUG_FS |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_NOTIFIER_ERROR_INJECTION |kconfig| is not set | grsec |cut_attack_surface| FAIL: "m" CONFIG_FAIL_FUTEX |kconfig| is not set | grsec |cut_attack_surface| OK: not found CONFIG_PUNIT_ATOM_DEBUG |kconfig| is not set | grsec |cut_attack_surface| FAIL: "m" CONFIG_ACPI_CONFIGFS |kconfig| is not set | grsec |cut_attack_surface| FAIL: "m" CONFIG_EDAC_DEBUG |kconfig| is not set | grsec |cut_attack_surface| OK CONFIG_DRM_I915_DEBUG |kconfig| is not set | grsec |cut_attack_surface| OK CONFIG_BCACHE_CLOSURES_DEBUG |kconfig| is not set | grsec |cut_attack_surface| OK CONFIG_DVB_C8SECTPFE |kconfig| is not set | grsec |cut_attack_surface| OK: not found CONFIG_MTD_SLRAM |kconfig| is not set | grsec |cut_attack_surface| FAIL: "m" CONFIG_MTD_PHRAM |kconfig| is not set | grsec |cut_attack_surface| FAIL: "m" CONFIG_IO_URING |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_KCMP |kconfig| is not set | grsec |cut_attack_surface| OK: not found CONFIG_RSEQ |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_LATENCYTOP |kconfig| is not set | grsec |cut_attack_surface| OK CONFIG_KCOV |kconfig| is not set | grsec |cut_attack_surface| OK CONFIG_PROVIDE_OHCI1394_DMA_INIT |kconfig| is not set | grsec |cut_attack_surface| OK CONFIG_SUNRPC_DEBUG |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y" CONFIG_PTDUMP_DEBUGFS |kconfig| is not set | grsec |cut_attack_surface| OK: not found CONFIG_DRM_LEGACY |kconfig| is not set |maintainer|cut_attack_surface| OK CONFIG_FB |kconfig| is not set |maintainer|cut_attack_surface| FAIL: "y" CONFIG_VT |kconfig| is not set |maintainer|cut_attack_surface| FAIL: "y" CONFIG_BLK_DEV_FD |kconfig| is not set |maintainer|cut_attack_surface| FAIL: "m" CONFIG_AIO |kconfig| is not set |grapheneos|cut_attack_surface| FAIL: "y" CONFIG_STAGING |kconfig| is not set | clipos |cut_attack_surface| FAIL: "y" CONFIG_KSM |kconfig| is not set | clipos |cut_attack_surface| FAIL: "y" CONFIG_KALLSYMS |kconfig| is not set | clipos |cut_attack_surface| FAIL: "y" CONFIG_X86_VSYSCALL_EMULATION |kconfig| is not set | clipos |cut_attack_surface| FAIL: "y" CONFIG_MAGIC_SYSRQ |kconfig| is not set | clipos |cut_attack_surface| FAIL: "y" CONFIG_KEXEC_FILE |kconfig| is not set | clipos |cut_attack_surface| FAIL: "y" CONFIG_USER_NS |kconfig| is not set | clipos |cut_attack_surface| FAIL: "y" CONFIG_X86_MSR |kconfig| is not set | clipos |cut_attack_surface| FAIL: "m" CONFIG_X86_CPUID |kconfig| is not set | clipos |cut_attack_surface| FAIL: "m" CONFIG_X86_IOPL_IOPERM |kconfig| is not set | clipos |cut_attack_surface| OK: not found CONFIG_ACPI_TABLE_UPGRADE |kconfig| is not set | clipos |cut_attack_surface| FAIL: "y" CONFIG_EFI_CUSTOM_SSDT_OVERLAYS |kconfig| is not set | clipos |cut_attack_surface| OK: not found CONFIG_LDISC_AUTOLOAD |kconfig| is not set | clipos |cut_attack_surface| FAIL: "y" CONFIG_X86_INTEL_TSX_MODE_OFF |kconfig| y | clipos |cut_attack_surface| OK CONFIG_EFI_TEST |kconfig| is not set | lockdown |cut_attack_surface| FAIL: "m" CONFIG_BPF_SYSCALL |kconfig| is not set | lockdown |cut_attack_surface| FAIL: "y" CONFIG_MMIOTRACE_TEST |kconfig| is not set | lockdown |cut_attack_surface| OK CONFIG_KPROBES |kconfig| is not set | lockdown |cut_attack_surface| FAIL: "y" CONFIG_TRIM_UNUSED_KSYMS |kconfig| y | my |cut_attack_surface| FAIL: not found CONFIG_MMIOTRACE |kconfig| is not set | my |cut_attack_surface| FAIL: "y" CONFIG_LIVEPATCH |kconfig| is not set | my |cut_attack_surface| FAIL: "y" CONFIG_IP_DCCP |kconfig| is not set | my |cut_attack_surface| FAIL: "m" CONFIG_IP_SCTP |kconfig| is not set | my |cut_attack_surface| FAIL: "m" CONFIG_FTRACE |kconfig| is not set | my |cut_attack_surface| FAIL: "y" CONFIG_VIDEO_VIVID |kconfig| is not set | my |cut_attack_surface| FAIL: "m" CONFIG_INPUT_EVBUG |kconfig| is not set | my |cut_attack_surface| FAIL: "m" CONFIG_INTEGRITY |kconfig| y |defconfig | harden_userspace | OK CONFIG_ARCH_MMAP_RND_BITS |kconfig| 32 | clipos | harden_userspace | FAIL: "28" [+] Config check is finished: 'OK' - 68 / 'FAIL' - 96 ``` ## kconfig-hardened-check versioning I usually update the kernel security hardening recommendations after each Linux kernel release. So the version of `kconfig-hardened-check` is associated with the corresponding version of the kernel. The version format is: __[major_number].[kernel_version].[kernel_patchlevel]__ ## 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 tool 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_NS` and security: https://twitter.com/robertswiecki/status/1095447678949953541 - A good overview of the trade-off between having user namespaces enabled, disabled and available only for root: https://github.com/NixOS/nixpkgs/pull/84522#issuecomment-614640601
__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.
__Q:__ KSPP and CLIP OS recommend `CONFIG_PANIC_ON_OOPS=y`. Why doesn't this tool do the same? __A:__ I personally don't support this recommendation because it provides easy denial-of-service attacks for the whole system (kernel oops is not a rare situation). I think having `CONFIG_BUG` is enough here -- if we have a kernel oops in the process context, the offending/attacking process is killed.
__Q:__ What about performance impact of these security hardening options? __A:__ Ike Devolder [@BlackIkeEagle][7] made some performance tests and described the results in [this article][8].
__Q:__ Why enabling `CONFIG_STATIC_USERMODEHELPER` breaks various things in my GNU/Linux system? Do I really need that feature? __A:__ Linux kernel usermode helpers can be used for privilege escalation in kernel exploits ([example 1][9], [example 2][10]). `CONFIG_STATIC_USERMODEHELPER` prevents that method. But it requires the corresponding support in the userspace: see the [example implementation][11] by Tycho Andersen [@tych0][12].
__Q:__ Does my kernel have all those mitigations of Transient Execution Vulnerabilities in my hardware? __A:__ Checking the kernel config is not enough to answer this question. I highly recommend using [spectre-meltdown-checker][13] tool maintained by Stéphane Lesimple [@speed47][14]. [1]: http://kernsec.org/wiki/index.php/Kernel_Self_Protection_Project/Recommended_Settings [2]: https://docs.clip-os.org/clipos/kernel.html#configuration [3]: https://grsecurity.net/ [4]: https://github.com/a13xp0p0v/linux-kernel-defence-map [5]: https://lwn.net/Articles/791863/ [6]: https://github.com/a13xp0p0v/kconfig-hardened-check/issues/38 [7]: https://github.com/BlackIkeEagle [8]: https://blog.herecura.eu/blog/2020-05-30-kconfig-hardening-tests/ [9]: https://googleprojectzero.blogspot.com/2018/09/a-cache-invalidation-bug-in-linux.html [10]: https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html [11]: https://github.com/tych0/huldufolk [12]: https://github.com/tych0 [13]: https://github.com/speed47/spectre-meltdown-checker [14]: https://github.com/speed47 [15]: https://github.com/a13xp0p0v/kconfig-hardened-check/issues/53 [16]: https://github.com/a13xp0p0v/kconfig-hardened-check/pull/54