There are plenty of security hardening options for 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 options against my security hardening preferences, which are based on the
- KSPP recommended settings,
- CLIP OS kernel configuration,
- Last public grsecurity patch (options which they disable),
- SECURITY_LOCKDOWN_LSM patchset,
- Direct feedback from Linux kernel maintainers (see #38, #53, #54, #62).
This tool supports checking Kconfig options and kernel cmdline parameters.
I also created Linux Kernel Defence Map that is a graphical representation of the relationships between security hardening features and the corresponding vulnerability classes or exploitation techniques.
- X86_64
- X86_32
- ARM64
- ARM
TODO: RISC-V
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: kconfig-hardened-check [-h] [--version] [-p {X86_64,X86_32,ARM64,ARM}]
[-c CONFIG]
[-l CMDLINE]
[-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 kconfig file against these preferences
-l CMDLINE, --cmdline CMDLINE
check the kernel cmdline file against these preferences
-m {verbose,json,show_ok,show_fail}, --mode {verbose,json,show_ok,show_fail}
choose the report mode
- no
-margument for the default output mode (see the example below) -m verbosefor 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_failfor showing only the failed checks-m show_okfor showing only the successful checks-m jsonfor printing the results in JSON format (for combiningkconfig-hardened-checkwith other tools)
$ ./bin/kconfig-hardened-check -c /boot/config-5.16.20-100.fc34.x86_64 -l /proc/cmdline
[+] Kconfig file to check: /boot/config-5.16.20-100.fc34.x86_64
[+] Kernel cmdline file to check: /proc/cmdline
[+] Detected architecture: X86_64
[+] Detected kernel version: 5.16
=========================================================================================================================
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 | OK
CONFIG_STACKPROTECTOR |kconfig| y |defconfig | self_protection | OK
CONFIG_STACKPROTECTOR_STRONG |kconfig| y |defconfig | self_protection | FAIL: "is not set"
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 | OK: version >= 5.5
CONFIG_THREAD_INFO_IN_TASK |kconfig| y |defconfig | self_protection | OK
CONFIG_IOMMU_SUPPORT |kconfig| y |defconfig | self_protection | OK
CONFIG_RANDOMIZE_BASE |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_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 | OK
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 | OK
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 | FAIL: "is not set"
CONFIG_GCC_PLUGIN_LATENT_ENTROPY |kconfig| y | kspp | self_protection | FAIL: "is not set"
CONFIG_KFENCE |kconfig| y | kspp | self_protection | OK
CONFIG_WERROR |kconfig| y | kspp | self_protection | FAIL: "is not set"
CONFIG_IOMMU_DEFAULT_DMA_STRICT |kconfig| y | kspp | self_protection | FAIL: "is not set"
CONFIG_ZERO_CALL_USED_REGS |kconfig| y | kspp | self_protection | FAIL: "is not set"
CONFIG_GCC_PLUGIN_RANDSTRUCT |kconfig| y | kspp | self_protection | FAIL: "is not set"
CONFIG_HARDENED_USERCOPY |kconfig| y | kspp | self_protection | OK
CONFIG_HARDENED_USERCOPY_FALLBACK |kconfig| is not set | kspp | self_protection | OK: not found
CONFIG_HARDENED_USERCOPY_PAGESPAN |kconfig| is not set | kspp | self_protection | OK: not found
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 | FAIL: "is not set"
CONFIG_GCC_PLUGIN_STACKLEAK |kconfig| y | kspp | self_protection | FAIL: "is not set"
CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT |kconfig| y | kspp | self_protection | FAIL: "is not set"
CONFIG_SCHED_CORE |kconfig| y | kspp | self_protection | OK
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: "is not set"
CONFIG_SLAB_MERGE_DEFAULT |kconfig| is not set | clipos | self_protection | OK
CONFIG_RANDOM_TRUST_BOOTLOADER |kconfig| is not set | clipos | self_protection | OK
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 | FAIL: "is not set"
CONFIG_SLS |kconfig| y | my | self_protection | FAIL: not found
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_SELINUX_DISABLE |kconfig| is not set | kspp | security_policy | OK
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_WRITABLE_HOOKS |kconfig| is not set | my | security_policy | OK: not found
CONFIG_SECURITY_SAFESETID |kconfig| y | my | security_policy | FAIL: "is not set"
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_BPF_UNPRIV_DEFAULT_OFF |kconfig| y |defconfig |cut_attack_surface| OK
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: not found
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: "y"
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| OK
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| OK
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_X86_MSR |kconfig| is not set | kspp |cut_attack_surface| FAIL: "y"
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| OK
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| FAIL: "y"
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| OK
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| OK
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| OK
CONFIG_ACPI_CONFIGFS |kconfig| is not set | grsec |cut_attack_surface| OK
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: not found
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| OK
CONFIG_MTD_PHRAM |kconfig| is not set | grsec |cut_attack_surface| OK
CONFIG_IO_URING |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y"
CONFIG_KCMP |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y"
CONFIG_RSEQ |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y"
CONFIG_LATENCYTOP |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y"
CONFIG_KCOV |kconfig| is not set | grsec |cut_attack_surface| OK
CONFIG_PROVIDE_OHCI1394_DMA_INIT |kconfig| is not set | grsec |cut_attack_surface| FAIL: "y"
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
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_BLK_DEV_FD_RAWCMD |kconfig| is not set |maintainer|cut_attack_surface| OK: not found
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_CPUID |kconfig| is not set | clipos |cut_attack_surface| FAIL: "y"
CONFIG_X86_IOPL_IOPERM |kconfig| is not set | clipos |cut_attack_surface| FAIL: "y"
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| FAIL: "y"
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_BPF_SYSCALL |kconfig| is not set | lockdown |cut_attack_surface| FAIL: "y"
CONFIG_EFI_TEST |kconfig| is not set | lockdown |cut_attack_surface| FAIL: "m"
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| OK
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| OK: not found
CONFIG_INPUT_EVBUG |kconfig| is not set | my |cut_attack_surface| OK
CONFIG_KGDB |kconfig| is not set | my |cut_attack_surface| FAIL: "y"
CONFIG_INTEGRITY |kconfig| y |defconfig | harden_userspace | OK
CONFIG_ARCH_MMAP_RND_BITS |kconfig| 32 | clipos | harden_userspace | FAIL: "28"
pti |cmdline| on | kspp | self_protection | FAIL: not found
[+] Config check is finished: 'OK' - 82 / 'FAIL' - 94
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]
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_NSand 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: NixOS/nixpkgs#84522 (comment)
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 made some performance tests and described the results in this article.
Q: Can I easily check which kernel versions support some Kconfig option?
A: Yes, see the LKDDb project (Linux Kernel Driver Database) by Giacomo Catenazzi @cateee.
You can use it for the mainline or stable tree from kernel.org or for your custom kernel sources.
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, example 2). CONFIG_STATIC_USERMODEHELPER prevents that method. But it
requires the corresponding support in the userspace: see the example implementation by
Tycho Andersen @tych0.
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 tool maintained by Stéphane Lesimple @speed47.