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,
- CLIP OS kernel configuration,
- last public grsecurity patch (options which they disable).
I also created Linux Kernel Defence Map that is a graphical representation of the relationships between these hardening features and the corresponding vulnerability classes or exploitation techniques.
- X86_64
- X86_32
- ARM64
- ARM
usage: kconfig-hardened-check.py [-h] [-p {X86_64,X86_32,ARM64,ARM}]
[-c CONFIG] [--debug] [--json]
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 (not for production use)
--json print results in JSON format
$ ./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
[+] Trying to detect kernel version in "config_files/distros/ubuntu-bionic-generic.config"...
[+] Found version line: "# Linux/x86 5.3.0-28-generic Kernel Configuration"
[+] Detected kernel version: 5.3
[+] Checking "config_files/distros/ubuntu-bionic-generic.config" against X86_64 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_SLUB_DEBUG | y |defconfig | self_protection | OK
CONFIG_STRICT_MODULE_RWX | y |defconfig | self_protection | OK
CONFIG_GCC_PLUGINS | y |defconfig | self_protection | FAIL: not found
CONFIG_REFCOUNT_FULL | y |defconfig | self_protection | FAIL: "is not set"
CONFIG_MICROCODE | y |defconfig | self_protection | OK
CONFIG_RETPOLINE | y |defconfig | self_protection | OK
CONFIG_X86_SMAP | y |defconfig | self_protection | OK
CONFIG_X86_UMIP | y |defconfig | self_protection | OK: CONFIG_X86_INTEL_UMIP "y"
CONFIG_IOMMU_SUPPORT | y |defconfig | self_protection | OK
CONFIG_SYN_COOKIES | y |defconfig | self_protection | OK
CONFIG_PAGE_TABLE_ISOLATION | y |defconfig | self_protection | OK
CONFIG_RANDOMIZE_MEMORY | y |defconfig | self_protection | OK
CONFIG_INTEL_IOMMU | y |defconfig | self_protection | OK
CONFIG_AMD_IOMMU | y |defconfig | self_protection | OK
CONFIG_VMAP_STACK | y |defconfig | self_protection | OK
CONFIG_RANDOMIZE_BASE | 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_SHUFFLE_PAGE_ALLOCATOR | y | kspp | self_protection | OK
CONFIG_FORTIFY_SOURCE | y | kspp | self_protection | OK
CONFIG_GCC_PLUGIN_RANDSTRUCT | 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_HARDENED_USERCOPY | y | kspp | self_protection | OK
CONFIG_HARDENED_USERCOPY_FALLBACK | is not set | kspp | self_protection | FAIL: "y"
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_INIT_STACK_ALL | y | kspp | self_protection | FAIL: not found
CONFIG_INIT_ON_ALLOC_DEFAULT_ON | y | kspp | self_protection | OK
CONFIG_INIT_ON_FREE_DEFAULT_ON | y | kspp | self_protection | OK: CONFIG_PAGE_POISONING "y"
CONFIG_GCC_PLUGIN_STACKLEAK | y | kspp | self_protection | FAIL: not found
CONFIG_STACKLEAK_METRICS | is not set | clipos | self_protection | FAIL: CONFIG_GCC_PLUGIN_STACKLEAK is needed
CONFIG_STACKLEAK_RUNTIME_DISABLE | is not set | clipos | self_protection | FAIL: CONFIG_GCC_PLUGIN_STACKLEAK is needed
CONFIG_DEFAULT_MMAP_MIN_ADDR | 65536 | kspp | self_protection | OK
CONFIG_SECURITY_DMESG_RESTRICT | y | clipos | self_protection | FAIL: "is not set"
CONFIG_DEBUG_VIRTUAL | y | clipos | self_protection | FAIL: "is not set"
CONFIG_STATIC_USERMODEHELPER | y | clipos | self_protection | FAIL: "is not set"
CONFIG_SLAB_MERGE_DEFAULT | is not set | clipos | self_protection | FAIL: "y"
CONFIG_GCC_PLUGIN_RANDSTRUCT_PERFORMANCE | is not set | clipos | self_protection | FAIL: CONFIG_GCC_PLUGIN_RANDSTRUCT is needed
CONFIG_RANDOM_TRUST_CPU | is not set | clipos | self_protection | FAIL: "y"
CONFIG_INTEL_IOMMU_SVM | y | clipos | self_protection | OK
CONFIG_INTEL_IOMMU_DEFAULT_ON | y | clipos | self_protection | FAIL: "is not set"
CONFIG_SLUB_DEBUG_ON | y | my | self_protection | FAIL: "is not set"
CONFIG_RESET_ATTACK_MITIGATION | y | my | self_protection | OK
CONFIG_AMD_IOMMU_V2 | y | my | self_protection | FAIL: "m"
CONFIG_SECURITY | y |defconfig | security_policy | OK
CONFIG_SECURITY_YAMA | y | kspp | security_policy | OK
CONFIG_SECURITY_LOADPIN | y | my | security_policy | FAIL: "is not set"
CONFIG_SECURITY_LOCKDOWN_LSM | y | my | security_policy | FAIL: not found
CONFIG_SECURITY_LOCKDOWN_LSM_EARLY | y | my | security_policy | FAIL: not found
CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY| y | my | security_policy | FAIL: not found
CONFIG_SECURITY_SAFESETID | y | my | security_policy | OK
CONFIG_SECURITY_WRITABLE_HOOKS | is not set | my | security_policy | OK: not found
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_KSM | is not set | clipos | cut_attack_surface | FAIL: "y"
CONFIG_KALLSYMS | is not set | clipos | cut_attack_surface | FAIL: "y"
CONFIG_X86_VSYSCALL_EMULATION | is not set | clipos | cut_attack_surface | FAIL: "y"
CONFIG_MAGIC_SYSRQ | is not set | clipos | cut_attack_surface | FAIL: "y"
CONFIG_KEXEC_FILE | is not set | clipos | cut_attack_surface | FAIL: "y"
CONFIG_USER_NS | is not set | clipos | cut_attack_surface | FAIL: "y"
CONFIG_LDISC_AUTOLOAD | is not set | clipos | cut_attack_surface | FAIL: "y"
CONFIG_MMIOTRACE | is not set | my | cut_attack_surface | FAIL: "y"
CONFIG_LIVEPATCH | 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_VIDEO_VIVID | is not set | my | cut_attack_surface | FAIL: "m"
CONFIG_ARCH_MMAP_RND_BITS | 32 | clipos |userspace_hardening | FAIL: "28"
[+] config check is finished: 'OK' - 50 / 'FAIL' - 73
I usually update the kernel 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]
The current version of kconfig-hardened-check is 0.5.3, it's marked with the git tag.
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.
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.
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