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
--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
[+] 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_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 | FAIL: not found
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_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_INIT_STACK_ALL | y | clipos | self_protection | FAIL: not found
CONFIG_INIT_ON_ALLOC_DEFAULT_ON | y | clipos | self_protection | FAIL: not found
CONFIG_INIT_ON_FREE_DEFAULT_ON | y | clipos | self_protection | FAIL: not found
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_GCC_PLUGIN_STACKLEAK | y | clipos | 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_RANDOM_TRUST_CPU | is not set | clipos | self_protection | OK: not found
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_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_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_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 | OK: not found
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_ARCH_MMAP_RND_BITS | 32 | clipos |userspace_hardening | FAIL: "28"
[+] config check is finished: 'OK' - 48 / 'FAIL' - 75
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.