# 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][1],
- [CLIP OS kernel configuration][2],
- last public [grsecurity][3] 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_LOCK_DOWN_KERNEL | y | clipos | 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_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_MICROCODE | y | clipos | self_protection || OK
CONFIG_X86_MSR | y | clipos | self_protection || FAIL: "m"
CONFIG_IOMMU_SUPPORT | y | clipos | self_protection || OK
CONFIG_INTEL_IOMMU | y | clipos | self_protection || OK
CONFIG_INTEL_IOMMU_SVM | y | clipos | self_protection || OK
CONFIG_INTEL_IOMMU_DEFAULT_ON | y | clipos | self_protection || FAIL: "is not set"
CONFIG_AMD_IOMMU | y | my | self_protection || OK
CONFIG_AMD_IOMMU_V2 | y | my | self_protection || FAIL: "m"
CONFIG_SLUB_DEBUG_ON | 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_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_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_IKCONFIG | is not set | clipos | cut_attack_surface || OK
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_protection|| FAIL: "28"
[+] config check is finished: 'OK' - 50 / 'FAIL' - 71
```
### 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_NS` and security: https://twitter.com/robertswiecki/status/1095447678949953541
<br />
__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.
[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/