# 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 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),
  - [SECURITY_LOCKDOWN_LSM][5] patchset,
  - direct feedback from Linux kernel maintainers (Daniel Vetter in [issue #38][6]).

I also created [__Linux Kernel Defence Map__][4] that is a graphical representation of the
relationships between these hardening features and the corresponding vulnerability classes
or exploitation techniques.

## Supported microarchitectures

  - X86_64
  - X86_32
  - ARM64
  - ARM

## 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.

## Usage
```
usage: kconfig-hardened-check [-h] [--version] [-p {X86_64,X86_32,ARM64,ARM}]
                              [-c CONFIG]
                              [-m {verbose,json,show_ok,show_fail}]

Checks the hardening options in the Linux kernel config

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 hardening preferences for 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 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                 | desired val | decision |       reason       |   check result
=========================================================================================================================
CONFIG_BUG                                   |      y      |defconfig |  self_protection   |   OK
CONFIG_SLUB_DEBUG                            |      y      |defconfig |  self_protection   |   OK
CONFIG_GCC_PLUGINS                           |      y      |defconfig |  self_protection   |   FAIL: not found
CONFIG_STACKPROTECTOR_STRONG                 |      y      |defconfig |  self_protection   |   OK
CONFIG_STRICT_KERNEL_RWX                     |      y      |defconfig |  self_protection   |   OK
CONFIG_STRICT_MODULE_RWX                     |      y      |defconfig |  self_protection   |   OK
CONFIG_REFCOUNT_FULL                         |      y      |defconfig |  self_protection   |   FAIL: "is not set"
CONFIG_IOMMU_SUPPORT                         |      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_SYN_COOKIES                           |      y      |defconfig |  self_protection   |   OK
CONFIG_X86_UMIP                              |      y      |defconfig |  self_protection   |   OK: CONFIG_X86_INTEL_UMIP "y"
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_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_INIT_ON_ALLOC_DEFAULT_ON              |      y      |   kspp   |  self_protection   |   OK
CONFIG_GCC_PLUGIN_LATENT_ENTROPY             |      y      |   kspp   |  self_protection   |   FAIL: not found
CONFIG_GCC_PLUGIN_RANDSTRUCT                 |      y      |   kspp   |  self_protection   |   FAIL: not found
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_ZERO                   |      y      |   kspp   |  self_protection   |   FAIL: not found
CONFIG_INIT_ON_FREE_DEFAULT_ON               |      y      |   kspp   |  self_protection   |   OK: CONFIG_PAGE_POISONING_ZERO "y"
CONFIG_GCC_PLUGIN_STACKLEAK                  |      y      |   kspp   |  self_protection   |   FAIL: not found
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_EFI_DISABLE_PCI_DMA                   |      y      |  clipos  |  self_protection   |   FAIL: not found
CONFIG_SLAB_MERGE_DEFAULT                    | is not set  |  clipos  |  self_protection   |   FAIL: "y"
CONFIG_RANDOM_TRUST_BOOTLOADER               | is not set  |  clipos  |  self_protection   |   FAIL: "y"
CONFIG_RANDOM_TRUST_CPU                      | is not set  |  clipos  |  self_protection   |   FAIL: "y"
CONFIG_GCC_PLUGIN_RANDSTRUCT_PERFORMANCE     | is not set  |  clipos  |  self_protection   |   FAIL: CONFIG_GCC_PLUGIN_RANDSTRUCT not "y"
CONFIG_STACKLEAK_METRICS                     | is not set  |  clipos  |  self_protection   |   FAIL: CONFIG_GCC_PLUGIN_STACKLEAK not "y"
CONFIG_STACKLEAK_RUNTIME_DISABLE             | is not set  |  clipos  |  self_protection   |   FAIL: CONFIG_GCC_PLUGIN_STACKLEAK not "y"
CONFIG_INTEL_IOMMU_SVM                       |      y      |  clipos  |  self_protection   |   OK
CONFIG_INTEL_IOMMU_DEFAULT_ON                |      y      |  clipos  |  self_protection   |   FAIL: "is not set"
CONFIG_UBSAN_BOUNDS                          |      y      |    my    |  self_protection   |   FAIL: CONFIG_UBSAN_TRAP not "y"
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_WRITABLE_HOOKS               | is not set  |    my    |  security_policy   |   OK: not found
CONFIG_SECURITY_LOCKDOWN_LSM                 |      y      |  clipos  |  security_policy   |   OK
CONFIG_SECURITY_LOCKDOWN_LSM_EARLY           |      y      |  clipos  |  security_policy   |   OK
CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY|      y      |  clipos  |  security_policy   |   FAIL: "is not set"
CONFIG_SECURITY_SAFESETID                    |      y      |    my    |  security_policy   |   OK
CONFIG_SECURITY_LOADPIN                      |      y      |    my    |  security_policy   |   FAIL: "is not set"
CONFIG_SECURITY_LOADPIN_ENFORCE              |      y      |    my    |  security_policy   |   FAIL: CONFIG_SECURITY_LOADPIN not "y"
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_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_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_OABI_COMPAT                           | is not set  |   kspp   | cut_attack_surface |   OK: not found
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_LEGACY_VSYSCALL_NONE                  |      y      |   kspp   | cut_attack_surface |   FAIL: "is not set"
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_X86_PTDUMP                            | is not set  |grsecurity| cut_attack_surface |   OK
CONFIG_DRM_LEGACY                            | is not set  |maintainer| cut_attack_surface |   OK
CONFIG_FB                                    | is not set  |maintainer| cut_attack_surface |   FAIL: "y"
CONFIG_VT                                    | is not set  |maintainer| cut_attack_surface |   FAIL: "y"
CONFIG_AIO                                   | is not set  |grapheneos| cut_attack_surface |   FAIL: "y"
CONFIG_STAGING                               | is not set  |  clipos  | cut_attack_surface |   FAIL: "y"
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_X86_MSR                               | is not set  |  clipos  | cut_attack_surface |   FAIL: "m"
CONFIG_X86_CPUID                             | is not set  |  clipos  | cut_attack_surface |   FAIL: "m"
CONFIG_IO_URING                              | is not set  |  clipos  | cut_attack_surface |   FAIL: "y"
CONFIG_X86_IOPL_IOPERM                       | is not set  |  clipos  | cut_attack_surface |   OK: not found
CONFIG_ACPI_TABLE_UPGRADE                    | is not set  |  clipos  | cut_attack_surface |   FAIL: "y"
CONFIG_EFI_CUSTOM_SSDT_OVERLAYS              | is not set  |  clipos  | cut_attack_surface |   OK: not found
CONFIG_LDISC_AUTOLOAD                        | is not set  |  clipos  | cut_attack_surface |   FAIL: "y"
CONFIG_X86_INTEL_TSX_MODE_OFF                |      y      |  clipos  | cut_attack_surface |   OK
CONFIG_EFI_TEST                              | is not set  | lockdown | cut_attack_surface |   FAIL: "m"
CONFIG_BPF_SYSCALL                           | is not set  | lockdown | cut_attack_surface |   FAIL: "y"
CONFIG_MMIOTRACE_TEST                        | is not set  | lockdown | cut_attack_surface |   OK
CONFIG_TRIM_UNUSED_KSYMS                     |      y      |    my    | cut_attack_surface |   FAIL: 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_VIDEO_VIVID                           | is not set  |    my    | cut_attack_surface |   FAIL: "m"
CONFIG_INPUT_EVBUG                           | is not set  |    my    | cut_attack_surface |   FAIL: "m"
CONFIG_INTEGRITY                             |      y      |defconfig |userspace_hardening |   OK
CONFIG_ARCH_MMAP_RND_BITS                    |     32      |  clipos  |userspace_hardening |   FAIL: "28"

[+] Config check is finished: 'OK' - 58 / 'FAIL' - 82
```

## kconfig-hardened-check versioning

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].[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

<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.

<br />

__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.

<br />

__Q:__ What about performance impact of these kernel hardening options?

__A:__ Ike Devolder [@BlackIkeEagle][7] made some performance tests and described the results in [this article][8].

<br />

__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].

<br />

__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
