# kernel-hardening-checker

__(formerly kconfig-hardened-check)__<br /><br />
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## Motivation

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!

__kernel-hardening-checker__ (formerly __kconfig-hardened-check__) is a tool for checking the security hardening options of the Linux kernel. It supports checking:

  - Kconfig options (compile-time)
  - Kernel cmdline arguments (boot-time)
  - Sysctl parameters (runtime)

The security hardening recommendations are based on:

  - [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 the Linux kernel maintainers][23]

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

__Attention!__ Changing Linux kernel security parameters may also affect system performance
and functionality of userspace software. So for choosing these parameters, consider
the threat model of your Linux-based information system and perform thorough testing
of its typical workload.

## Repositories

 - Main at GitHub <https://github.com/a13xp0p0v/kernel-hardening-checker>
 - Mirror at Codeberg: <https://codeberg.org/a13xp0p0v/kernel-hardening-checker>
 - Mirror at GitFlic: <https://gitflic.ru/project/a13xp0p0v/kernel-hardening-checker>

## Supported microarchitectures

  - X86_64
  - X86_32
  - ARM64
  - ARM

TODO: RISC-V (issue [#56][22])

## Installation

You can install the package:

```
pip install git+https://github.com/a13xp0p0v/kernel-hardening-checker
```

or simply run `./bin/kernel-hardening-checker` from the cloned repository.

Some Linux distributions also provide `kernel-hardening-checker` as a package.

## Usage
```
usage: kernel-hardening-checker [-h] [--version] [-m {verbose,json,show_ok,show_fail}]
                                [-c CONFIG] [-l CMDLINE] [-s SYSCTL] [-v KERNEL_VERSION]
                                [-p {X86_64,X86_32,ARM64,ARM}]
                                [-g {X86_64,X86_32,ARM64,ARM}]

A tool for checking the security hardening options of the Linux kernel

options:
  -h, --help            show this help message and exit
  --version             show program's version number and exit
  -m {verbose,json,show_ok,show_fail}, --mode {verbose,json,show_ok,show_fail}
                        choose the report mode
  -c CONFIG, --config CONFIG
                        check the security hardening options in the kernel Kconfig file
                        (also supports *.gz files)
  -l CMDLINE, --cmdline CMDLINE
                        check the security hardening options in the kernel cmdline file
                        (contents of /proc/cmdline)
  -s SYSCTL, --sysctl SYSCTL
                        check the security hardening options in the sysctl output file
                        (`sudo sysctl -a > file`)
  -v KERNEL_VERSION, --kernel-version KERNEL_VERSION
                        extract the version from the kernel version file (contents of
                        /proc/version)
  -p {X86_64,X86_32,ARM64,ARM}, --print {X86_64,X86_32,ARM64,ARM}
                        print the security hardening recommendations for the selected
                        microarchitecture
  -g {X86_64,X86_32,ARM64,ARM}, --generate {X86_64,X86_32,ARM64,ARM}
                        generate a Kconfig fragment with the security hardening options
                        for the selected microarchitecture
```

## Output modes

  -  no `-m` argument for the default output mode (see the example below)
  - `-m verbose` for printing additional info:
    - config options without a corresponding check
    - internals of complex checks with AND/OR, like this:
```
-------------------------------------------------------------------------------------------
    <<< OR >>>                                                                             
CONFIG_STRICT_DEVMEM                    |kconfig|     y      |defconfig |cut_attack_surface
CONFIG_DEVMEM                           |kconfig| is not set |   kspp   |cut_attack_surface
-------------------------------------------------------------------------------------------
```
  - `-m show_fail` for showing only the failed checks
  - `-m show_ok` for showing only the successful checks
  - `-m json` for printing the results in JSON format (for combining `kernel-hardening-checker` with other tools)

## Example output for `Fedora 38` kernel configuration
```
$ ./bin/kernel-hardening-checker -c kernel_hardening_checker/config_files/distros/fedora_38.config -l /proc/cmdline -s kernel_hardening_checker/config_files/distros/example_sysctls.txt
[+] Kconfig file to check: kernel_hardening_checker/config_files/distros/fedora_38.config
[+] Kernel cmdline file to check: /proc/cmdline
[+] Sysctl output file to check: kernel_hardening_checker/config_files/distros/example_sysctls.txt
[+] Detected microarchitecture: X86_64
[+] Detected kernel version: 6.3
[+] Detected compiler: GCC 130101
=========================================================================================================================
              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_THREAD_INFO_IN_TASK              |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_GCC_PLUGINS                      |kconfig|     y      |defconfig | self_protection  | FAIL: "is not set"
CONFIG_IOMMU_SUPPORT                    |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_STACKPROTECTOR                   |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_STACKPROTECTOR_STRONG            |kconfig|     y      |defconfig | self_protection  | OK
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_RANDOMIZE_BASE                   |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_VMAP_STACK                       |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_DEBUG_WX                         |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_WERROR                           |kconfig|     y      |defconfig | self_protection  | FAIL: "is not set"
CONFIG_X86_MCE                          |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_X86_MCE_INTEL                    |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_X86_MCE_AMD                      |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_MICROCODE                        |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_RETPOLINE                        |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_SYN_COOKIES                      |kconfig|     y      |defconfig | self_protection  | OK
CONFIG_X86_SMAP                         |kconfig|     y      |defconfig | self_protection  | OK: version >= 5.19
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_X86_KERNEL_IBT                   |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_BUG_ON_DATA_CORRUPTION           |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_VIRTUAL                    |kconfig|     y      |   kspp   | self_protection  | FAIL: "is not set"
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_KFENCE                           |kconfig|     y      |   kspp   | self_protection  | OK
CONFIG_ZERO_CALL_USED_REGS              |kconfig|     y      |   kspp   | self_protection  | FAIL: "is not set"
CONFIG_HW_RANDOM_TPM                    |kconfig|     y      |   kspp   | self_protection  | OK
CONFIG_STATIC_USERMODEHELPER            |kconfig|     y      |   kspp   | self_protection  | FAIL: "is not set"
CONFIG_RANDSTRUCT_FULL                  |kconfig|     y      |   kspp   | self_protection  | FAIL: is not found
CONFIG_RANDSTRUCT_PERFORMANCE           |kconfig| is not set |   kspp   | self_protection  | FAIL: CONFIG_RANDSTRUCT_FULL is not "y"
CONFIG_HARDENED_USERCOPY                |kconfig|     y      |   kspp   | self_protection  | OK
CONFIG_HARDENED_USERCOPY_FALLBACK       |kconfig| is not set |   kspp   | self_protection  | OK: is not found
CONFIG_HARDENED_USERCOPY_PAGESPAN       |kconfig| is not set |   kspp   | self_protection  | OK: is not found
CONFIG_GCC_PLUGIN_LATENT_ENTROPY        |kconfig|     y      |   kspp   | self_protection  | FAIL: CONFIG_GCC_PLUGINS is not "y"
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  | OK
CONFIG_INIT_ON_FREE_DEFAULT_ON          |kconfig|     y      |   kspp   | self_protection  | FAIL: "is not set"
CONFIG_EFI_DISABLE_PCI_DMA              |kconfig|     y      |   kspp   | self_protection  | FAIL: "is not set"
CONFIG_RESET_ATTACK_MITIGATION          |kconfig|     y      |   kspp   | self_protection  | FAIL: "is not set"
CONFIG_UBSAN_BOUNDS                     |kconfig|     y      |   kspp   | self_protection  | FAIL: is not found
CONFIG_UBSAN_LOCAL_BOUNDS               |kconfig|     y      |   kspp   | self_protection  | FAIL: is not found
CONFIG_UBSAN_TRAP                       |kconfig|     y      |   kspp   | self_protection  | FAIL: CONFIG_UBSAN_BOUNDS is not "y"
CONFIG_UBSAN_SANITIZE_ALL               |kconfig|     y      |   kspp   | self_protection  | FAIL: CONFIG_UBSAN_BOUNDS is not "y"
CONFIG_GCC_PLUGIN_STACKLEAK             |kconfig|     y      |   kspp   | self_protection  | FAIL: CONFIG_GCC_PLUGINS is not "y"
CONFIG_STACKLEAK_METRICS                |kconfig| is not set |   kspp   | self_protection  | FAIL: CONFIG_GCC_PLUGINS is not "y"
CONFIG_STACKLEAK_RUNTIME_DISABLE        |kconfig| is not set |   kspp   | self_protection  | FAIL: CONFIG_GCC_PLUGINS is not "y"
CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT  |kconfig|     y      |   kspp   | self_protection  | OK
CONFIG_CFI_CLANG                        |kconfig|     y      |   kspp   | self_protection  | FAIL: is not found
CONFIG_CFI_PERMISSIVE                   |kconfig| is not set |   kspp   | self_protection  | FAIL: CONFIG_CFI_CLANG is not "y"
CONFIG_SCHED_CORE                       |kconfig|     y      |   kspp   | self_protection  | OK
CONFIG_DEFAULT_MMAP_MIN_ADDR            |kconfig|   65536    |   kspp   | self_protection  | OK
CONFIG_IOMMU_DEFAULT_DMA_STRICT         |kconfig|     y      |   kspp   | self_protection  | FAIL: "is not set"
CONFIG_IOMMU_DEFAULT_PASSTHROUGH        |kconfig| is not set |   kspp   | self_protection  | OK
CONFIG_INTEL_IOMMU_DEFAULT_ON           |kconfig|     y      |   kspp   | self_protection  | FAIL: "is not set"
CONFIG_SLS                              |kconfig|     y      |   kspp   | self_protection  | OK
CONFIG_INTEL_IOMMU_SVM                  |kconfig|     y      |   kspp   | self_protection  | OK
CONFIG_AMD_IOMMU_V2                     |kconfig|     y      |   kspp   | self_protection  | FAIL: "m"
CONFIG_SLAB_MERGE_DEFAULT               |kconfig| is not set |  clipos  | self_protection  | OK
CONFIG_SECURITY                         |kconfig|     y      |defconfig | security_policy  | OK
CONFIG_SECURITY_YAMA                    |kconfig|     y      |   kspp   | security_policy  | OK
CONFIG_SECURITY_LANDLOCK                |kconfig|     y      |   kspp   | security_policy  | OK
CONFIG_SECURITY_SELINUX_DISABLE         |kconfig| is not set |   kspp   | security_policy  | OK
CONFIG_SECURITY_SELINUX_BOOTPARAM       |kconfig| is not set |   kspp   | security_policy  | FAIL: "y"
CONFIG_SECURITY_SELINUX_DEVELOP         |kconfig| is not set |   kspp   | security_policy  | FAIL: "y"
CONFIG_SECURITY_LOCKDOWN_LSM            |kconfig|     y      |   kspp   | security_policy  | OK
CONFIG_SECURITY_LOCKDOWN_LSM_EARLY      |kconfig|     y      |   kspp   | security_policy  | OK
CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY|kconfig|     y      |   kspp   | security_policy  | FAIL: "is not set"
CONFIG_SECURITY_WRITABLE_HOOKS          |kconfig| is not set |   kspp   | security_policy  | OK: is not found
CONFIG_SECURITY_SELINUX                 |kconfig|     y      |    my    | security_policy  | OK
CONFIG_SECCOMP                          |kconfig|     y      |defconfig |cut_attack_surface| OK
CONFIG_SECCOMP_FILTER                   |kconfig|     y      |defconfig |cut_attack_surface| OK
CONFIG_BPF_UNPRIV_DEFAULT_OFF           |kconfig|     y      |defconfig |cut_attack_surface| OK
CONFIG_STRICT_DEVMEM                    |kconfig|     y      |defconfig |cut_attack_surface| OK
CONFIG_X86_INTEL_TSX_MODE_OFF           |kconfig|     y      |defconfig |cut_attack_surface| OK
CONFIG_SECURITY_DMESG_RESTRICT          |kconfig|     y      |   kspp   |cut_attack_surface| FAIL: "is not set"
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: is not found
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_COMPAT                           |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: is not found
CONFIG_X86_X32_ABI                      |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: is 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_LDISC_AUTOLOAD                   |kconfig| is not set |   kspp   |cut_attack_surface| FAIL: "y"
CONFIG_COMPAT_VDSO                      |kconfig| is not set |   kspp   |cut_attack_surface| OK
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: is 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: is 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: is 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: is 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
CONFIG_NOUVEAU_LEGACY_CTX_SUPPORT       |kconfig| is not set |maintainer|cut_attack_surface| OK: is not found
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_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_COREDUMP                         |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_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_BPF_SYSCALL                      |kconfig| is not set | lockdown |cut_attack_surface| FAIL: "y"
CONFIG_LEGACY_TIOCSTI                   |kconfig| is not set |    my    |cut_attack_surface| OK
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| FAIL: "m"
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_AIO                              |kconfig| is not set |    my    |cut_attack_surface| FAIL: "y"
CONFIG_CORESIGHT                        |kconfig| is not set |    my    |cut_attack_surface| OK: is not found
CONFIG_XFS_SUPPORT_V4                   |kconfig| is not set |    my    |cut_attack_surface| FAIL: "y"
CONFIG_TRIM_UNUSED_KSYMS                |kconfig|     y      |    my    |cut_attack_surface| FAIL: is not found
CONFIG_ARCH_MMAP_RND_BITS               |kconfig|     32     |    my    | harden_userspace | FAIL: "28"
nosmep                                  |cmdline| is not set |defconfig | self_protection  | OK: is not found
nosmap                                  |cmdline| is not set |defconfig | self_protection  | OK: is not found
nokaslr                                 |cmdline| is not set |defconfig | self_protection  | OK: is not found
nopti                                   |cmdline| is not set |defconfig | self_protection  | OK: is not found
nospectre_v1                            |cmdline| is not set |defconfig | self_protection  | OK: is not found
nospectre_v2                            |cmdline| is not set |defconfig | self_protection  | OK: is not found
nospectre_bhb                           |cmdline| is not set |defconfig | self_protection  | OK: is not found
nospec_store_bypass_disable             |cmdline| is not set |defconfig | self_protection  | OK: is not found
arm64.nobti                             |cmdline| is not set |defconfig | self_protection  | OK: is not found
arm64.nopauth                           |cmdline| is not set |defconfig | self_protection  | OK: is not found
arm64.nomte                             |cmdline| is not set |defconfig | self_protection  | OK: is not found
spectre_v2                              |cmdline| is not off |defconfig | self_protection  | FAIL: is off, not found
spectre_v2_user                         |cmdline| is not off |defconfig | self_protection  | FAIL: is off, not found
spec_store_bypass_disable               |cmdline| is not off |defconfig | self_protection  | FAIL: is off, not found
l1tf                                    |cmdline| is not off |defconfig | self_protection  | FAIL: is off, not found
mds                                     |cmdline| is not off |defconfig | self_protection  | FAIL: is off, not found
tsx_async_abort                         |cmdline| is not off |defconfig | self_protection  | FAIL: is off, not found
srbds                                   |cmdline| is not off |defconfig | self_protection  | FAIL: is off, not found
mmio_stale_data                         |cmdline| is not off |defconfig | self_protection  | FAIL: is off, not found
retbleed                                |cmdline| is not off |defconfig | self_protection  | FAIL: is off, not found
rodata                                  |cmdline|     on     |defconfig | self_protection  | OK: rodata is not found
nosmt                                   |cmdline| is present |   kspp   | self_protection  | FAIL: is not present
mitigations                             |cmdline| auto,nosmt |   kspp   | self_protection  | FAIL: is not found
slab_merge                              |cmdline| is not set |   kspp   | self_protection  | OK: is not found
slub_merge                              |cmdline| is not set |   kspp   | self_protection  | OK: is not found
slab_nomerge                            |cmdline| is present |   kspp   | self_protection  | OK: CONFIG_SLAB_MERGE_DEFAULT is "is not set"
init_on_alloc                           |cmdline|     1      |   kspp   | self_protection  | FAIL: is not found
init_on_free                            |cmdline|     1      |   kspp   | self_protection  | FAIL: is not found
hardened_usercopy                       |cmdline|     1      |   kspp   | self_protection  | OK: CONFIG_HARDENED_USERCOPY is "y"
slab_common.usercopy_fallback           |cmdline|     0      |   kspp   | self_protection  | OK: CONFIG_HARDENED_USERCOPY_FALLBACK is not found
iommu.strict                            |cmdline|     1      |   kspp   | self_protection  | FAIL: is not found
iommu.passthrough                       |cmdline|     0      |   kspp   | self_protection  | OK: CONFIG_IOMMU_DEFAULT_PASSTHROUGH is "is not set"
randomize_kstack_offset                 |cmdline|     1      |   kspp   | self_protection  | OK: CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT is "y"
pti                                     |cmdline|     on     |   kspp   | self_protection  | FAIL: is not found
page_alloc.shuffle                      |cmdline|     1      |  clipos  | self_protection  | FAIL: is not found
iommu                                   |cmdline|   force    |  clipos  | self_protection  | FAIL: is not found
tsx                                     |cmdline|    off     |defconfig |cut_attack_surface| OK: CONFIG_X86_INTEL_TSX_MODE_OFF is "y"
vsyscall                                |cmdline|    none    |   kspp   |cut_attack_surface| FAIL: is not found
vdso32                                  |cmdline|     1      |    my    |cut_attack_surface| OK: CONFIG_COMPAT_VDSO is "is not set"
debugfs                                 |cmdline|    off     |  grsec   |cut_attack_surface| FAIL: is not found
sysrq_always_enabled                    |cmdline| is not set |    my    |cut_attack_surface| OK: is not found
norandmaps                              |cmdline| is not set |defconfig | harden_userspace | OK: is not found
net.core.bpf_jit_harden                 |sysctl |     2      |   kspp   | self_protection  | FAIL: "0"
kernel.dmesg_restrict                   |sysctl |     1      |   kspp   |cut_attack_surface| FAIL: "0"
kernel.perf_event_paranoid              |sysctl |     3      |   kspp   |cut_attack_surface| FAIL: "2"
kernel.kexec_load_disabled              |sysctl |     1      |   kspp   |cut_attack_surface| FAIL: "0"
user.max_user_namespaces                |sysctl |     0      |   kspp   |cut_attack_surface| FAIL: "31021"
dev.tty.ldisc_autoload                  |sysctl |     0      |   kspp   |cut_attack_surface| FAIL: "1"
kernel.unprivileged_bpf_disabled        |sysctl |     1      |   kspp   |cut_attack_surface| OK

[+] Config check is finished: 'OK' - 118 / 'FAIL' - 119
```

## Generating a Kconfig fragment with the security hardening options

With the `-g` argument, the tool generates a Kconfig fragment with the security hardening options for the selected microarchitecture.

This Kconfig fragment can be merged with the existing Linux kernel config:
```
$ ./bin/kernel-hardening-checker -g X86_64 > /tmp/fragment
$ cd ~/linux-src/
$ ./scripts/kconfig/merge_config.sh .config /tmp/fragment
Using .config as base
Merging /tmp/fragment
Value of CONFIG_BUG_ON_DATA_CORRUPTION is redefined by fragment /tmp/fragment:
Previous value: # CONFIG_BUG_ON_DATA_CORRUPTION is not set
New value: CONFIG_BUG_ON_DATA_CORRUPTION=y
 ...
```

## Questions and answers

__Q:__ How all these kernel parameters influence the Linux kernel security?

__A:__ To answer this question, you can use the `kernel-hardening-checker` [sources of recommendations][24]
and the [Linux Kernel Defence Map][4] with its references.

<br />

__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:

  - An 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:__ 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 decreases system safety (kernel oops is still not a rare situation)
  - It allows easier denial-of-service attacks for the whole system

I think having `CONFIG_BUG` is enough here.
If a kernel oops happens in the process context, the offending/attacking process is killed.
In other cases, the kernel panics, which is similar to `CONFIG_PANIC_ON_OOPS=y`.

<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:__ What about performance impact of these security hardening options?

__A:__ Ike Devolder [@BlackIkeEagle][7] made some performance tests and described the results in [this article][8].
A more detailed evaluation is in the TODO list (the issue [#66][21]).

<br />

__Q:__ Can I easily check which kernel versions support some Kconfig option?

__A:__ Yes. See the [LKDDb][18] project (Linux Kernel Driver Database) by Giacomo Catenazzi [@cateee][19].
You can use it for the `mainline` or `stable` tree from [kernel.org][20] or for your custom kernel sources.

<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].

<br />

__Q:__ Why the `CONFIG_GCC_PLUGINS` option 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/
[4]: https://github.com/a13xp0p0v/linux-kernel-defence-map
[5]: https://lwn.net/Articles/791863/
[6]: https://github.com/a13xp0p0v/kernel-hardening-checker/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
[15]: https://github.com/a13xp0p0v/kernel-hardening-checker/issues/53
[16]: https://github.com/a13xp0p0v/kernel-hardening-checker/pull/54
[17]: https://github.com/a13xp0p0v/kernel-hardening-checker/pull/62
[18]: https://cateee.net/lkddb/web-lkddb/
[19]: https://github.com/cateee/lkddb
[20]: https://kernel.org/
[21]: https://github.com/a13xp0p0v/kernel-hardening-checker/issues/66
[22]: https://github.com/a13xp0p0v/kernel-hardening-checker/issues/56
[23]: https://github.com/a13xp0p0v/kernel-hardening-checker/issues?q=label%3Akernel_maintainer_feedback
[24]: https://github.com/a13xp0p0v/kernel-hardening-checker#motivation
