documentation/docs/alpine-desktop-setup/post-install/security.md

# Security

There are a few things that have to be done to optimize the security of the system.

## Apparmor and LSM

Apparmor is a mandatory access control (MAC) mechanism which restricts a programs capabilities. Installation is easy:

```
# apk add apparmor apparmor-profiles
# rc-update add apparmor default
```

Add apparmor and other "Linux Security Modules" to the `cmdline` in `/etc/kernel-hooks/secureboothook.conf`:

```
cmdline="... apparmor=1 lsm=landlock,lockdown,yama,integrity,apparmor"
```

Then reconfigure `kernel-hooks` and reboot for it to take effect:

```
# apk fix kernel-hooks
# reboot
```

You can check the status of apparmor using `apparmor-utils`:

```
# apk add apparmor-utils
# aa-status
```

## Cmdline

There are a lot of kernel settings which can be passed to the command line to make a system more secure. [Madaidans-insecurities page](https://madaidans-insecurities.github.io/guides/linux-hardening.html#kernel) describes each of their function and how they improve security of the system so lets add them to `/etc/kernel-hooks/secureboot.conf`:

```
cmdline="... slab_nomerge init_on_alloc=1 init_on_free=1 page_alloc.shuffle=1 pti=on randomize_kstack_offset=on vsyscall=none debugfs=off module.sig_enforce=1 lockdown=confidentiality mce=0 loglevel=0 iommu=force spectre_v2=on spec_store_bypass_disable=on tsx=off tsx_async_abort=full mds=full l1ft=flush ipv6.disable=1 rd.shell=0 rd.emergency=reboot"
```

After reconfiguring `kernel-hooks` try to reboot and it should boot. Although there are more options that might make the system more secure, these come with a big performance hit most of the time so these settings should do for now. 

> Whilst booting up your system you may see sysctl complaining about ipv6 setting. [It's getting worked on](https://git.bijl.us/lnco/documentation/issues/30).

## Sysctl

More kernel settings can be configured through sysctl. All these settings are also explained on [Madaidans-insecurities page](https://madaidans-insecurities.github.io/guides/linux-hardening.html#kernel). Edit the file `/etc/sysctl.d/main.conf`:

```
# Main security configuration.

## Kernel
kernel.kptr_restrict=2
kernel.dmesg_restrict=1
kernel.printk=3 3 3 3
kernel.unprivileged_bpf_disabled=1
net.core.bpf_jit_harden=2
dev.tty.ldisc_autoload=0
kernel.kexec_load_disabled=1
kernel.sysrq=0
kernel.perf_event_paranoid=3

## Network
net.ipv4.tcp_syncookies=1
net.ipv4.tcp_rfc1337=1
net.ipv4.conf.all.rp_filter=1
net.ipv4.conf.default.rp_filter=1
net.ipv4.conf.all.accept_redirects=0
net.ipv4.conf.default.accept_redirects=0
net.ipv4.conf.all.secure_redirects=0
net.ipv4.conf.default.secure_redirects=0
net.ipv4.conf.all.send_redirects=0
net.ipv4.conf.default.send_redirects=0
net.ipv4.icmp_echo_ignore_all=1
net.ipv4.conf.all.accept_source_route=0
net.ipv4.conf.default.accept_source_route=0
net.ipv4.tcp_sack=0
net.ipv4.tcp_dsack=0
net.ipv4.tcp_fack=0

## User space
kernel.yama.ptrace_scope=2
vm.mmap_rnd_bits=32
vm.mmap_rnd_compat_bits=16
fs.protected_symlinks=1
fs.protected_hardlinks=1
fs.protected_fifos=2
fs.protected_regular=2

## For hardened_malloc
vm.max_map_count=1048576

```

This list is still incomplete.

## Blacklisting modules

WIP

## Linux-Hardened

WIP

## Hardened Malloc (WIP)

Musl's default memory allocator which comes with Alpine Linux is already pretty secure but not as secure as [hardened-malloc](https://github.com/GrapheneOS/hardened_malloc/):

```
# apk add hardened-malloc
```

Then to set it system wide edit `/etc/ld-musl-x86_64.path`:

```
/usr/lib/libhardened_malloc.so
/lib
/usr/lib
/usr/local/lib
```

You can also use the light variant of hardened-malloc because the default one may not work well with some graphical applications:

```
/usr/lib/libhardened_malloc-light.so
```