Magisk/docs/deploy.md

Deployment

(Note: This is not a user tutorial for installing Magisk, this is an explaination of how Magisk can be installed, and a guide for developers to properly deploy Magisk in various different situations)

Systemless

When a user flashes a Magisk zip in custom recoveries or have boot images patched in Magisk Manager, Magisk is installed in this way. This is the only officially supported method to install Magisk on a device. The systemless method installs Magisk into a boot image's ramdisk CPIO, sometimes require additional patches to the kernel.

With the introduction of magiskinit, the systemless installation process has become extremely simple as nearly all setup and patches are done at runtime after the device is booted up. Replacing init in rootfs with our own implementation is required for rooting system-as-root devices systemless-ly - that is why magiskinit was created in the first place.

Here are some background knowledge about system-as-root devices:

• No recovery partition. Recovery and system shares the same kernel in boot, and the ramdisk in the boot image is actually the recovery's ramdisk.
• The root folder (/) and /system are both stored in the system partition.
• When the device boots up, a bootloader will set flags in cmdline so the kernel can decide where to mount rootfs: if booting in recovery mode, mount rootfs from ramdisk; if not, mount rootfs from system with dm-verity enabled.

To install anything systemless-ly, our only choice is to install Magisk files into the ramdisk in boot image. The soultion used in Magisk is to patch the kernel to always boot as recovery mode regardlessly, and we do the rootfs construction and booting ourselves. For more details about how magiskinit works, check the Pre-Init section of Magisk Booting Process.

Here are the bare minimum commands to install Magisk into a stock boot image. Be aware that the actual Magisk installation is far more complicated, the following commands will work but should be treat as proof-of-concepts.

# Push 2 binaries, magiskboot and magiskinit to the device

# Assume the 2 binaries are in the current directory and
# both have executing permissions.

# The path to stock boot image, can be a file or an on-device block
BOOTIMAGE=<path to boot>

# First unpack the image
./magiskboot --unpack $BOOTIMAGE

# In normal cases, after unpacking you should get at least kernel and ramdisk.cpio

# Patch ramdisk
./magiskboot --cpio ramdisk.cpio \
"mkdir 000 .backup" \          # create a folder to store our init backup
"mv init .backup/init" \       # backup the original init
"add 750 init magiskinit"      # replace init with magiskinit

# Patch kernel to always use ramdisk as rootfs
# You only need to do this on system-as-root devices
./magiskboot --hexpatch kernel \
736B69705F696E697472616D6673 \
77616E745F696E697472616D6673

# Repack the boot image
./magiskboot --repack $BOOTIMAGE

# The patched image should be located in new-boot.img

System Only

WIP

# Currently not available

Exploits

(Note: Magisk could only be used as root)

Occasionally, there would be exploits in certain devices that could lead to full fledged root. On modern Android, it is possible to use MagiskSU if you can gain a shell with the following conditions:

• Effective UID should be privileged (root, or euid=0)
• Have the ability to reload sepolicy (which 99.9% of the time means SELinux permissive)

Once you got a proper root shell, you should have magiskinit somewhere on the device. The basic idea is try to live patch sepolicy with magiskpolicy, and start magiskd with magisk --daemon. Here are some examples you could use as a reference.

If dm-verity is enforced (no system r/w allowed)

# Assume magiskinit is in current directory
# All commands are required to run on each reboot

# Live patch selinux
ln -s ./magiskinit magiskpolicy
./magiskpolicy --live --magisk "allow magisk * * *"

# Mount tmpfs to /sbin
mount -t tmpfs tmpfs /sbin
chmod 755 /sbin
chcon u:object_r:magisk_file:s0 /sbin

# Add files to /sbin
./magiskinit -x magisk /sbin/magisk
cp -a magiskpolicy /sbin
/sbin/magisk --install /sbin

# Launch magisk daemon
/sbin/magisk --daemon

# (Optional) switch back to enforced
setenforce 1

If dm-verity is not enforced (can modify system)

# Assume magiskinit is in current directory
# The following commands should only need to run once

# Mount system rw
mount -o rw,remount /system

# Add files to system
./magiskinit -x magisk /system/xbin/magisk
cp -a magiskinit /system/xbin
ln -s /system/xbin/magiskinit /system/xbin/magiskpolicy
/system/xbin/magisk --install /system/xbin

# The following commands should run on each reboot
/system/xbin/magiskpolicy --live --magisk "allow magisk * * *"
/system/xbin/magisk --daemon