LoadPin is a Linux Security Module that ensures all kernel-loaded files (modules, firmware, etc) all originate from the same filesystem, with the expectation that such a filesystem is backed by a read-only device such as dm-verity or CDROM. This allows systems that have a verified and/or unchangeable filesystem to enforce module and firmware loading restrictions without needing to sign the files individually.

The LSM is selectable at build-time with CONFIG_SECURITY_LOADPIN, and can be controlled at boot-time with the kernel command line option “loadpin.enforce”. By default, it is enabled, but can be disabled at boot (”loadpin.enforce=0”).

LoadPin starts pinning when it sees the first file loaded. If the block device backing the filesystem is not read-only, a sysctl is created to toggle pinning: /proc/sys/kernel/loadpin/enabled. (Having a mutable filesystem means pinning is mutable too, but having the sysctl allows for easy testing on systems with a mutable filesystem.)

It’s also possible to exclude specific file types from LoadPin using kernel command line option “loadpin.exclude”. By default, all files are included, but they can be excluded using kernel command line option such as “loadpin.exclude=kernel-module,kexec-image”. This allows to use different mechanisms such as CONFIG_MODULE_SIG and CONFIG_KEXEC_VERIFY_SIG to verify kernel module and kernel image while still use LoadPin to protect the integrity of other files kernel loads. The full list of valid file types can be found in kernel_read_file_str defined in include/linux/kernel_read_file.h.