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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.enabled". By default, it is enabled, but can be disabled at
boot ("loadpin.enabled=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.)