xref: /kernel/linux/linux-6.6/Documentation/admin-guide/LSM/LoadPin.rst

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LoadPin
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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.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``.