1=======
2LoadPin
3=======
4
5LoadPin is a Linux Security Module that ensures all kernel-loaded files
6(modules, firmware, etc) all originate from the same filesystem, with
7the expectation that such a filesystem is backed by a read-only device
8such as dm-verity or CDROM. This allows systems that have a verified
9and/or unchangeable filesystem to enforce module and firmware loading
10restrictions without needing to sign the files individually.
11
12The LSM is selectable at build-time with ``CONFIG_SECURITY_LOADPIN``, and
13can be controlled at boot-time with the kernel command line option
14"``loadpin.enabled``". By default, it is enabled, but can be disabled at
15boot ("``loadpin.enabled=0``").
16
17LoadPin starts pinning when it sees the first file loaded. If the
18block device backing the filesystem is not read-only, a sysctl is
19created to toggle pinning: ``/proc/sys/kernel/loadpin/enabled``. (Having
20a mutable filesystem means pinning is mutable too, but having the
21sysctl allows for easy testing on systems with a mutable filesystem.)
22
23It's also possible to exclude specific file types from LoadPin using kernel
24command line option "``loadpin.exclude``". By default, all files are
25included, but they can be excluded using kernel command line option such
26as "``loadpin.exclude=kernel-module,kexec-image``". This allows to use
27different mechanisms such as ``CONFIG_MODULE_SIG`` and
28``CONFIG_KEXEC_VERIFY_SIG`` to verify kernel module and kernel image while
29still use LoadPin to protect the integrity of other files kernel loads. The
30full list of valid file types can be found in ``kernel_read_file_str``
31defined in ``include/linux/fs.h``.
32