| ======= | |
| LoadPin | |
| ======= | |
| 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``. |