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