Safe, dynamically loadable LSM hooks

This patchset introduces safe dynamic LSM support. These are currently not unloadable, until we figure out a use case that needs that. Adding an unload hook is trivial given the way the patch is written.

This exposes a second mechanism of loading hooks which are in modules. These hooks are behind static keys, so they should come at low performance overhead. The built-in hook heads are read-only, whereas the dynamic hooks are mutable.

Not all hooks can be loaded into. Some hooks are blacklisted, and therefore trying to load a module which plugs into those hooks will fail.

One of the big benefits with loadable security modules is to help with "unknown unknowns". Although, livepatch is excellent, sometimes, a surgical LSM is simpler.

It includes an example LSM that prevents specific time travel.

Changes since v3:
* readded hook blacklisted
* return error, rather than panic if unable to allocate memory

Changes since v2:
* inode get/set security is readded
* xfrm singleton hook readded
* Security hooks are turned into an array
* Security hooks and dynamic hooks enum is collapsed

Changes since v1:
* It no longer allows unloading of modules
* prctl is fixed
* inode get/set security is removed
* xfrm singleton hook removed

Sargun Dhillon (3):
security: Refactor LSM hooks into an array and enum
security: Expose a mechanism to load lsm hooks dynamically at runtime
security: Add an example sample dynamic LSM

 include/linux/lsm_hooks.h | 459 ++++++++++++++++++++++++----------------------
 samples/Kconfig           |   6 +
 samples/Makefile          |   2 +-
 samples/lsm/Makefile      |   4 +
 samples/lsm/lsm_example.c |  33 ++++
 security/Kconfig          |   9 +
 security/inode.c          |  13 +-
 security/security.c       | 222 ++++++++++++++++++++--
 8 files changed, 508 insertions(+), 240 deletions(-)
 create mode 100644 samples/lsm/Makefile
 create mode 100644 samples/lsm/lsm_example.c

2.14.1

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