This patchset introduces safe dynamic LSM support. It does this via SRCU-protected security hooks. It also EXPORT_SYMBOL_GPLs the symbols required to perform runtime loading, and unloading. The patchset is meant to introduce as little overhead as possible when not used. Additionally, the functionality is disabled by default.
The SRCU was made safe to call from an interrupt context in the patch "srcu: Allow use of Classic SRCU from both process and interrupt context" (1123a6041654e8f889014659593bad4168e542c2) by Paolo Bonzini. Therefore this mechanism is safe to use for traversal of the callback list, even when a hook is called from the interrupt context. Currently, this maintains an entirely seperate mechanism to attach hooks because the hooks are behind managed static_keys to prevent overhead. This is also done so sealable memory support could be added at a later point. The callbacks currently include a percpu_counter, but that could sit outside of the struct itself. This may also have a benefit that these counters, could have __cacheline_aligned_in_smp. Although, in my testing I was unable to find much performance delta with percpu_counters that were not aligned. It includes an example LSM that prevents specific time travel. Sargun Dhillon (3): security: Add safe, dynamic (runtime-loadable) hook support LSM: Add statistics about the invocation of dynamic hooks LSM: Add an example sample dynamic LSM include/linux/lsm_hooks.h | 254 +++++++++++++++++++++++++++++++++++++ samples/Kconfig | 6 + samples/Makefile | 2 +- samples/lsm/Makefile | 4 + samples/lsm/lsm_example.c | 46 +++++++ security/Kconfig | 16 +++ security/Makefile | 2 + security/dynamic.c | 316 ++++++++++++++++++++++++++++++++++++++++++++++ security/dynamic.h | 33 +++++ security/dynamicfs.c | 118 +++++++++++++++++ security/inode.c | 2 + security/security.c | 66 +++++++++- 12 files changed, 863 insertions(+), 2 deletions(-) create mode 100644 samples/lsm/Makefile create mode 100644 samples/lsm/lsm_example.c create mode 100644 security/dynamic.c create mode 100644 security/dynamic.h create mode 100644 security/dynamicfs.c -- 2.9.3
