[RFC PATCH -mm 0/4] mm, security, bpf: Fine-grained control over memory policy adjustments with lsm bpf

[Yafang Shao]

Background
==========

In our containerized environment, we've identified unexpected OOM events
where the OOM-killer terminates tasks despite having ample free memory.
This anomaly is traced back to tasks within a container using mbind(2) to
bind memory to a specific NUMA node. When the allocated memory on this node
is exhausted, the OOM-killer, prioritizing tasks based on oom_score,
indiscriminately kills tasks. This becomes more critical with guaranteed
tasks (oom_score_adj: -998) aggravating the issue.

The selected victim might not have allocated memory on the same NUMA node,
rendering the killing ineffective. This patch aims to address this by
disabling MPOL_BIND in container environments.

In the container environment, our aim is to consolidate memory resource
control under the management of kubelet. If users express a preference for
binding their memory to a specific NUMA node, we encourage the adoption of
a standardized approach. Specifically, we recommend configuring this memory
policy through kubelet using cpuset.mems in the cpuset controller, rather
than individual users setting it autonomously. This centralized approach
ensures that NUMA nodes are globally managed through kubelet, promoting
consistency and facilitating streamlined administration of memory resources
across the entire containerized environment.

Proposed Solutions
=================

- Introduce Capability to Disable MPOL_BIND
  Currently, any task can perform MPOL_BIND without specific capabilities.
  Enforcing CAP_SYS_RESOURCE or CAP_SYS_NICE could be an option, but this
  may have unintended consequences. Capabilities, being broad, might grant
  unnecessary privileges. We should explore alternatives to prevent
  unexpected side effects.

- Use LSM BPF to Disable MPOL_BIND
  Introduce LSM hooks for syscalls such as mbind(2), set_mempolicy(2), and
  set_mempolicy_home_node(2) to disable MPOL_BIND. This approach is more
  flexibility and allows for fine-grained control without unintended
  consequences. A sample LSM BPF program is included, demonstrating
  practical implementation in a production environment.

Future Considerations
=====================

In addition, there's room for enhancement in the OOM-killer for cases
involving CONSTRAINT_MEMORY_POLICY. It would be more beneficial to
prioritize selecting a victim that has allocated memory on the same NUMA
node. My exploration on the lore led me to a proposal[0] related to this
matter, although consensus seems elusive at this point. Nevertheless,
delving into this specific topic is beyond the scope of the current
patchset.

[0]. https://lore.kernel.org/lkml/20220512044634.63586-1-ligang.bdlg@bytedance.com/ 

Yafang Shao (4):
  mm, security: Add lsm hook for mbind(2)
  mm, security: Add lsm hook for set_mempolicy(2)
  mm, security: Add lsm hook for set_mempolicy_home_node(2)
  selftests/bpf: Add selftests for mbind(2) with lsm prog

 include/linux/lsm_hook_defs.h                      |  8 +++
 include/linux/security.h                           | 26 +++++++
 mm/mempolicy.c                                     | 13 ++++
 security/security.c                                | 19 ++++++
 tools/testing/selftests/bpf/prog_tests/mempolicy.c | 79 ++++++++++++++++++++++
 tools/testing/selftests/bpf/progs/test_mempolicy.c | 29 ++++++++
 6 files changed, 174 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/mempolicy.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_mempolicy.c

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1.8.3.1