bpf-lsm: Extend interoperability with IMA

Extend the interoperability with IMA, to give wider flexibility for the
implementation of integrity-focused LSMs based on eBPF.

Patch 1 fixes some style issues.

Patches 2-6 give the ability to eBPF-based LSMs to take advantage of the
measurement capability of IMA without needing to setup a policy in IMA
(those LSMs might implement the policy capability themselves).

Patches 7-9 allow eBPF-based LSMs to evaluate files read by the kernel.

Changelog

v2:
- Add better description to patch 1 (suggested by Shuah)
- Recalculate digest if it is not fresh (when IMA_COLLECTED flag not set)
- Move declaration of bpf_ima_file_hash() at the end (suggested by
  Yonghong)
- Add tests to check if the digest has been recalculated
- Add deny test for bpf_kernel_read_file()
- Add description to tests

v1:
- Modify ima_file_hash() only and allow the usage of the function with the
  modified behavior by eBPF-based LSMs through the new function
  bpf_ima_file_hash() (suggested by Mimi)
- Make bpf_lsm_kernel_read_file() sleepable so that bpf_ima_inode_hash()
  and bpf_ima_file_hash() can be called inside the implementation of
  eBPF-based LSMs for this hook

Roberto Sassu (9):
  ima: Fix documentation-related warnings in ima_main.c
  ima: Always return a file measurement in ima_file_hash()
  bpf-lsm: Introduce new helper bpf_ima_file_hash()
  selftests/bpf: Move sample generation code to ima_test_common()
  selftests/bpf: Add test for bpf_ima_file_hash()
  selftests/bpf: Check if the digest is refreshed after a file write
  bpf-lsm: Make bpf_lsm_kernel_read_file() as sleepable
  selftests/bpf: Add test for bpf_lsm_kernel_read_file()
  selftests/bpf: Check that bpf_kernel_read_file() denies reading IMA
    policy

 include/uapi/linux/bpf.h                      |  11 ++
 kernel/bpf/bpf_lsm.c                          |  21 +++
 security/integrity/ima/ima_main.c             |  57 ++++---
 tools/include/uapi/linux/bpf.h                |  11 ++
 tools/testing/selftests/bpf/ima_setup.sh      |  35 +++-
 .../selftests/bpf/prog_tests/test_ima.c       | 149 +++++++++++++++++-
 tools/testing/selftests/bpf/progs/ima.c       |  66 +++++++-
 7 files changed, 321 insertions(+), 29 deletions(-)

-- 
2.32.0