[PATCH v4 bpf-next 0/2] bpf: refine kernel.unprivileged_bpf_disabled behaviour

[Alan Maguire <alan.maguire@oracle.com>]

Unprivileged BPF disabled (kernel.unprivileged_bpf_disabled >= 1)
is the default in most cases now; when set, the BPF system call is
blocked for users without CAP_BPF/CAP_SYS_ADMIN.  In some cases
however, it makes sense to split activities between capability-requiring
ones - such as program load/attach - and those that might not require
capabilities such as reading perf/ringbuf events, reading or
updating BPF map configuration etc.  One example of this sort of
approach is a service that loads a BPF program, and a user-space
program that interacts with it.

Here - rather than blocking all BPF syscall commands - unprivileged
BPF disabled blocks the key object-creating commands (prog load,
map load).  Discussion has alluded to this idea in the past [1],
and Alexei mentioned it was also discussed at LSF/MM/BPF this year.

Changes since v3 [2]:
- added acks to patch 1
- CI was failing on Ubuntu; I suspect the issue was an old capability.h
  file which specified CAP_LAST_CAP as < CAP_BPF, leading to the logic
  disabling all caps not disabling CAP_BPF.  Use CAP_BPF as basis for
  "all caps" bitmap instead as we explicitly define it in cap_helpers.h
  if not already found in capabilities.h
- made global variables arguments to subtests instead (Andrii, patch 2)

Changes since v2 [3]:

- added acks from Yonghong
- clang compilation issue in selftest with bpf_prog_query()
  (Alexei, patch 2)
- disable all capabilities for test (Yonghong, patch 2)
- add assertions that size of perf/ringbuf data matches expectations
  (Yonghong, patch 2)
- add map array size definition, remove unneeded whitespace (Yonghong, patch 2)

Changes since RFC [4]:

- widened scope of commands unprivileged BPF disabled allows
  (Alexei, patch 1)
- removed restrictions on map types for lookup, update, delete
  (Alexei, patch 1)
- removed kernel CONFIG parameter controlling unprivileged bpf disabled
  change (Alexei, patch 1)
- widened test scope to cover most BPF syscall commands, with positive
  and negative subtests

[1] https://lore.kernel.org/bpf/CAADnVQLTBhCTAx1a_nev7CgMZxv1Bb7ecz1AFRin8tHmjPREJA@mail.gmail.com/
[2] https://lore.kernel.org/bpf/1652880861-27373-1-git-send-email-alan.maguire@oracle.com/T/
[3] https://lore.kernel.org/bpf/1652788780-25520-1-git-send-email-alan.maguire@oracle.com/T/#t
[4] https://lore.kernel.org/bpf/20220511163604.5kuczj6jx3ec5qv6@MBP-98dd607d3435.dhcp.thefacebook.com/T/#mae65f35a193279e718f37686da636094d69b96ee

Alan Maguire (2):
  bpf: refine kernel.unprivileged_bpf_disabled behaviour
  selftests/bpf: add tests verifying unprivileged bpf behaviour

 kernel/bpf/syscall.c                          |  14 +-
 .../bpf/prog_tests/unpriv_bpf_disabled.c      | 312 ++++++++++++++++++
 .../bpf/progs/test_unpriv_bpf_disabled.c      |  83 +++++
 3 files changed, 408 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/unpriv_bpf_disabled.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_unpriv_bpf_disabled.c

-- 
2.27.0