seccomp: Make seccomp filter reusable

This patchset introduces a new operation and a new flag
to split the SECCOMP_SET_MODE_FILTER process into two steps:
load filter and attach filter. Thus we can reuse the filter.

The new SECCOMP_LOAD_FILTER loads the filter and returns a fd
which can be pinned to bpffs. This extends the lifetime of the
filter and thus can be reused by different processes.
With this new operation, we can eliminate a hot path of JITing
BPF program (the filter) where we apply the same seccomp filter
to thousands of micro VMs on a bare metal instance.

The new flag SECCOMP_FILTER_FLAG_BPF_PROG_FD is used to attach
a filter which is loaded via SECCOMP_LOAD_FILTER and represented
by a seccomp bpf prog fd. The fd is either returned from
SECCOMP_LOAD_FILTER or obtained from bpffs using bpf syscall.

Change logs:
  v1 -> v2:
    - Add a flag to attach filter from fd
    - Update selftests

  RFC -> v1:
    - Addressed comments from Kees
    - Reuse filter copy/create code (patch 1)
    - Add a selftest (patch 4)

Hengqi Chen (5):
  seccomp: Refactor filter copy/create for reuse
  seccomp, bpf: Introduce SECCOMP_LOAD_FILTER operation
  seccomp: Introduce new flag SECCOMP_FILTER_FLAG_BPF_PROG_FD
  selftests/seccomp: Test seccomp filter load and attach
  selftests/bpf: Skip BPF_PROG_TYPE_SECCOMP-related tests

 include/linux/seccomp.h                       |   3 +-
 include/uapi/linux/bpf.h                      |   1 +
 include/uapi/linux/seccomp.h                  |   3 +
 kernel/seccomp.c                              | 170 +++++++++++++++---
 tools/include/uapi/linux/bpf.h                |   1 +
 .../selftests/bpf/prog_tests/libbpf_probes.c  |   3 +-
 .../selftests/bpf/prog_tests/libbpf_str.c     |   3 +
 tools/testing/selftests/seccomp/seccomp_bpf.c |  44 +++++
 8 files changed, 197 insertions(+), 31 deletions(-)

-- 
2.34.1