Subject: [PATCH v2 bpf-next 00/10] bpf: improve verifier scalability

From: Alexei Starovoitov <[email-masked]>
Date: Mon, 1 Apr 2019 21:27:39 -0700

v1->v2:
- fixed typo in patch 1
- added a patch to convert kcalloc to kvcalloc
- added a patch to verbose 16-bit jump offset check
- added a test with 1m insns

This patch set is the first step to be able to accept large programs.
The verifier still suffers from its brute force algorithm and
large programs can easily hit 1M insn_processed limit.
A lot more work is necessary to be able to verify large programs.

v1:
Realize two key ideas to speed up verification speed by ~20 times
1. every 'branching' instructions records all verifier states.
   not all of them are useful for search pruning.
   add a simple heuristic to keep states that were successful in search pruning
   and remove those that were not
2. mark_reg_read walks parentage chain of registers to mark parents as LIVE_READ.
   Once the register is marked there is no need to remark it again in the future.
   Hence stop walking the chain once first LIVE_READ is seen.

1st optimization gives 10x speed up on large programs
and 2nd optimization reduces the cost of mark_reg_read from ~40% of cpu to <1%.
Combined the deliver ~20x speedup on large programs.

Faster and bounded verification time allows to increase insn_processed
limit to 1 million from 130k.
Worst case it takes 1/10 of a second to process that many instructions
and peak memory consumption is peak_states * sizeof(struct bpf_verifier_state)
which is around ~5Mbyte.

Increase insn_per_program limit for root to insn_processed limit.

Add verification stats and stress tests for verifier scalability.

Alexei Starovoitov (10):
  bpf: add verifier stats and log_level bit 2
  bpf: improve verification speed by droping states
  bpf: improve verification speed by not remarking live_read
  bpf: convert temp arrays to kvcalloc
  bpf: verbose jump offset overflow check
  bpf: increase complexity limit and maximum program size
  bpf: increase verifier log limit
  libbpf: teach libbpf about log_level bit 2
  selftests/bpf: add few verifier scale tests
  selftests/bpf: synthetic tests to push verifier limits

 include/linux/bpf.h                           |   1 +
 include/linux/bpf_verifier.h                  |  23 +++
 kernel/bpf/core.c                             |  11 +-
 kernel/bpf/syscall.c                          |   3 +-
 kernel/bpf/verifier.c                         | 153 +++++++++++++-----
 tools/lib/bpf/bpf.c                           |   2 +-
 tools/lib/bpf/bpf.h                           |   2 +-
 tools/lib/bpf/libbpf.c                        |  16 +-
 tools/lib/bpf/libbpf.h                        |   1 +
 .../bpf/prog_tests/bpf_verif_scale.c          |  49 ++++++
 .../testing/selftests/bpf/progs/test_jhash.h  |  70 ++++++++
 .../selftests/bpf/progs/test_verif_scale1.c   |  30 ++++
 .../selftests/bpf/progs/test_verif_scale2.c   |  30 ++++
 .../selftests/bpf/progs/test_verif_scale3.c   |  30 ++++
 tools/testing/selftests/bpf/test_progs.c      |   6 +-
 tools/testing/selftests/bpf/test_progs.h      |   1 +
 tools/testing/selftests/bpf/test_verifier.c   |  35 ++--
 tools/testing/selftests/bpf/verifier/ld_dw.c  |   9 ++
 18 files changed, 415 insertions(+), 57 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_jhash.h
 create mode 100644 tools/testing/selftests/bpf/progs/test_verif_scale1.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_verif_scale2.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_verif_scale3.c

-- 
2.20.0