[PATCH bpf-next v2 0/9] Introduce load-acquire and store-release BPF instructions

[Peilin Ye]

Hi all!

This patchset adds kernel support for BPF load-acquire and store-release
instructions (for background, please see [1]), mainly including
core/verifier, arm64 JIT compiler, and Documentation/ changes.  x86-64
and riscv64 are also planned to be supported.  The corresponding LLVM
changes can be found at:
  https://github.com/llvm/llvm-project/pull/108636

An atomic load/store is a BPF_STX | BPF_ATOMIC instruction, with the
lowest 8 bits of the 'imm' field in the following format:

  +-+-+-+-+-+-+-+-+
  | type  | order |
  +-+-+-+-+-+-+-+-+

  o 'type' indicates ATOMIC_LOAD (0x1) or ATOMIC_STORE (0x2)
  o 'order' is one of RELAXED (0x0), ACQUIRE (0x1), RELEASE (0x2),
    ACQ_REL (0x3, acquire-and-release) and SEQ_CST (0x4, sequentially
    consistent)

Currently only two combinations are legal:

  o LOAD_ACQ (0x11: ATOMIC_LOAD, ACQUIRE)
  o STORE_REL (0x22: ATOMIC_STORE, RELEASE)

During v1 there was a discussion on whether it is necessary to have a
dedicated 'order' field and define all possible values, considering that
we only allow two combinations at the moment.  Please refer to [2] for
more context.

v1: https://lore.kernel.org/all/cover.1737763916.git.yepeilin@xxxxxxxxxx/
v1..v2 notable changes:

  o (Eduard) for x86 and s390, make
             bpf_jit_supports_insn(..., /*in_arena=*/true) return false
	     for load_acq/store_rel
  o add Eduard's Acked-by: tag
  o (Eduard) extract LDX and non-ATOMIC STX handling into helpers, see
             PATCH v2 3/9
  o allow unpriv programs to store-release pointers to stack
  o (Alexei) make it clearer in the interpreter code (PATCH v2 4/9) that
             only W and DW are supported for atomic RMW
  o test misaligned load_acq/store_rel
  o (Eduard) other selftests/ changes:
    * test load_acq/store_rel with !atomic_ptr_type_ok() pointers:
      - PTR_TO_CTX, for is_ctx_reg()
      - PTR_TO_PACKET, for is_pkt_reg()
      - PTR_TO_FLOW_KEYS, for is_flow_key_reg()
      - PTR_TO_SOCKET, for is_sk_reg()
    * drop atomics/ tests
    * delete unnecessary 'pid' checks from arena_atomics/ tests
    * avoid depending on __BPF_FEATURE_LOAD_ACQ_STORE_REL, use
      __imm_insn() and inline asm macros instead

RFC v1: https://lore.kernel.org/all/cover.1734742802.git.yepeilin@xxxxxxxxxx
RFC v1..v1 notable changes:

  o 1-2/8: minor verifier.c refactoring patches
  o   3/8: core/verifier changes
         * (Eduard) handle load-acquire properly in backtrack_insn()
         * (Eduard) avoid skipping checks (e.g.,
                    bpf_jit_supports_insn()) for load-acquires
         * track the value stored by store-releases, just like how
           non-atomic STX instructions are handled
         * (Eduard) add missing link in commit message
         * (Eduard) always print 'r' for disasm.c changes
  o   4/8: arm64/insn: avoid treating load_acq/store_rel as
           load_ex/store_ex
  o   5/8: arm64/insn: add load_acq/store_rel
         * (Xu) include Should-Be-One (SBO) bits in "mask" and "value",
                to avoid setting fixed bits during runtime (JIT-compile
                time)
  o   6/8: arm64 JIT compiler changes
         * (Xu) use emit_a64_add_i() for "pointer + offset" to optimize
                code emission
  o   7/8: selftests
         * (Eduard) avoid adding new tests to the 'test_verifier' runner
         * add more tests, e.g., checking mark_precise logic
  o   8/8: instruction-set.rst changes

Please see the individual kernel patches (and LLVM commits) for details.
The LLVM GitHub PR will be split into three (each containing a single
commit) soon.  Feedback is much appreciated!

[1] https://lore.kernel.org/all/20240729183246.4110549-1-yepeilin@xxxxxxxxxx/
[2] https://lore.kernel.org/bpf/Z5srM--fdH_JAgYT@xxxxxxxxxx

Thanks,
Peilin Ye (9):
  bpf/verifier: Factor out atomic_ptr_type_ok()
  bpf/verifier: Factor out check_atomic_rmw()
  bpf/verifier: Factor out check_load_mem() and check_store_reg()
  bpf: Introduce load-acquire and store-release instructions
  arm64: insn: Add BIT(23) to {load,store}_ex's mask
  arm64: insn: Add load-acquire and store-release instructions
  bpf, arm64: Support load-acquire and store-release instructions
  selftests/bpf: Add selftests for load-acquire and store-release
    instructions
  bpf, docs: Update instruction-set.rst for load-acquire and
    store-release instructions

 .../bpf/standardization/instruction-set.rst   | 114 ++++++--
 arch/arm64/include/asm/insn.h                 |  12 +-
 arch/arm64/lib/insn.c                         |  29 ++
 arch/arm64/net/bpf_jit.h                      |  20 ++
 arch/arm64/net/bpf_jit_comp.c                 |  87 +++++-
 arch/s390/net/bpf_jit_comp.c                  |  14 +-
 arch/x86/net/bpf_jit_comp.c                   |   4 +
 include/linux/bpf.h                           |  11 +
 include/linux/filter.h                        |   2 +
 include/uapi/linux/bpf.h                      |  13 +
 kernel/bpf/core.c                             |  63 ++++-
 kernel/bpf/disasm.c                           |  12 +
 kernel/bpf/verifier.c                         | 234 +++++++++++-----
 tools/include/uapi/linux/bpf.h                |  13 +
 .../selftests/bpf/prog_tests/arena_atomics.c  |  50 ++++
 .../selftests/bpf/prog_tests/verifier.c       |   4 +
 .../selftests/bpf/progs/arena_atomics.c       |  88 ++++++
 .../bpf/progs/verifier_load_acquire.c         | 190 +++++++++++++
 .../selftests/bpf/progs/verifier_precision.c  |  47 ++++
 .../bpf/progs/verifier_store_release.c        | 262 ++++++++++++++++++
 20 files changed, 1164 insertions(+), 105 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_load_acquire.c
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_store_release.c

-- 
2.48.1.502.g6dc24dfdaf-goog