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
