When LSE atomics are available, BPF atomic instructions are implemented as single ARM64 atomic instructions, therefore it is easy to enable these in bpf_arena using the currently available exception handling setup.

LL_SC atomics use loops and therefore would need more work to enable in bpf_arena.

Enable LSE atomics based instructions in bpf_arena and use the bpf_jit_supports_insn() callback to reject atomics in bpf_arena if LSE atomics are not available.

All atomics and arena_atomics selftests are passing:

[root@ip-172-31-2-216 bpf]# ./test_progs -a atomics,arena_atomics #3/1 arena_atomics/add:OK #3/2 arena_atomics/sub:OK #3/3 arena_atomics/and:OK #3/4 arena_atomics/or:OK #3/5 arena_atomics/xor:OK #3/6 arena_atomics/cmpxchg:OK #3/7 arena_atomics/xchg:OK #3 arena_atomics:OK #10/1 atomics/add:OK #10/2 atomics/sub:OK #10/3 atomics/and:OK #10/4 atomics/or:OK #10/5 atomics/xor:OK #10/6 atomics/cmpxchg:OK #10/7 atomics/xchg:OK #10 atomics:OK Summary: 2/14 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Puranjay Mohan puranjay@kernel.org --- arch/arm64/net/bpf_jit_comp.c | 48 ++++++++++++++++---- tools/testing/selftests/bpf/DENYLIST.aarch64 | 1 - 2 files changed, 40 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index 76b91f36c729..53347d4217f4 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -494,20 +494,26 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx) static int emit_lse_atomic(const struct bpf_insn *insn, struct jit_ctx *ctx) { const u8 code = insn->code; + const u8 arena_vm_base = bpf2a64[ARENA_VM_START]; const u8 dst = bpf2a64[insn->dst_reg]; const u8 src = bpf2a64[insn->src_reg]; const u8 tmp = bpf2a64[TMP_REG_1]; const u8 tmp2 = bpf2a64[TMP_REG_2]; const bool isdw = BPF_SIZE(code) == BPF_DW; + const bool arena = BPF_MODE(code) == BPF_PROBE_ATOMIC; const s16 off = insn->off; - u8 reg; + u8 reg = dst;

- if (!off) { - reg = dst; - } else { - emit_a64_mov_i(1, tmp, off, ctx); - emit(A64_ADD(1, tmp, tmp, dst), ctx); - reg = tmp; + if (off || arena) { + if (off) { + emit_a64_mov_i(1, tmp, off, ctx); + emit(A64_ADD(1, tmp, tmp, dst), ctx); + reg = tmp; + } + if (arena) { + emit(A64_ADD(1, tmp, reg, arena_vm_base), ctx); + reg = tmp; + } }

switch (insn->imm) { @@ -576,6 +582,12 @@ static int emit_ll_sc_atomic(const struct bpf_insn *insn, struct jit_ctx *ctx) u8 reg; s32 jmp_offset;

+ if (BPF_MODE(code) == BPF_PROBE_ATOMIC) { + /* ll_sc based atomics don't support unsafe pointers yet. */ + pr_err_once("unknown atomic opcode %02x\n", code); + return -EINVAL; + } + if (!off) { reg = dst; } else { @@ -777,7 +789,8 @@ static int add_exception_handler(const struct bpf_insn *insn,

if (BPF_MODE(insn->code) != BPF_PROBE_MEM && BPF_MODE(insn->code) != BPF_PROBE_MEMSX && - BPF_MODE(insn->code) != BPF_PROBE_MEM32) + BPF_MODE(insn->code) != BPF_PROBE_MEM32 && + BPF_MODE(insn->code) != BPF_PROBE_ATOMIC) return 0;

if (!ctx->prog->aux->extable || @@ -1474,12 +1487,18 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,

case BPF_STX | BPF_ATOMIC | BPF_W: case BPF_STX | BPF_ATOMIC | BPF_DW: + case BPF_STX | BPF_PROBE_ATOMIC | BPF_W: + case BPF_STX | BPF_PROBE_ATOMIC | BPF_DW: if (cpus_have_cap(ARM64_HAS_LSE_ATOMICS)) ret = emit_lse_atomic(insn, ctx); else ret = emit_ll_sc_atomic(insn, ctx); if (ret) return ret; + + ret = add_exception_handler(insn, ctx, dst); + if (ret) + return ret; break;

default: @@ -2527,6 +2546,19 @@ bool bpf_jit_supports_arena(void) return true; }

+bool bpf_jit_supports_insn(struct bpf_insn *insn, bool in_arena) +{ + if (!in_arena) + return true; + switch (insn->code) { + case BPF_STX | BPF_ATOMIC | BPF_W: + case BPF_STX | BPF_ATOMIC | BPF_DW: + if (!cpus_have_cap(ARM64_HAS_LSE_ATOMICS)) + return false; + } + return true; +} + void bpf_jit_free(struct bpf_prog *prog) { if (prog->jited) { diff --git a/tools/testing/selftests/bpf/DENYLIST.aarch64 b/tools/testing/selftests/bpf/DENYLIST.aarch64 index cf657fc35619..0445ac38bc07 100644 --- a/tools/testing/selftests/bpf/DENYLIST.aarch64 +++ b/tools/testing/selftests/bpf/DENYLIST.aarch64 @@ -10,4 +10,3 @@ fill_link_info/kprobe_multi_link_info # bpf_program__attach_kprobe_mu fill_link_info/kretprobe_multi_link_info # bpf_program__attach_kprobe_multi_opts unexpected error: -95 fill_link_info/kprobe_multi_invalid_ubuff # bpf_program__attach_kprobe_multi_opts unexpected error: -95 missed/kprobe_recursion # missed_kprobe_recursion__attach unexpected error: -95 (errno 95) -arena_atomics