bpf/verifier: Handle BPF_LOAD_ACQ instructions in insn_def_regno()

In preparation for supporting BPF load-acquire and store-release
instructions for architectures where bpf_jit_needs_zext() returns true
(e.g. riscv64), make insn_def_regno() handle load-acquires properly.

Acked-by: Björn Töpel <bjorn@kernel.org>
Tested-by: Björn Töpel <bjorn@rivosinc.com> # QEMU/RVA23
Signed-off-by: Peilin Ye <yepeilin@google.com>
Reviewed-by: Pu Lehui <pulehui@huawei.com>
Link: https://lore.kernel.org/r/09cb2aec979aaed9d16db41f0f5b364de39377c0.1746588351.git.yepeilin@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: peilin-ye

kernel/bpf/verifier.c

@@ -3649,16 +3649,16 @@ static int insn_def_regno(const struct bpf_insn *insn)
 	case BPF_ST:
 		return -1;
 	case BPF_STX:
-		if ((BPF_MODE(insn->code) == BPF_ATOMIC ||
-		     BPF_MODE(insn->code) == BPF_PROBE_ATOMIC) &&
-		    (insn->imm & BPF_FETCH)) {
+		if (BPF_MODE(insn->code) == BPF_ATOMIC ||
+		    BPF_MODE(insn->code) == BPF_PROBE_ATOMIC) {
 			if (insn->imm == BPF_CMPXCHG)
 				return BPF_REG_0;
-			else
+			else if (insn->imm == BPF_LOAD_ACQ)
+				return insn->dst_reg;
+			else if (insn->imm & BPF_FETCH)
 				return insn->src_reg;
-		} else {
-			return -1;
 		}
+		return -1;
 	default:
 		return insn->dst_reg;
 	}