bpf: recognize 64bit immediate loads as consts

When running as parser interpret BPF_LD | BPF_IMM | BPF_DW
instructions as loading CONST_IMM with the value stored
in imm.  The verifier will continue not recognizing those
due to concerns about search space/program complexity
increase.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/bpf/verifier.c

@@ -1769,10 +1769,20 @@ static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn)
 	if (err)
 		return err;
 
-	if (insn->src_reg == 0)
-		/* generic move 64-bit immediate into a register */
+	if (insn->src_reg == 0) {
+		/* generic move 64-bit immediate into a register,
+		 * only analyzer needs to collect the ld_imm value.
+		 */
+		u64 imm = ((u64)(insn + 1)->imm << 32) | (u32)insn->imm;
+
+		if (!env->analyzer_ops)
 			return 0;
 
+		regs[insn->dst_reg].type = CONST_IMM;
+		regs[insn->dst_reg].imm = imm;
+		return 0;
+	}
+
 	/* replace_map_fd_with_map_ptr() should have caught bad ld_imm64 */
 	BUG_ON(insn->src_reg != BPF_PSEUDO_MAP_FD);