bpf: Search and add kfuncs in struct_ops prologue and epilogue

Currently, add_kfunc_call() is only invoked once before the main
verification loop. Therefore, the verifier could not find the
bpf_kfunc_btf_tab of a new kfunc call which is not seen in user defined
struct_ops operators but introduced in gen_prologue or gen_epilogue
during do_misc_fixup(). Fix this by searching kfuncs in the patching
instruction buffer and add them to prog->aux->kfunc_tab.

Signed-off-by: Amery Hung <[e-mail]>
Acked-by: Eduard Zingerman <[e-mail]>
Acked-by: Martin KaFai Lau <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

kernel/bpf/verifier.c

···
 	return res ? &res->func_model : NULL;
 }
 
+static int add_kfunc_in_insns(struct bpf_verifier_env *env,
+			      struct bpf_insn *insn, int cnt)
+{
+	int i, ret;
+
+	for (i = 0; i < cnt; i++, insn++) {
+		if (bpf_pseudo_kfunc_call(insn)) {
+			ret = add_kfunc_call(env, insn->imm, insn->off);
+			if (ret < 0)
+				return ret;
+		}
+	}
+	return 0;
+}
+
 static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
 {
 	struct bpf_subprog_info *subprog = env->subprog_info;
···
 {
 	struct bpf_subprog_info *subprogs = env->subprog_info;
 	const struct bpf_verifier_ops *ops = env->ops;
-	int i, cnt, size, ctx_field_size, delta = 0, epilogue_cnt = 0;
+	int i, cnt, size, ctx_field_size, ret, delta = 0, epilogue_cnt = 0;
 	const int insn_cnt = env->prog->len;
 	struct bpf_insn *epilogue_buf = env->epilogue_buf;
 	struct bpf_insn *insn_buf = env->insn_buf;
···
 				return -ENOMEM;
 			env->prog = new_prog;
 			delta += cnt - 1;
+
+			ret = add_kfunc_in_insns(env, epilogue_buf, epilogue_cnt - 1);
+			if (ret < 0)
+				return ret;
 		}
 	}
 
···
 
 			env->prog = new_prog;
 			delta += cnt - 1;
+
+			ret = add_kfunc_in_insns(env, insn_buf, cnt - 1);
+			if (ret < 0)
+				return ret;
 		}
 	}