bpf: reuse subprog argument parsing logic for subprog call checks

Remove duplicated BTF parsing logic when it comes to subprog call check.
Instead, use (potentially cached) results of btf_prepare_func_args() to
abstract away expectations of each subprog argument in generic terms
(e.g., "this is pointer to context", or "this is a pointer to memory of
size X"), and then use those simple high-level argument type
expectations to validate actual register states to check if they match
expectations.

Acked-by: Eduard Zingerman <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

kernel/bpf/verifier.c

···
 	return err;
 }
 
-static int btf_check_func_arg_match(struct bpf_verifier_env *env,
-				    const struct btf *btf, u32 func_id,
-				    struct bpf_reg_state *regs,
-				    bool ptr_to_mem_ok)
+static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
+				    const struct btf *btf,
+				    struct bpf_reg_state *regs)
 {
-	enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
+	struct bpf_subprog_info *sub = subprog_info(env, subprog);
 	struct bpf_verifier_log *log = &env->log;
-	const char *func_name, *ref_tname;
-	const struct btf_type *t, *ref_t;
-	const struct btf_param *args;
-	u32 i, nargs, ref_id;
+	u32 i;
 	int ret;
 
-	t = btf_type_by_id(btf, func_id);
-	if (!t || !btf_type_is_func(t)) {
-		/* These checks were already done by the verifier while loading
-		 * struct bpf_func_info or in add_kfunc_call().
-		 */
-		bpf_log(log, "BTF of func_id %u doesn't point to KIND_FUNC\n",
-			func_id);
-		return -EFAULT;
-	}
-	func_name = btf_name_by_offset(btf, t->name_off);
-
-	t = btf_type_by_id(btf, t->type);
-	if (!t || !btf_type_is_func_proto(t)) {
-		bpf_log(log, "Invalid BTF of func %s\n", func_name);
-		return -EFAULT;
-	}
-	args = (const struct btf_param *)(t + 1);
-	nargs = btf_type_vlen(t);
-	if (nargs > MAX_BPF_FUNC_REG_ARGS) {
-		bpf_log(log, "Function %s has %d > %d args\n", func_name, nargs,
-			MAX_BPF_FUNC_REG_ARGS);
-		return -EINVAL;
-	}
+	ret = btf_prepare_func_args(env, subprog);
+	if (ret)
+		return ret;
 
 	/* check that BTF function arguments match actual types that the
 	 * verifier sees.
 	 */
-	for (i = 0; i < nargs; i++) {
-		enum bpf_arg_type arg_type = ARG_DONTCARE;
+	for (i = 0; i < sub->arg_cnt; i++) {
 		u32 regno = i + 1;
 		struct bpf_reg_state *reg = &regs[regno];
+		struct bpf_subprog_arg_info *arg = &sub->args[i];
 
-		t = btf_type_skip_modifiers(btf, args[i].type, NULL);
-		if (btf_type_is_scalar(t)) {
-			if (reg->type == SCALAR_VALUE)
-				continue;
-			bpf_log(log, "R%d is not a scalar\n", regno);
-			return -EINVAL;
-		}
-
-		if (!btf_type_is_ptr(t)) {
-			bpf_log(log, "Unrecognized arg#%d type %s\n",
-				i, btf_type_str(t));
-			return -EINVAL;
-		}
-
-		ref_t = btf_type_skip_modifiers(btf, t->type, &ref_id);
-		ref_tname = btf_name_by_offset(btf, ref_t->name_off);
-
-		ret = check_func_arg_reg_off(env, reg, regno, arg_type);
-		if (ret < 0)
-			return ret;
-
-		if (btf_get_prog_ctx_type(log, btf, t, prog_type, i)) {
+		if (arg->arg_type == ARG_ANYTHING) {
+			if (reg->type != SCALAR_VALUE) {
+				bpf_log(log, "R%d is not a scalar\n", regno);
+				return -EINVAL;
+			}
+		} else if (arg->arg_type == ARG_PTR_TO_CTX) {
+			ret = check_func_arg_reg_off(env, reg, regno, ARG_DONTCARE);
+			if (ret < 0)
+				return ret;
 			/* If function expects ctx type in BTF check that caller
 			 * is passing PTR_TO_CTX.
 			 */
 			if (reg->type != PTR_TO_CTX) {
-				bpf_log(log,
-					"arg#%d expected pointer to ctx, but got %s\n",
-					i, btf_type_str(t));
+				bpf_log(log, "arg#%d expects pointer to ctx\n", i);
 				return -EINVAL;
 			}
-		} else if (ptr_to_mem_ok) {
-			const struct btf_type *resolve_ret;
-			u32 type_size;
+		} else if (base_type(arg->arg_type) == ARG_PTR_TO_MEM) {
+			ret = check_func_arg_reg_off(env, reg, regno, ARG_DONTCARE);
+			if (ret < 0)
+				return ret;
 
-			resolve_ret = btf_resolve_size(btf, ref_t, &type_size);
-			if (IS_ERR(resolve_ret)) {
-				bpf_log(log,
-					"arg#%d reference type('%s %s') size cannot be determined: %ld\n",
-					i, btf_type_str(ref_t), ref_tname,
-					PTR_ERR(resolve_ret));
-				return -EINVAL;
-			}
-
-			if (check_mem_reg(env, reg, regno, type_size))
+			if (check_mem_reg(env, reg, regno, arg->mem_size))
 				return -EINVAL;
 		} else {
-			bpf_log(log, "reg type unsupported for arg#%d function %s#%d\n", i,
-				func_name, func_id);
-			return -EINVAL;
+			bpf_log(log, "verifier bug: unrecognized arg#%d type %d\n",
+				i, arg->arg_type);
+			return -EFAULT;
 		}
 	}
 
···
  * Only PTR_TO_CTX and SCALAR_VALUE states are recognized.
  */
 static int btf_check_subprog_call(struct bpf_verifier_env *env, int subprog,
-			          struct bpf_reg_state *regs)
+				  struct bpf_reg_state *regs)
 {
 	struct bpf_prog *prog = env->prog;
 	struct btf *btf = prog->aux->btf;
-	bool is_global;
 	u32 btf_id;
 	int err;
 
···
 	if (prog->aux->func_info_aux[subprog].unreliable)
 		return -EINVAL;
 
-	is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
-	err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global);
-
+	err = btf_check_func_arg_match(env, subprog, btf, regs);
 	/* Compiler optimizations can remove arguments from static functions
 	 * or mismatched type can be passed into a global function.
 	 * In such cases mark the function as unreliable from BTF point of view.

tools/testing/selftests/bpf/progs/test_global_func5.c

···
 }
 
 SEC("tc")
-__failure __msg("expected pointer to ctx, but got PTR")
+__failure __msg("expects pointer to ctx")
 int global_func5(struct __sk_buff *skb)
 {
 	return f1(skb) + f2(2, skb) + f3(3, skb);