bpf_dummy_struct_ops.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2021. Huawei Technologies Co., Ltd
 */
#include <linux/kernel.h>
#include <linux/bpf_verifier.h>
#include <linux/bpf.h>
#include <linux/btf.h>

static struct bpf_struct_ops bpf_bpf_dummy_ops;

/* A common type for test_N with return value in bpf_dummy_ops */
typedef int (*dummy_ops_test_ret_fn)(struct bpf_dummy_ops_state *state, ...);

static int dummy_ops_test_ret_function(struct bpf_dummy_ops_state *state, ...)
{
	return 0;
}

struct bpf_dummy_ops_test_args {
	u64 args[MAX_BPF_FUNC_ARGS];
	struct bpf_dummy_ops_state state;
};

static struct btf *bpf_dummy_ops_btf;

static struct bpf_dummy_ops_test_args *
dummy_ops_init_args(const union bpf_attr *kattr, unsigned int nr)
{
	__u32 size_in;
	struct bpf_dummy_ops_test_args *args;
	void __user *ctx_in;
	void __user *u_state;

	size_in = kattr->test.ctx_size_in;
	if (size_in != sizeof(u64) * nr)
		return ERR_PTR(-EINVAL);

	args = kzalloc(sizeof(*args), GFP_KERNEL);
	if (!args)
		return ERR_PTR(-ENOMEM);

	ctx_in = u64_to_user_ptr(kattr->test.ctx_in);
	if (copy_from_user(args->args, ctx_in, size_in))
		goto out;

	/* args[0] is 0 means state argument of test_N will be NULL */
	u_state = u64_to_user_ptr(args->args[0]);
	if (u_state && copy_from_user(&args->state, u_state,
				      sizeof(args->state)))
		goto out;

	return args;
out:
	kfree(args);
	return ERR_PTR(-EFAULT);
}

static int dummy_ops_copy_args(struct bpf_dummy_ops_test_args *args)
{
	void __user *u_state;

	u_state = u64_to_user_ptr(args->args[0]);
	if (u_state && copy_to_user(u_state, &args->state, sizeof(args->state)))
		return -EFAULT;

	return 0;
}

static int dummy_ops_call_op(void *image, struct bpf_dummy_ops_test_args *args)
{
	dummy_ops_test_ret_fn test = (void *)image + cfi_get_offset();
	struct bpf_dummy_ops_state *state = NULL;

	/* state needs to be NULL if args[0] is 0 */
	if (args->args[0])
		state = &args->state;
	return test(state, args->args[1], args->args[2],
		    args->args[3], args->args[4]);
}

static const struct bpf_ctx_arg_aux *find_ctx_arg_info(struct bpf_prog_aux *aux, int offset)
{
	int i;

	for (i = 0; i < aux->ctx_arg_info_size; i++)
		if (aux->ctx_arg_info[i].offset == offset)
			return &aux->ctx_arg_info[i];

	return NULL;
}

/* There is only one check at the moment:
 * - zero should not be passed for pointer parameters not marked as nullable.
 */
static int check_test_run_args(struct bpf_prog *prog, struct bpf_dummy_ops_test_args *args)
{
	const struct btf_type *func_proto = prog->aux->attach_func_proto;

	for (u32 arg_no = 0; arg_no < btf_type_vlen(func_proto) ; ++arg_no) {
		const struct btf_param *param = &btf_params(func_proto)[arg_no];
		const struct bpf_ctx_arg_aux *info;
		const struct btf_type *t;
		int offset;

		if (args->args[arg_no] != 0)
			continue;

		/* Program is validated already, so there is no need
		 * to check if t is NULL.
		 */
		t = btf_type_skip_modifiers(bpf_dummy_ops_btf, param->type, NULL);
		if (!btf_type_is_ptr(t))
			continue;

		offset = btf_ctx_arg_offset(bpf_dummy_ops_btf, func_proto, arg_no);
		info = find_ctx_arg_info(prog->aux, offset);
		if (info && type_may_be_null(info->reg_type))
			continue;

		return -EINVAL;
	}

	return 0;
}

extern const struct bpf_link_ops bpf_struct_ops_link_lops;

int bpf_struct_ops_test_run(struct bpf_prog *prog, const union bpf_attr *kattr,
			    union bpf_attr __user *uattr)
{
	const struct bpf_struct_ops *st_ops = &bpf_bpf_dummy_ops;
	const struct btf_type *func_proto;
	struct bpf_dummy_ops_test_args *args;
	struct bpf_tramp_links *tlinks = NULL;
	struct bpf_tramp_link *link = NULL;
	void *image = NULL;
	unsigned int op_idx;
	u32 image_off = 0;
	int prog_ret;
	s32 type_id;
	int err;

	type_id = btf_find_by_name_kind(bpf_dummy_ops_btf,
					bpf_bpf_dummy_ops.name,
					BTF_KIND_STRUCT);
	if (type_id < 0)
		return -EINVAL;
	if (prog->aux->attach_btf_id != type_id)
		return -EOPNOTSUPP;

	func_proto = prog->aux->attach_func_proto;
	args = dummy_ops_init_args(kattr, btf_type_vlen(func_proto));
	if (IS_ERR(args))
		return PTR_ERR(args);

	err = check_test_run_args(prog, args);
	if (err)
		goto out;

	tlinks = kcalloc(BPF_TRAMP_MAX, sizeof(*tlinks), GFP_KERNEL);
	if (!tlinks) {
		err = -ENOMEM;
		goto out;
	}

	link = kzalloc(sizeof(*link), GFP_USER);
	if (!link) {
		err = -ENOMEM;
		goto out;
	}
	/* prog doesn't take the ownership of the reference from caller */
	bpf_prog_inc(prog);
	bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_struct_ops_link_lops, prog,
		      prog->expected_attach_type);

	op_idx = prog->expected_attach_type;
	err = bpf_struct_ops_prepare_trampoline(tlinks, link,
						&st_ops->func_models[op_idx],
						&dummy_ops_test_ret_function,
						&image, &image_off,
						true);
	if (err < 0)
		goto out;

	err = arch_protect_bpf_trampoline(image, PAGE_SIZE);
	if (err)
		goto out;
	prog_ret = dummy_ops_call_op(image, args);

	err = dummy_ops_copy_args(args);
	if (err)
		goto out;
	if (put_user(prog_ret, &uattr->test.retval))
		err = -EFAULT;
out:
	kfree(args);
	bpf_struct_ops_image_free(image);
	if (link)
		bpf_link_put(&link->link);
	kfree(tlinks);
	return err;
}

static int bpf_dummy_init(struct btf *btf)
{
	bpf_dummy_ops_btf = btf;
	return 0;
}

static bool bpf_dummy_ops_is_valid_access(int off, int size,
					  enum bpf_access_type type,
					  const struct bpf_prog *prog,
					  struct bpf_insn_access_aux *info)
{
	return bpf_tracing_btf_ctx_access(off, size, type, prog, info);
}

static int bpf_dummy_ops_check_member(const struct btf_type *t,
				      const struct btf_member *member,
				      const struct bpf_prog *prog)
{
	u32 moff = __btf_member_bit_offset(t, member) / 8;

	switch (moff) {
	case offsetof(struct bpf_dummy_ops, test_sleepable):
		break;
	default:
		if (prog->sleepable)
			return -EINVAL;
	}

	return 0;
}

static int bpf_dummy_ops_btf_struct_access(struct bpf_verifier_log *log,
					   const struct bpf_reg_state *reg,
					   int off, int size)
{
	const struct btf_type *state;
	const struct btf_type *t;
	s32 type_id;

	type_id = btf_find_by_name_kind(reg->btf, "bpf_dummy_ops_state",
					BTF_KIND_STRUCT);
	if (type_id < 0)
		return -EINVAL;

	t = btf_type_by_id(reg->btf, reg->btf_id);
	state = btf_type_by_id(reg->btf, type_id);
	if (t != state) {
		bpf_log(log, "only access to bpf_dummy_ops_state is supported\n");
		return -EACCES;
	}

	if (off + size > sizeof(struct bpf_dummy_ops_state)) {
		bpf_log(log, "write access at off %d with size %d\n", off, size);
		return -EACCES;
	}

	return NOT_INIT;
}

static const struct bpf_verifier_ops bpf_dummy_verifier_ops = {
	.is_valid_access = bpf_dummy_ops_is_valid_access,
	.btf_struct_access = bpf_dummy_ops_btf_struct_access,
};

static int bpf_dummy_init_member(const struct btf_type *t,
				 const struct btf_member *member,
				 void *kdata, const void *udata)
{
	return -EOPNOTSUPP;
}

static int bpf_dummy_reg(void *kdata, struct bpf_link *link)
{
	return -EOPNOTSUPP;
}

static void bpf_dummy_unreg(void *kdata, struct bpf_link *link)
{
}

static int bpf_dummy_ops__test_1(struct bpf_dummy_ops_state *cb__nullable)
{
	return 0;
}

static int bpf_dummy_test_2(struct bpf_dummy_ops_state *cb, int a1, unsigned short a2,
			    char a3, unsigned long a4)
{
	return 0;
}

static int bpf_dummy_test_sleepable(struct bpf_dummy_ops_state *cb)
{
	return 0;
}

static struct bpf_dummy_ops __bpf_bpf_dummy_ops = {
	.test_1 = bpf_dummy_ops__test_1,
	.test_2 = bpf_dummy_test_2,
	.test_sleepable = bpf_dummy_test_sleepable,
};

static struct bpf_struct_ops bpf_bpf_dummy_ops = {
	.verifier_ops = &bpf_dummy_verifier_ops,
	.init = bpf_dummy_init,
	.check_member = bpf_dummy_ops_check_member,
	.init_member = bpf_dummy_init_member,
	.reg = bpf_dummy_reg,
	.unreg = bpf_dummy_unreg,
	.name = "bpf_dummy_ops",
	.cfi_stubs = &__bpf_bpf_dummy_ops,
	.owner = THIS_MODULE,
};

static int __init bpf_dummy_struct_ops_init(void)
{
	return register_bpf_struct_ops(&bpf_bpf_dummy_ops, bpf_dummy_ops);
}
late_initcall(bpf_dummy_struct_ops_init);