Re: [PATCH bpf-next v3 06/11] bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS

[Martin Lau <kafai@fb.com>]

On Tue, Jan 07, 2020 at 05:00:37PM +0100, Daniel Borkmann wrote:
> On 12/31/19 7:20 AM, Martin KaFai Lau wrote:
> [...]
> > +static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
> > +					  void *value, u64 flags)
> > +{
> > +	struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;
> > +	const struct bpf_struct_ops *st_ops = st_map->st_ops;
> > +	struct bpf_struct_ops_value *uvalue, *kvalue;
> > +	const struct btf_member *member;
> > +	const struct btf_type *t = st_ops->type;
> > +	void *udata, *kdata;
> > +	int prog_fd, err = 0;
> > +	void *image;
> > +	u32 i;
> > +
> > +	if (flags)
> > +		return -EINVAL;
> > +
> > +	if (*(u32 *)key != 0)
> > +		return -E2BIG;
> > +
> > +	err = check_zero_holes(st_ops->value_type, value);
> > +	if (err)
> > +		return err;
> > +
> > +	uvalue = (struct bpf_struct_ops_value *)value;
> > +	err = check_zero_holes(t, uvalue->data);
> > +	if (err)
> > +		return err;
> > +
> > +	if (uvalue->state || refcount_read(&uvalue->refcnt))
> > +		return -EINVAL;
> > +
> > +	uvalue = (struct bpf_struct_ops_value *)st_map->uvalue;
> > +	kvalue = (struct bpf_struct_ops_value *)&st_map->kvalue;
> > +
> > +	spin_lock(&st_map->lock);
> > +
> > +	if (kvalue->state != BPF_STRUCT_OPS_STATE_INIT) {
> > +		err = -EBUSY;
> > +		goto unlock;
> > +	}
> > +
> > +	memcpy(uvalue, value, map->value_size);
> > +
> > +	udata = &uvalue->data;
> > +	kdata = &kvalue->data;
> > +	image = st_map->image;
> > +
> > +	for_each_member(i, t, member) {
> > +		const struct btf_type *mtype, *ptype;
> > +		struct bpf_prog *prog;
> > +		u32 moff;
> > +
> > +		moff = btf_member_bit_offset(t, member) / 8;
> > +		ptype = btf_type_resolve_ptr(btf_vmlinux, member->type, NULL);
> > +		if (ptype == module_type) {
> > +			if (*(void **)(udata + moff))
> > +				goto reset_unlock;
> > +			*(void **)(kdata + moff) = BPF_MODULE_OWNER;
> > +			continue;
> > +		}
> > +
> > +		err = st_ops->init_member(t, member, kdata, udata);
> > +		if (err < 0)
> > +			goto reset_unlock;
> > +
> > +		/* The ->init_member() has handled this member */
> > +		if (err > 0)
> > +			continue;
> > +
> > +		/* If st_ops->init_member does not handle it,
> > +		 * we will only handle func ptrs and zero-ed members
> > +		 * here.  Reject everything else.
> > +		 */
> > +
> > +		/* All non func ptr member must be 0 */
> > +		if (!ptype || !btf_type_is_func_proto(ptype)) {
> > +			u32 msize;
> > +
> > +			mtype = btf_type_by_id(btf_vmlinux, member->type);
> > +			mtype = btf_resolve_size(btf_vmlinux, mtype, &msize,
> > +						 NULL, NULL);
> > +			if (IS_ERR(mtype)) {
> > +				err = PTR_ERR(mtype);
> > +				goto reset_unlock;
> > +			}
> > +
> > +			if (memchr_inv(udata + moff, 0, msize)) {
> > +				err = -EINVAL;
> > +				goto reset_unlock;
> > +			}
> > +
> > +			continue;
> > +		}
> > +
> > +		prog_fd = (int)(*(unsigned long *)(udata + moff));
> > +		/* Similar check as the attr->attach_prog_fd */
> > +		if (!prog_fd)
> > +			continue;
> > +
> > +		prog = bpf_prog_get(prog_fd);
> > +		if (IS_ERR(prog)) {
> > +			err = PTR_ERR(prog);
> > +			goto reset_unlock;
> > +		}
> > +		st_map->progs[i] = prog;
> > +
> > +		if (prog->type != BPF_PROG_TYPE_STRUCT_OPS ||
> > +		    prog->aux->attach_btf_id != st_ops->type_id ||
> > +		    prog->expected_attach_type != i) {
> > +			err = -EINVAL;
> > +			goto reset_unlock;
> > +		}
> > +
> > +		err = arch_prepare_bpf_trampoline(image,
> > +						  st_map->image + PAGE_SIZE,
> > +						  &st_ops->func_models[i], 0,
> > +						  &prog, 1, NULL, 0, NULL);
> > +		if (err < 0)
> > +			goto reset_unlock;
> > +
> > +		*(void **)(kdata + moff) = image;
> > +		image += err;
> > +
> > +		/* put prog_id to udata */
> > +		*(unsigned long *)(udata + moff) = prog->aux->id;
udata (with all progs' id) will be returned during lookup_elem().

> > +	}
> > +
> > +	refcount_set(&kvalue->refcnt, 1);
> > +	bpf_map_inc(map);
> > +
> > +	err = st_ops->reg(kdata);
> > +	if (!err) {
> > +		/* Pair with smp_load_acquire() during lookup */
> > +		smp_store_release(&kvalue->state, BPF_STRUCT_OPS_STATE_INUSE);
> 
> Is there a reason using READ_ONCE/WRITE_ONCE pair is not enough?
The intention is to ensure lookup_elem() can see all the progs' id once
the state is set to BPF_STRUCT_OPS_STATE_INUSE.

Is READ_ONCE/WRITE_ONCE enough to do this?

> 
> > +		goto unlock;
> > +	}
> > +
> > +	/* Error during st_ops->reg() */
> > +	bpf_map_put(map);
> > +
> > +reset_unlock:
> > +	bpf_struct_ops_map_put_progs(st_map);
> > +	memset(uvalue, 0, map->value_size);
> > +	memset(kvalue, 0, map->value_size);
> > +
> > +unlock:
> > +	spin_unlock(&st_map->lock);
> > +	return err;
> > +}
> [...]
> > +static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
> > +{
> > +	const struct bpf_struct_ops *st_ops;
> > +	size_t map_total_size, st_map_size;
> > +	struct bpf_struct_ops_map *st_map;
> > +	const struct btf_type *t, *vt;
> > +	struct bpf_map_memory mem;
> > +	struct bpf_map *map;
> > +	int err;
> > +
> > +	if (!capable(CAP_SYS_ADMIN))
> > +		return ERR_PTR(-EPERM);
> > +
> > +	st_ops = bpf_struct_ops_find_value(attr->btf_vmlinux_value_type_id);
> > +	if (!st_ops)
> > +		return ERR_PTR(-ENOTSUPP);
> > +
> > +	vt = st_ops->value_type;
> > +	if (attr->value_size != vt->size)
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	t = st_ops->type;
> > +
> > +	st_map_size = sizeof(*st_map) +
> > +		/* kvalue stores the
> > +		 * struct bpf_struct_ops_tcp_congestions_ops
> > +		 */
> > +		(vt->size - sizeof(struct bpf_struct_ops_value));
> > +	map_total_size = st_map_size +
> > +		/* uvalue */
> > +		sizeof(vt->size) +
> > +		/* struct bpf_progs **progs */
> > +		 btf_type_vlen(t) * sizeof(struct bpf_prog *);
> > +	err = bpf_map_charge_init(&mem, map_total_size);
> > +	if (err < 0)
> > +		return ERR_PTR(err);
> > +
> > +	st_map = bpf_map_area_alloc(st_map_size, NUMA_NO_NODE);
> > +	if (!st_map) {
> > +		bpf_map_charge_finish(&mem);
> > +		return ERR_PTR(-ENOMEM);
> > +	}
> > +	st_map->st_ops = st_ops;
> > +	map = &st_map->map;
> > +
> > +	st_map->uvalue = bpf_map_area_alloc(vt->size, NUMA_NO_NODE);
> > +	st_map->progs =
> > +		bpf_map_area_alloc(btf_type_vlen(t) * sizeof(struct bpf_prog *),
> > +				   NUMA_NO_NODE);
> > +	st_map->image = bpf_jit_alloc_exec(PAGE_SIZE);
> > +	if (!st_map->uvalue || !st_map->progs || !st_map->image) {
> > +		bpf_struct_ops_map_free(map);
> > +		bpf_map_charge_finish(&mem);
> > +		return ERR_PTR(-ENOMEM);
> > +	}
> > +
> > +	spin_lock_init(&st_map->lock);
> > +	set_vm_flush_reset_perms(st_map->image);
> > +	set_memory_x((long)st_map->image, 1);
> 
> Shouldn't this be using text poke as well once you write the image later on,
> otherwise we create yet another instance of W+X memory ... :/
Once image is written in update_elem(), it will never be changed.
I can set it to ro after it is written.

> 
> > +	bpf_map_init_from_attr(map, attr);
> > +	bpf_map_charge_move(&map->memory, &mem);
> > +
> > +	return map;
> > +}
> > +
> > +const struct bpf_map_ops bpf_struct_ops_map_ops = {
> > +	.map_alloc_check = bpf_struct_ops_map_alloc_check,
> > +	.map_alloc = bpf_struct_ops_map_alloc,
> > +	.map_free = bpf_struct_ops_map_free,
> > +	.map_get_next_key = bpf_struct_ops_map_get_next_key,
> > +	.map_lookup_elem = bpf_struct_ops_map_lookup_elem,
> > +	.map_delete_elem = bpf_struct_ops_map_delete_elem,
> > +	.map_update_elem = bpf_struct_ops_map_update_elem,
> > +	.map_seq_show_elem = bpf_struct_ops_map_seq_show_elem,
> > +};
> [...]