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Date: Tue, 7 Jan 2020 18:55:36 +0000
From: Martin Lau <kafai@...com>
To: Daniel Borkmann <daniel@...earbox.net>
CC: "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
Alexei Starovoitov <ast@...nel.org>,
David Miller <davem@...emloft.net>,
Kernel Team <Kernel-team@...com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 06/11] bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS
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,
> > +};
> [...]
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