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 10:44:41PM +0100, Daniel Borkmann wrote:
> On 1/7/20 7:55 PM, Martin Lau wrote:
> > On Tue, Jan 07, 2020 at 05:00:37PM +0100, Daniel Borkmann wrote:
> > > On 12/31/19 7:20 AM, Martin KaFai Lau wrote:
> > > [...]
> [...]
> > > > +		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?
> 
> True, given the above udata store, makes sense as-is.
> 
> > > > +		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.
> 
> And we could also move the set_memory_x() to that point once image is written and
> marked read-only; mid term text poke interface to avoid all this.
I will respin.

Thanks for the review!  

> 
> Other than that nothing obvious stands out from reviewing patch 1-8, so no objections
> from my side.
> 
> > > > +	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,
> > > > +};
> > > [...]
>