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Date: Fri, 27 Dec 2019 06:16:28 +0000
From: Martin Lau <kafai@...com>
To: Yonghong Song <yhs@...com>
CC: "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
David Miller <davem@...emloft.net>,
Kernel Team <Kernel-team@...com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 06/11] bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS
On Mon, Dec 23, 2019 at 11:57:48AM -0800, Yonghong Song 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;
> > +
> > + uvalue = (struct bpf_struct_ops_value *)value;
> > + 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;
> > + mtype = btf_type_by_id(btf_vmlinux, member->type);
> > + ptype = btf_type_resolve_ptr(btf_vmlinux, member->type, NULL);
> > + if (ptype == module_type) {
> > + *(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 (!btf_type_resolve_func_ptr(btf_vmlinux, member->type,
> > + NULL)) {
> > + u32 msize;
> > +
> > + 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_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;
> > + }
>
> Should we check whether user indeed provided `module` member or
> not before declaring success?
hmm.... By 'module', you meant the "if (ptype == module_type)" logic
at the beginning? Yes, it should check user passed 0 also.
will fix.
> > +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);
> > + /* Each trampoline costs < 64 bytes. Ensure one page
> > + * is enough for max number of func ptrs.
> > + */
> > + BUILD_BUG_ON(PAGE_SIZE / 64 < BPF_STRUCT_OPS_MAX_NR_MEMBERS);
>
> This maybe true for x86 now, but it may not hold up for future other
> architectures. Not sure whether we should get the value for arch call
> backs, or we just bail out during map update if we ever grow exceeds
> one page.
I will reuse the existing WARN_ON_ONCE() check in arch_prepare_bpf_trampoline().
Need to parameterize the end-of-image (i.e. the current PAGE_SIZE / 2 assumption).
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