Re: [PATCH bpf-next v6 3/9] bpf: btf: Introduce helpers for dynamic BTF set registration

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Wed, Sep 29, 2021 at 11:30 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> This adds helpers for registering btf_id_set from modules and the
> check_kfunc_call callback that can be used to look them up.
>
> With in kernel sets, the way this is supposed to work is, in kernel
> callback looks up within the in-kernel kfunc whitelist, and then defers
> to the dynamic BTF set lookup if it doesn't find the BTF id. If there is
> no in-kernel BTF id set, this callback can be used directly.
>
> Also fix includes for btf.h and bpfptr.h so that they can included in
> isolation. This is in preparation for their usage in tcp_bbr, tcp_cubic
> and tcp_dctcp modules in the next patch.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
>  include/linux/bpfptr.h |  1 +
>  include/linux/btf.h    | 31 +++++++++++++++++++++++++
>  kernel/bpf/btf.c       | 51 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 83 insertions(+)
>
> diff --git a/include/linux/bpfptr.h b/include/linux/bpfptr.h
> index 546e27fc6d46..46e1757d06a3 100644
> --- a/include/linux/bpfptr.h
> +++ b/include/linux/bpfptr.h
> @@ -3,6 +3,7 @@
>  #ifndef _LINUX_BPFPTR_H
>  #define _LINUX_BPFPTR_H
>
> +#include <linux/mm.h>
>  #include <linux/sockptr.h>
>
>  typedef sockptr_t bpfptr_t;
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> index 214fde93214b..382c00d5cede 100644
> --- a/include/linux/btf.h
> +++ b/include/linux/btf.h
> @@ -5,6 +5,7 @@
>  #define _LINUX_BTF_H 1
>
>  #include <linux/types.h>
> +#include <linux/bpfptr.h>
>  #include <uapi/linux/btf.h>
>  #include <uapi/linux/bpf.h>
>
> @@ -238,4 +239,34 @@ static inline const char *btf_name_by_offset(const struct btf *btf,
>  }
>  #endif
>
> +struct kfunc_btf_id_set {
> +       struct list_head list;
> +       struct btf_id_set *set;
> +       struct module *owner;
> +};
> +
> +struct kfunc_btf_id_list;
> +
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +void register_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
> +                              struct kfunc_btf_id_set *s);
> +void unregister_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
> +                                struct kfunc_btf_id_set *s);
> +#else
> +static inline void register_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
> +                                            struct kfunc_btf_id_set *s)
> +{
> +}
> +static inline void unregister_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
> +                                              struct kfunc_btf_id_set *s)
> +{
> +}
> +#endif
> +
> +#define DECLARE_CHECK_KFUNC_CALLBACK(type)                                     \
> +       bool __bpf_##type##_check_kfunc_call(u32 kfunc_id, struct module *owner)
> +#define DEFINE_KFUNC_BTF_ID_SET(set, name)                                     \
> +       struct kfunc_btf_id_set name = { LIST_HEAD_INIT(name.list), (set),     \
> +                                        THIS_MODULE }
> +
>  #endif
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index c3d605b22473..5a8806cfecd0 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -6343,3 +6343,54 @@ const struct bpf_func_proto bpf_btf_find_by_name_kind_proto = {
>  };
>
>  BTF_ID_LIST_GLOBAL_SINGLE(btf_task_struct_ids, struct, task_struct)
> +
> +struct kfunc_btf_id_list {
> +       struct list_head list;
> +       struct mutex mutex;
> +};
> +
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +
> +void register_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
> +                              struct kfunc_btf_id_set *s)
> +{
> +       mutex_lock(&l->mutex);
> +       list_add(&s->list, &l->list);
> +       mutex_unlock(&l->mutex);
> +}
> +EXPORT_SYMBOL_GPL(register_kfunc_btf_id_set);
> +
> +void unregister_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
> +                                struct kfunc_btf_id_set *s)
> +{
> +       mutex_lock(&l->mutex);
> +       list_del_init(&s->list);
> +       mutex_unlock(&l->mutex);
> +}
> +EXPORT_SYMBOL_GPL(unregister_kfunc_btf_id_set);
> +
> +#endif
> +
> +#define DEFINE_KFUNC_BTF_ID_LIST(name)                                         \
> +       struct kfunc_btf_id_list name = { LIST_HEAD_INIT(name.list),           \
> +                                         __MUTEX_INITIALIZER(name.mutex) }; \
> +       EXPORT_SYMBOL_GPL(name)
> +

nit: \ alignment seems off

> +#define DEFINE_CHECK_KFUNC_CALLBACK(type, list_name)                           \
> +       bool __bpf_##type##_check_kfunc_call(u32 kfunc_id,                     \
> +                                            struct module *owner)             \

does this have to be a type-specific macro-defined function? It seems
like type is used only for creating a dedicated function with type
embedded in it, but otherwise this helper only needs mutex and the
list, why not code it as a generic function and pass mutex and list
explicitly (or if it is always struct struct kfunc_btf_id_list then
just declare it so)? I think that will be easier to follow.


> +       {                                                                      \
> +               struct kfunc_btf_id_set *s;                                    \
> +               if (!owner || !IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES))      \
> +                       return false;                                          \
> +               mutex_lock(&list_name.mutex);                                  \
> +               list_for_each_entry(s, &list_name.list, list) {                \
> +                       if (s->owner == owner &&                               \
> +                           btf_id_set_contains(s->set, kfunc_id)) {           \
> +                               mutex_unlock(&list_name.mutex);                \
> +                               return true;                                   \
> +                       }                                                      \
> +               }                                                              \
> +               mutex_unlock(&list_name.mutex);                                \
> +               return false;                                                  \
> +       }
> --
> 2.33.0
>