Re: [RFC v3 03/22] bpf,landlock: Add a new arraymap type to deal with (Landlock) handles

[Alexei Starovoitov]

On Wed, Sep 14, 2016 at 09:23:56AM +0200, Mickaël Salaün wrote:
> This new arraymap looks like a set and brings new properties:
> * strong typing of entries: the eBPF functions get the array type of
>   elements instead of CONST_PTR_TO_MAP (e.g.
>   CONST_PTR_TO_LANDLOCK_HANDLE_FS);
> * force sequential filling (i.e. replace or append-only update), which
>   allow quick browsing of all entries.
> 
> This strong typing is useful to statically check if the content of a map
> can be passed to an eBPF function. For example, Landlock use it to store
> and manage kernel objects (e.g. struct file) instead of dealing with
> userland raw data. This improve efficiency and ensure that an eBPF
> program can only call functions with the right high-level arguments.
> 
> The enum bpf_map_handle_type list low-level types (e.g.
> BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD) which are identified when
> updating a map entry (handle). This handle types are used to infer a
> high-level arraymap type which are listed in enum bpf_map_array_type
> (e.g. BPF_MAP_ARRAY_TYPE_LANDLOCK_FS).
> 
> For now, this new arraymap is only used by Landlock LSM (cf. next
> commits) but it could be useful for other needs.
> 
> Changes since v2:
> * add a RLIMIT_NOFILE-based limit to the maximum number of arraymap
>   handle entries (suggested by Andy Lutomirski)
> * remove useless checks
> 
> Changes since v1:
> * arraymap of handles replace custom checker groups
> * simpler userland API
> 
> Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Link: https://lkml.kernel.org/r/CALCETrWwTiz3kZTkEgOW24-DvhQq6LftwEXh77FD2G5o71yD7g@xxxxxxxxxxxxxx
> ---
>  include/linux/bpf.h      |  14 ++++
>  include/uapi/linux/bpf.h |  18 +++++
>  kernel/bpf/arraymap.c    | 203 +++++++++++++++++++++++++++++++++++++++++++++++
>  kernel/bpf/verifier.c    |  12 ++-
>  4 files changed, 246 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index fa9a988400d9..eae4ce4542c1 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -13,6 +13,10 @@
>  #include <linux/percpu.h>
>  #include <linux/err.h>
>  
> +#ifdef CONFIG_SECURITY_LANDLOCK
> +#include <linux/fs.h> /* struct file */
> +#endif /* CONFIG_SECURITY_LANDLOCK */
> +
>  struct perf_event;
>  struct bpf_map;
>  
> @@ -38,6 +42,7 @@ struct bpf_map_ops {
>  struct bpf_map {
>  	atomic_t refcnt;
>  	enum bpf_map_type map_type;
> +	enum bpf_map_array_type map_array_type;
>  	u32 key_size;
>  	u32 value_size;
>  	u32 max_entries;
> @@ -187,6 +192,9 @@ struct bpf_array {
>  	 */
>  	enum bpf_prog_type owner_prog_type;
>  	bool owner_jited;
> +#ifdef CONFIG_SECURITY_LANDLOCK
> +	u32 n_entries;	/* number of entries in a handle array */
> +#endif /* CONFIG_SECURITY_LANDLOCK */
>  	union {
>  		char value[0] __aligned(8);
>  		void *ptrs[0] __aligned(8);
> @@ -194,6 +202,12 @@ struct bpf_array {
>  	};
>  };
>  
> +#ifdef CONFIG_SECURITY_LANDLOCK
> +struct map_landlock_handle {
> +	u32 type; /* enum bpf_map_handle_type */
> +};
> +#endif /* CONFIG_SECURITY_LANDLOCK */
> +
>  #define MAX_TAIL_CALL_CNT 32
>  
>  struct bpf_event_entry {
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 7cd36166f9b7..b68de57f7ab8 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -87,6 +87,15 @@ enum bpf_map_type {
>  	BPF_MAP_TYPE_PERCPU_ARRAY,
>  	BPF_MAP_TYPE_STACK_TRACE,P_TYPE_CGROUP_ARRAY
>  	BPF_MAP_TYPE_CGROUP_ARRAY,
> +	BPF_MAP_TYPE_LANDLOCK_ARRAY,
> +};
> +
> +enum bpf_map_array_type {
> +	BPF_MAP_ARRAY_TYPE_UNSPEC,
> +};
> +
> +enum bpf_map_handle_type {
> +	BPF_MAP_HANDLE_TYPE_UNSPEC,
>  };

missing something. why it has to be special to have it's own
fd array implementation?
Please take a look how BPF_MAP_TYPE_PERF_EVENT_ARRAY, 
BPF_MAP_TYPE_CGROUP_ARRAY and BPF_MAP_TYPE_PROG_ARRAY are done.
The all store objects into array map that user space passes via FD.
I think the same model should apply here.