On 15/09/2016 01:28, Alexei Starovoitov wrote: > On Thu, Sep 15, 2016 at 01:22:49AM +0200, Mickaël Salaün wrote: >> >> On 14/09/2016 20:51, Alexei Starovoitov wrote: >>> 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 <m...@digikod.net> >>>> Cc: Alexei Starovoitov <a...@kernel.org> >>>> Cc: Andy Lutomirski <l...@amacapital.net> >>>> Cc: Daniel Borkmann <dan...@iogearbox.net> >>>> Cc: David S. Miller <da...@davemloft.net> >>>> Cc: Kees Cook <keesc...@chromium.org> >>>> Link: >>>> https://lkml.kernel.org/r/calcetrwwtiz3kztkegow24-dvhqq6lftwexh77fd2g5o71y...@mail.gmail.com >>>> --- >>>> 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. >> >> The idea is to have multiple way for userland to describe a resource >> (e.g. an open file descriptor, a path or a glob pattern). The kernel >> representation could then be a "struct path *" or dedicated types (e.g. >> custom glob). > > hmm. I think user space api should only deal with FD. Everything > else is user space job to encapsulate/hide.
How would you create a FD referring to a glob, a user or port ranges for example ? > >> Another interesting point (that could replace >> check_map_func_compatibility()) is that BPF_MAP_TYPE_LANDLOCK_ARRAY >> translate to dedicated (abstract) types (instead of CONST_PTR_TO_MAP) >> thanks to bpf_reg_type_from_map(). This is useful to abstract userland >> (map) interface with kernel object(s) dealing with that type. > > I probably missing something. If user space interface is FD, > to the kernel they're different object types. Nothing else. Yes but what if there is more than one way to express a resource (cf. previous comment). A FD can refer to an *existing file* but a glob pattern could match a bunch of files (existing or not). This was a concern for Kees Cook and James Morris [1]. [1] https://lkml.kernel.org/r/cagxu5jk1u12vmk11hd_x_gnz3rk4zgefdthy7dhvm4e4spr...@mail.gmail.com > >> A third point is that BPF_MAP_TYPE_LANDLOCK_ARRAY is a kind of set. It >> is optimized to quickly walk through all the elements in a sequential way. > > why set is any faster to walk vs array? It is an array with only sequential entries (i.e. no hole in the array).
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