Re: [PATCH bpf-next v4 1/2] bpf, xdp: make bpf_redirect_map() a map operation

[Daniel Borkmann <daniel@iogearbox.net>]

On 2/27/21 10:04 AM, Björn Töpel wrote:
> On 2021-02-26 22:48, Daniel Borkmann wrote:
>> On 2/26/21 12:23 PM, Björn Töpel wrote:
>>> From: Björn Töpel <bjorn.topel@intel.com>
>>>
>>> Currently the bpf_redirect_map() implementation dispatches to the
>>> correct map-lookup function via a switch-statement. To avoid the
>>> dispatching, this change adds bpf_redirect_map() as a map
>>> operation. Each map provides its bpf_redirect_map() version, and
>>> correct function is automatically selected by the BPF verifier.
>>>
>>> A nice side-effect of the code movement is that the map lookup
>>> functions are now local to the map implementation files, which removes
>>> one additional function call.
>>>
>>> Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
>>> ---
>>>   include/linux/bpf.h    | 26 ++++++--------------------
>>>   include/linux/filter.h | 27 +++++++++++++++++++++++++++
>>>   include/net/xdp_sock.h | 19 -------------------
>>>   kernel/bpf/cpumap.c    |  8 +++++++-
>>>   kernel/bpf/devmap.c    | 16 ++++++++++++++--
>>>   kernel/bpf/verifier.c  | 11 +++++++++--
>>>   net/core/filter.c      | 39 +--------------------------------------
>>>   net/xdp/xskmap.c       | 18 ++++++++++++++++++
>>>   8 files changed, 82 insertions(+), 82 deletions(-)
>>>
>>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>>> index cccaef1088ea..a44ba904ca37 100644
>>> --- a/include/linux/bpf.h
>>> +++ b/include/linux/bpf.h
>>> @@ -117,6 +117,9 @@ struct bpf_map_ops {
>>>                          void *owner, u32 size);
>>>       struct bpf_local_storage __rcu ** (*map_owner_storage_ptr)(void *owner);
>>> +    /* XDP helpers.*/
>>> +    int (*xdp_redirect_map)(struct bpf_map *map, u32 ifindex, u64 flags);
>>> +
>>>       /* map_meta_equal must be implemented for maps that can be
>>>        * used as an inner map.  It is a runtime check to ensure
>>>        * an inner map can be inserted to an outer map.
>> [...]
>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>>> index 1dda9d81f12c..96705a49225e 100644
>>> --- a/kernel/bpf/verifier.c
>>> +++ b/kernel/bpf/verifier.c
>>> @@ -5409,7 +5409,8 @@ record_func_map(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
>>>           func_id != BPF_FUNC_map_delete_elem &&
>>>           func_id != BPF_FUNC_map_push_elem &&
>>>           func_id != BPF_FUNC_map_pop_elem &&
>>> -        func_id != BPF_FUNC_map_peek_elem)
>>> +        func_id != BPF_FUNC_map_peek_elem &&
>>> +        func_id != BPF_FUNC_redirect_map)
>>>           return 0;
>>>       if (map == NULL) {
>>> @@ -11762,7 +11763,8 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
>>>                insn->imm == BPF_FUNC_map_delete_elem ||
>>>                insn->imm == BPF_FUNC_map_push_elem   ||
>>>                insn->imm == BPF_FUNC_map_pop_elem    ||
>>> -             insn->imm == BPF_FUNC_map_peek_elem)) {
>>> +             insn->imm == BPF_FUNC_map_peek_elem   ||
>>> +             insn->imm == BPF_FUNC_redirect_map)) {
>>>               aux = &env->insn_aux_data[i + delta];
>>>               if (bpf_map_ptr_poisoned(aux))
>>>                   goto patch_call_imm;
>>> @@ -11804,6 +11806,8 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
>>>                        (int (*)(struct bpf_map *map, void *value))NULL));
>>>               BUILD_BUG_ON(!__same_type(ops->map_peek_elem,
>>>                        (int (*)(struct bpf_map *map, void *value))NULL));
>>> +            BUILD_BUG_ON(!__same_type(ops->xdp_redirect_map,
>>> +                     (int (*)(struct bpf_map *map, u32 ifindex, u64 flags))NULL));
>>>   patch_map_ops_generic:
>>>               switch (insn->imm) {
>>>               case BPF_FUNC_map_lookup_elem:
>>> @@ -11830,6 +11834,9 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
>>>                   insn->imm = BPF_CAST_CALL(ops->map_peek_elem) -
>>>                           __bpf_call_base;
>>>                   continue;
>>> +            case BPF_FUNC_redirect_map:
>>> +                insn->imm = BPF_CAST_CALL(ops->xdp_redirect_map) - __bpf_call_base;
>>
>> Small nit: I would name the generic callback ops->map_redirect so that this is in line with
>> the general naming convention for the map ops. Otherwise this looks much better, thx!
>>
> 
> I'll respin! Thanks for the input!
> 
> I'll ignore the BPF_CAST_CALL W=1 warnings ([-Wcast-function-type]), or
> do you have any thoughts on that? I don't think it's a good idea to
> silence that warning for the whole verifier.c

Makes sense, yes, given they are neither new nor critical for the existing
ones either.

Thanks,
Daniel