netdev - Re: [PATCH bpf-next v4 1/2] bpf, xdp: make bpf_redirect

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Date:   Sat, 27 Feb 2021 10:04:40 +0100
From:   Björn Töpel <bjorn.topel@...el.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     maciej.fijalkowski@...el.com, hawk@...nel.org, toke@...hat.com,
        magnus.karlsson@...el.com, john.fastabend@...il.com,
        kuba@...nel.org, davem@...emloft.net,
        Björn Töpel <bjorn.topel@...il.com>,
        bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...nel.org
Subject: Re: [PATCH bpf-next v4 1/2] bpf, xdp: make bpf_redirect_map() a map
 operation



On 2021-02-26 22:48, Daniel Borkmann wrote:
> On 2/26/21 12:23 PM, Björn Töpel wrote:
>> From: Björn Töpel <bjorn.topel@...el.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@...el.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


Björn


>> +                continue;
>>               }
>>               goto patch_call_imm;