Re: [PATCH v4 bpf-next 1/2] bpf: Allow ringbuf memory to be used as map key

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On Thu, Sep 22, 2022 at 11:06 PM Dave Marchevsky <davemarchevsky@xxxxxx> wrote:
>
> This patch adds support for the following pattern:
>
>   struct some_data *data = bpf_ringbuf_reserve(&ringbuf, sizeof(struct some_data, 0));
>   if (!data)
>     return;
>   bpf_map_lookup_elem(&another_map, &data->some_field);
>   bpf_ringbuf_submit(data);
>
> Currently the verifier does not consider bpf_ringbuf_reserve's
> PTR_TO_MEM | MEM_ALLOC ret type a valid key input to bpf_map_lookup_elem.
> Since PTR_TO_MEM is by definition a valid region of memory, it is safe
> to use it as a key for lookups.
>
> Signed-off-by: Dave Marchevsky <davemarchevsky@xxxxxx>
> Acked-by: Yonghong Song <yhs@xxxxxx>
> ---
> v2->v3: lore.kernel.org/bpf/20220914123600.927632-1-davemarchevsky@xxxxxx
>
>   * Add Yonghong ack, rebase
>
> v1->v2: lore.kernel.org/bpf/20220912101106.2765921-1-davemarchevsky@xxxxxx
>
>   * Move test changes into separate patch - patch 2 in this series.
>     (Kumar, Yonghong). That patch's changelog enumerates specific
>     changes from v1
>   * Remove PTR_TO_MEM addition from this patch - patch 1 (Yonghong)
>     * I don't have a usecase for PTR_TO_MEM w/o MEM_ALLOC
>   * Add "if (!data)" error check to example pattern in this patch
>     (Yonghong)
>   * Remove patch 2 from v1's series, which removed map_key_value_types
>     as it was more-or-less duplicate of mem_types
>     * Now that PTR_TO_MEM isn't added here, more differences between
>       map_key_value_types and mem_types, and no usecase for PTR_TO_BUF,
>       so drop for now.
>
>  kernel/bpf/verifier.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 6f6d2d511c06..97351ae3e7a7 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -5641,6 +5641,7 @@ static const struct bpf_reg_types map_key_value_types = {
>                 PTR_TO_PACKET_META,
>                 PTR_TO_MAP_KEY,
>                 PTR_TO_MAP_VALUE,
> +               PTR_TO_MEM | MEM_ALLOC,

are there any differences between mem_types and map_key_value_types?
If not, should we just drop map_key_value_types? mem_types also alloc
any PTR_TO_MEM (not just ringbuf's MEM_ALLOC) and PTR_TO_BUF
(tracepoint context structs, I think?)

>         },
>  };
>
> --
> 2.30.2
>



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