[PATCH v5 bpf-next 1/4] bpf: Allow ringbuf memory to be used as map key

[Dave Marchevsky <davemarchevsky@fb.com>]

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@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
---
v2->v3: lore.kernel.org/bpf/20220914123600.927632-1-davemarchevsky@fb.com

  * Add Yonghong ack, rebase

v1->v2: lore.kernel.org/bpf/20220912101106.2765921-1-davemarchevsky@fb.com

  * 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,
 	},
 };
 
-- 
2.30.2