Merge branch 'bpf: add bpf_for_each_map_elem() helper'

Yonghong Song says:

====================

This patch set introduced bpf_for_each_map_elem() helper.
The helper permits bpf program iterates through all elements
for a particular map.

The work originally inspired by an internal discussion where
firewall rules are kept in a map and bpf prog wants to
check packet 5 tuples against all rules in the map.
A bounded loop can be used but it has a few drawbacks.
As the loop iteration goes up, verification time goes up too.
For really large maps, verification may fail.
A helper which abstracts out the loop itself will not have
verification time issue.

A recent discussion in [1] involves to iterate all hash map
elements in bpf program. Currently iterating all hashmap elements
in bpf program is not easy if key space is really big.
Having a helper to abstract out the loop itself is even more
meaningful.

The proposed helper signature looks like:
  long bpf_for_each_map_elem(map, callback_fn, callback_ctx, flags)
where callback_fn is a static function and callback_ctx is
a piece of data allocated on the caller stack which can be
accessed by the callback_fn. The callback_fn signature might be
different for different maps. For example, for hash/array maps,
the signature is
  long callback_fn(map, key, val, callback_ctx)

In the rest of series, Patches 1/2/3/4 did some refactoring. Patch 5
implemented core kernel support for the helper. Patches 6 and 7
added hashmap and arraymap support. Patches 8/9 added libbpf
support. Patch 10 added bpftool support. Patches 11 and 12 added
selftests for hashmap and arraymap.

[1]: https://lore.kernel.org/bpf/20210122205415.113822-1-xiyou.wangcong@gmail.com/

Changelogs:
  v4 -> v5:
    - rebase on top of bpf-next.
  v3 -> v4:
    - better refactoring of check_func_call(), calculate subprogno outside
      of __check_func_call() helper. (Andrii)
    - better documentation (like the list of supported maps and their
      callback signatures) in uapi header. (Andrii)
    - implement and use ASSERT_LT in selftests. (Andrii)
    - a few other minor changes.
  v2 -> v3:
    - add comments in retrieve_ptr_limit(), which is in sanitize_ptr_alu(),
      to clarify the code is not executed for PTR_TO_MAP_KEY handling,
      but code is manually tested. (Alexei)
    - require BTF for callback function. (Alexei)
    - simplify hashmap/arraymap callback return handling as return value
      [0, 1] has been enforced by the verifier. (Alexei)
    - also mark global subprog (if used in ld_imm64) as RELO_SUBPROG_ADDR. (Andrii)
    - handle the condition to mark RELO_SUBPROG_ADDR properly. (Andrii)
    - make bpftool subprog insn offset dumping consist with pcrel calls. (Andrii)
  v1 -> v2:
    - setup callee frame in check_helper_call() and then proceed to verify
      helper return value as normal (Alexei)
    - use meta data to keep track of map/func pointer to avoid hard coding
      the register number (Alexei)
    - verify callback_fn return value range [0, 1]. (Alexei)
    - add migrate_{disable, enable} to ensure percpu value is the one
      bpf program expects to see. (Alexei)
    - change bpf_for_each_map_elem() return value to the number of iterated
      elements. (Andrii)
    - Change libbpf pseudo_func relo name to RELO_SUBPROG_ADDR and use
      more rigid checking for the relocation. (Andrii)
    - Better format to print out subprog address with bpftool. (Andrii)
    - Use bpf_prog_test_run to trigger bpf run, instead of bpf_iter. (Andrii)
    - Other misc changes.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 79c893310492..b89af20cfa19 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -393,6 +393,15 @@ enum bpf_link_type {
  *                   is struct/union.
  */
 #define BPF_PSEUDO_BTF_ID	3
+/* insn[0].src_reg:  BPF_PSEUDO_FUNC
+ * insn[0].imm:      insn offset to the func
+ * insn[1].imm:      0
+ * insn[0].off:      0
+ * insn[1].off:      0
+ * ldimm64 rewrite:  address of the function
+ * verifier type:    PTR_TO_FUNC.
+ */
+#define BPF_PSEUDO_FUNC		4
 
 /* when bpf_call->src_reg == BPF_PSEUDO_CALL, bpf_call->imm == pc-relative
  * offset to another bpf function
@@ -3909,6 +3918,34 @@ union bpf_attr {
  *		* **BPF_MTU_CHK_RET_FRAG_NEEDED**
  *		* **BPF_MTU_CHK_RET_SEGS_TOOBIG**
  *
+ * long bpf_for_each_map_elem(struct bpf_map *map, void *callback_fn, void *callback_ctx, u64 flags)
+ *	Description
+ *		For each element in **map**, call **callback_fn** function with
+ *		**map**, **callback_ctx** and other map-specific parameters.
+ *		The **callback_fn** should be a static function and
+ *		the **callback_ctx** should be a pointer to the stack.
+ *		The **flags** is used to control certain aspects of the helper.
+ *		Currently, the **flags** must be 0.
+ *
+ *		The following are a list of supported map types and their
+ *		respective expected callback signatures:
+ *
+ *		BPF_MAP_TYPE_HASH, BPF_MAP_TYPE_PERCPU_HASH,
+ *		BPF_MAP_TYPE_LRU_HASH, BPF_MAP_TYPE_LRU_PERCPU_HASH,
+ *		BPF_MAP_TYPE_ARRAY, BPF_MAP_TYPE_PERCPU_ARRAY
+ *
+ *		long (\*callback_fn)(struct bpf_map \*map, const void \*key, void \*value, void \*ctx);
+ *
+ *		For per_cpu maps, the map_value is the value on the cpu where the
+ *		bpf_prog is running.
+ *
+ *		If **callback_fn** return 0, the helper will continue to the next
+ *		element. If return value is 1, the helper will skip the rest of
+ *		elements and return. Other return values are not used now.
+ *
+ *	Return
+ *		The number of traversed map elements for success, **-EINVAL** for
+ *		invalid **flags**.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -4075,6 +4112,7 @@ union bpf_attr {
 	FN(ima_inode_hash),		\
 	FN(sock_from_file),		\
 	FN(check_mtu),			\
+	FN(for_each_map_elem),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper