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>

7 files changed, 405 insertions, 9 deletions

diff --git a/tools/bpf/bpftool/xlated_dumper.c b/tools/bpf/bpftool/xlated_dumper.c
index 8608cd68cdd0..6fc3e6f7f40c 100644
--- a/tools/bpf/bpftool/xlated_dumper.c
+++ b/tools/bpf/bpftool/xlated_dumper.c
@@ -196,6 +196,9 @@ static const char *print_imm(void *private_data,
 	else if (insn->src_reg == BPF_PSEUDO_MAP_VALUE)
 		snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
 			 "map[id:%u][0]+%u", insn->imm, (insn + 1)->imm);
+	else if (insn->src_reg == BPF_PSEUDO_FUNC)
+		snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
+			 "subprog[%+d]", insn->imm);
 	else
 		snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
 			 "0x%llx", (unsigned long long)full_imm);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 79c893310492..b89af20cfa19 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/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
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index d43cc3f29dae..62d9ed56b081 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -188,6 +188,7 @@ enum reloc_type {
 	RELO_CALL,
 	RELO_DATA,
 	RELO_EXTERN,
+	RELO_SUBPROG_ADDR,
 };
 
 struct reloc_desc {
@@ -574,6 +575,16 @@ static bool insn_is_subprog_call(const struct bpf_insn *insn)
 	       insn->off == 0;
 }
 
+static bool is_ldimm64(struct bpf_insn *insn)
+{
+	return insn->code == (BPF_LD | BPF_IMM | BPF_DW);
+}
+
+static bool insn_is_pseudo_func(struct bpf_insn *insn)
+{
+	return is_ldimm64(insn) && insn->src_reg == BPF_PSEUDO_FUNC;
+}
+
 static int
 bpf_object__init_prog(struct bpf_object *obj, struct bpf_program *prog,
 		      const char *name, size_t sec_idx, const char *sec_name,
@@ -2974,6 +2985,23 @@ static bool sym_is_extern(const GElf_Sym *sym)
 	       GELF_ST_TYPE(sym->st_info) == STT_NOTYPE;
 }
 
+static bool sym_is_subprog(const GElf_Sym *sym, int text_shndx)
+{
+	int bind = GELF_ST_BIND(sym->st_info);
+	int type = GELF_ST_TYPE(sym->st_info);
+
+	/* in .text section */
+	if (sym->st_shndx != text_shndx)
+		return false;
+
+	/* local function */
+	if (bind == STB_LOCAL && type == STT_SECTION)
+		return true;
+
+	/* global function */
+	return bind == STB_GLOBAL && type == STT_FUNC;
+}
+
 static int find_extern_btf_id(const struct btf *btf, const char *ext_name)
 {
 	const struct btf_type *t;
@@ -3395,7 +3423,7 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
 		return 0;
 	}
 
-	if (insn->code != (BPF_LD | BPF_IMM | BPF_DW)) {
+	if (!is_ldimm64(insn)) {
 		pr_warn("prog '%s': invalid relo against '%s' for insns[%d].code 0x%x\n",
 			prog->name, sym_name, insn_idx, insn->code);
 		return -LIBBPF_ERRNO__RELOC;
@@ -3430,6 +3458,23 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
 		return -LIBBPF_ERRNO__RELOC;
 	}
 
+	/* loading subprog addresses */
+	if (sym_is_subprog(sym, obj->efile.text_shndx)) {
+		/* global_func: sym->st_value = offset in the section, insn->imm = 0.
+		 * local_func: sym->st_value = 0, insn->imm = offset in the section.
+		 */
+		if ((sym->st_value % BPF_INSN_SZ) || (insn->imm % BPF_INSN_SZ)) {
+			pr_warn("prog '%s': bad subprog addr relo against '%s' at offset %zu+%d\n",
+				prog->name, sym_name, (size_t)sym->st_value, insn->imm);
+			return -LIBBPF_ERRNO__RELOC;
+		}
+
+		reloc_desc->type = RELO_SUBPROG_ADDR;
+		reloc_desc->insn_idx = insn_idx;
+		reloc_desc->sym_off = sym->st_value;
+		return 0;
+	}
+
 	type = bpf_object__section_to_libbpf_map_type(obj, shdr_idx);
 	sym_sec_name = elf_sec_name(obj, elf_sec_by_idx(obj, shdr_idx));
 
@@ -5566,11 +5611,6 @@ static void bpf_core_poison_insn(struct bpf_program *prog, int relo_idx,
 	insn->imm = 195896080; /* => 0xbad2310 => "bad relo" */
 }
 
-static bool is_ldimm64(struct bpf_insn *insn)
-{
-	return insn->code == (BPF_LD | BPF_IMM | BPF_DW);
-}
-
 static int insn_bpf_size_to_bytes(struct bpf_insn *insn)
 {
 	switch (BPF_SIZE(insn->code)) {
@@ -6172,6 +6212,10 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
 			}
 			relo->processed = true;
 			break;
+		case RELO_SUBPROG_ADDR:
+			insn[0].src_reg = BPF_PSEUDO_FUNC;
+			/* will be handled as a follow up pass */
+			break;
 		case RELO_CALL:
 			/* will be handled as a follow up pass */
 			break;
@@ -6358,11 +6402,11 @@ bpf_object__reloc_code(struct bpf_object *obj, struct bpf_program *main_prog,
 
 	for (insn_idx = 0; insn_idx < prog->sec_insn_cnt; insn_idx++) {
 		insn = &main_prog->insns[prog->sub_insn_off + insn_idx];
-		if (!insn_is_subprog_call(insn))
+		if (!insn_is_subprog_call(insn) && !insn_is_pseudo_func(insn))
 			continue;
 
 		relo = find_prog_insn_relo(prog, insn_idx);
-		if (relo && relo->type != RELO_CALL) {
+		if (relo && relo->type != RELO_CALL && relo->type != RELO_SUBPROG_ADDR) {
 			pr_warn("prog '%s': unexpected relo for insn #%zu, type %d\n",
 				prog->name, insn_idx, relo->type);
 			return -LIBBPF_ERRNO__RELOC;
@@ -6374,8 +6418,22 @@ bpf_object__reloc_code(struct bpf_object *obj, struct bpf_program *main_prog,
 			 * call always has imm = -1, but for static functions
 			 * relocation is against STT_SECTION and insn->imm
 			 * points to a start of a static function
+			 *
+			 * for subprog addr relocation, the relo->sym_off + insn->imm is
+			 * the byte offset in the corresponding section.
 			 */
-			sub_insn_idx = relo->sym_off / BPF_INSN_SZ + insn->imm + 1;
+			if (relo->type == RELO_CALL)
+				sub_insn_idx = relo->sym_off / BPF_INSN_SZ + insn->imm + 1;
+			else
+				sub_insn_idx = (relo->sym_off + insn->imm) / BPF_INSN_SZ;
+		} else if (insn_is_pseudo_func(insn)) {
+			/*
+			 * RELO_SUBPROG_ADDR relo is always emitted even if both
+			 * functions are in the same section, so it shouldn't reach here.
+			 */
+			pr_warn("prog '%s': missing subprog addr relo for insn #%zu\n",
+				prog->name, insn_idx);
+			return -LIBBPF_ERRNO__RELOC;
 		} else {
 			/* if subprogram call is to a static function within
 			 * the same ELF section, there won't be any relocation
diff --git a/tools/testing/selftests/bpf/prog_tests/for_each.c b/tools/testing/selftests/bpf/prog_tests/for_each.c
new file mode 100644
index 000000000000..68eb12a287d4
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/for_each.c
@@ -0,0 +1,130 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include <test_progs.h>
+#include <network_helpers.h>
+#include "for_each_hash_map_elem.skel.h"
+#include "for_each_array_map_elem.skel.h"
+
+static unsigned int duration;
+
+static void test_hash_map(void)
+{
+	int i, err, hashmap_fd, max_entries, percpu_map_fd;
+	struct for_each_hash_map_elem *skel;
+	__u64 *percpu_valbuf = NULL;
+	__u32 key, num_cpus, retval;
+	__u64 val;
+
+	skel = for_each_hash_map_elem__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "for_each_hash_map_elem__open_and_load"))
+		return;
+
+	hashmap_fd = bpf_map__fd(skel->maps.hashmap);
+	max_entries = bpf_map__max_entries(skel->maps.hashmap);
+	for (i = 0; i < max_entries; i++) {
+		key = i;
+		val = i + 1;
+		err = bpf_map_update_elem(hashmap_fd, &key, &val, BPF_ANY);
+		if (!ASSERT_OK(err, "map_update"))
+			goto out;
+	}
+
+	num_cpus = bpf_num_possible_cpus();
+	percpu_map_fd = bpf_map__fd(skel->maps.percpu_map);
+	percpu_valbuf = malloc(sizeof(__u64) * num_cpus);
+	if (!ASSERT_OK_PTR(percpu_valbuf, "percpu_valbuf"))
+		goto out;
+
+	key = 1;
+	for (i = 0; i < num_cpus; i++)
+		percpu_valbuf[i] = i + 1;
+	err = bpf_map_update_elem(percpu_map_fd, &key, percpu_valbuf, BPF_ANY);
+	if (!ASSERT_OK(err, "percpu_map_update"))
+		goto out;
+
+	err = bpf_prog_test_run(bpf_program__fd(skel->progs.test_pkt_access),
+				1, &pkt_v4, sizeof(pkt_v4), NULL, NULL,
+				&retval, &duration);
+	if (CHECK(err || retval, "ipv4", "err %d errno %d retval %d\n",
+		  err, errno, retval))
+		goto out;
+
+	ASSERT_EQ(skel->bss->hashmap_output, 4, "hashmap_output");
+	ASSERT_EQ(skel->bss->hashmap_elems, max_entries, "hashmap_elems");
+
+	key = 1;
+	err = bpf_map_lookup_elem(hashmap_fd, &key, &val);
+	ASSERT_ERR(err, "hashmap_lookup");
+
+	ASSERT_EQ(skel->bss->percpu_called, 1, "percpu_called");
+	ASSERT_LT(skel->bss->cpu, num_cpus, "num_cpus");
+	ASSERT_EQ(skel->bss->percpu_map_elems, 1, "percpu_map_elems");
+	ASSERT_EQ(skel->bss->percpu_key, 1, "percpu_key");
+	ASSERT_EQ(skel->bss->percpu_val, skel->bss->cpu + 1, "percpu_val");
+	ASSERT_EQ(skel->bss->percpu_output, 100, "percpu_output");
+out:
+	free(percpu_valbuf);
+	for_each_hash_map_elem__destroy(skel);
+}
+
+static void test_array_map(void)
+{
+	__u32 key, num_cpus, max_entries, retval;
+	int i, arraymap_fd, percpu_map_fd, err;
+	struct for_each_array_map_elem *skel;
+	__u64 *percpu_valbuf = NULL;
+	__u64 val, expected_total;
+
+	skel = for_each_array_map_elem__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "for_each_array_map_elem__open_and_load"))
+		return;
+
+	arraymap_fd = bpf_map__fd(skel->maps.arraymap);
+	expected_total = 0;
+	max_entries = bpf_map__max_entries(skel->maps.arraymap);
+	for (i = 0; i < max_entries; i++) {
+		key = i;
+		val = i + 1;
+		/* skip the last iteration for expected total */
+		if (i != max_entries - 1)
+			expected_total += val;
+		err = bpf_map_update_elem(arraymap_fd, &key, &val, BPF_ANY);
+		if (!ASSERT_OK(err, "map_update"))
+			goto out;
+	}
+
+	num_cpus = bpf_num_possible_cpus();
+	percpu_map_fd = bpf_map__fd(skel->maps.percpu_map);
+	percpu_valbuf = malloc(sizeof(__u64) * num_cpus);
+	if (!ASSERT_OK_PTR(percpu_valbuf, "percpu_valbuf"))
+		goto out;
+
+	key = 0;
+	for (i = 0; i < num_cpus; i++)
+		percpu_valbuf[i] = i + 1;
+	err = bpf_map_update_elem(percpu_map_fd, &key, percpu_valbuf, BPF_ANY);
+	if (!ASSERT_OK(err, "percpu_map_update"))
+		goto out;
+
+	err = bpf_prog_test_run(bpf_program__fd(skel->progs.test_pkt_access),
+				1, &pkt_v4, sizeof(pkt_v4), NULL, NULL,
+				&retval, &duration);
+	if (CHECK(err || retval, "ipv4", "err %d errno %d retval %d\n",
+		  err, errno, retval))
+		goto out;
+
+	ASSERT_EQ(skel->bss->arraymap_output, expected_total, "array_output");
+	ASSERT_EQ(skel->bss->cpu + 1, skel->bss->percpu_val, "percpu_val");
+
+out:
+	free(percpu_valbuf);
+	for_each_array_map_elem__destroy(skel);
+}
+
+void test_for_each(void)
+{
+	if (test__start_subtest("hash_map"))
+		test_hash_map();
+	if (test__start_subtest("array_map"))
+		test_array_map();
+}
diff --git a/tools/testing/selftests/bpf/progs/for_each_array_map_elem.c b/tools/testing/selftests/bpf/progs/for_each_array_map_elem.c
new file mode 100644
index 000000000000..75e8e1069fe7
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/for_each_array_map_elem.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 3);
+	__type(key, __u32);
+	__type(value, __u64);
+} arraymap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u64);
+} percpu_map SEC(".maps");
+
+struct callback_ctx {
+	int output;
+};
+
+static __u64
+check_array_elem(struct bpf_map *map, __u32 *key, __u64 *val,
+		 struct callback_ctx *data)
+{
+	data->output += *val;
+	if (*key == 1)
+		return 1; /* stop the iteration */
+	return 0;
+}
+
+__u32 cpu = 0;
+__u64 percpu_val = 0;
+
+static __u64
+check_percpu_elem(struct bpf_map *map, __u32 *key, __u64 *val,
+		  struct callback_ctx *data)
+{
+	cpu = bpf_get_smp_processor_id();
+	percpu_val = *val;
+	return 0;
+}
+
+u32 arraymap_output = 0;
+
+SEC("classifier")
+int test_pkt_access(struct __sk_buff *skb)
+{
+	struct callback_ctx data;
+
+	data.output = 0;
+	bpf_for_each_map_elem(&arraymap, check_array_elem, &data, 0);
+	arraymap_output = data.output;
+
+	bpf_for_each_map_elem(&percpu_map, check_percpu_elem, (void *)0, 0);
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/for_each_hash_map_elem.c b/tools/testing/selftests/bpf/progs/for_each_hash_map_elem.c
new file mode 100644
index 000000000000..913dd91aafff
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/for_each_hash_map_elem.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 3);
+	__type(key, __u32);
+	__type(value, __u64);
+} hashmap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERCPU_HASH);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u64);
+} percpu_map SEC(".maps");
+
+struct callback_ctx {
+	struct __sk_buff *ctx;
+	int input;
+	int output;
+};
+
+static __u64
+check_hash_elem(struct bpf_map *map, __u32 *key, __u64 *val,
+		struct callback_ctx *data)
+{
+	struct __sk_buff *skb = data->ctx;
+	__u32 k;
+	__u64 v;
+
+	if (skb) {
+		k = *key;
+		v = *val;
+		if (skb->len == 10000 && k == 10 && v == 10)
+			data->output = 3; /* impossible path */
+		else
+			data->output = 4;
+	} else {
+		data->output = data->input;
+		bpf_map_delete_elem(map, key);
+	}
+
+	return 0;
+}
+
+__u32 cpu = 0;
+__u32 percpu_called = 0;
+__u32 percpu_key = 0;
+__u64 percpu_val = 0;
+int percpu_output = 0;
+
+static __u64
+check_percpu_elem(struct bpf_map *map, __u32 *key, __u64 *val,
+		  struct callback_ctx *unused)
+{
+	struct callback_ctx data;
+
+	percpu_called++;
+	cpu = bpf_get_smp_processor_id();
+	percpu_key = *key;
+	percpu_val = *val;
+
+	data.ctx = 0;
+	data.input = 100;
+	data.output = 0;
+	bpf_for_each_map_elem(&hashmap, check_hash_elem, &data, 0);
+	percpu_output = data.output;
+
+	return 0;
+}
+
+int hashmap_output = 0;
+int hashmap_elems = 0;
+int percpu_map_elems = 0;
+
+SEC("classifier")
+int test_pkt_access(struct __sk_buff *skb)
+{
+	struct callback_ctx data;
+
+	data.ctx = skb;
+	data.input = 10;
+	data.output = 0;
+	hashmap_elems = bpf_for_each_map_elem(&hashmap, check_hash_elem, &data, 0);
+	hashmap_output = data.output;
+
+	percpu_map_elems = bpf_for_each_map_elem(&percpu_map, check_percpu_elem,
+						 (void *)0, 0);
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/test_progs.h b/tools/testing/selftests/bpf/test_progs.h
index f7c2fd89d01a..e87c8546230e 100644
--- a/tools/testing/selftests/bpf/test_progs.h
+++ b/tools/testing/selftests/bpf/test_progs.h
@@ -152,6 +152,17 @@ extern int test__join_cgroup(const char *path);
 	___ok;								\
 })
 
+#define ASSERT_LT(actual, expected, name) ({				\
+	static int duration = 0;					\
+	typeof(actual) ___act = (actual);				\
+	typeof(expected) ___exp = (expected);				\
+	bool ___ok = ___act < ___exp;					\
+	CHECK(!___ok, (name),						\
+	      "unexpected %s: actual %lld >= expected %lld\n",		\
+	      (name), (long long)(___act), (long long)(___exp));	\
+	___ok;								\
+})
+
 #define ASSERT_STREQ(actual, expected, name) ({				\
 	static int duration = 0;					\
 	const char *___act = actual;					\