Merge branch 'bpf-allow-bpf_for_each_map_elem-helper-with-different-input-maps'

Philo Lu says:

====================
bpf: allow bpf_for_each_map_elem() helper with different input maps

Currently, taking different maps within a single bpf_for_each_map_elem
call is not allowed. For example the following codes cannot pass the
verifier (with error "tail_call abusing map_ptr"):
```
static void test_by_pid(int pid)
{
	if (pid <= 100)
		bpf_for_each_map_elem(&map1, map_elem_cb, NULL, 0);
	else
		bpf_for_each_map_elem(&map2, map_elem_cb, NULL, 0);
}
```

This is because during bpf_for_each_map_elem verifying,
bpf_insn_aux_data->map_ptr_state is expected as map_ptr (instead of poison
state), which is then needed by set_map_elem_callback_state. However, as
there are two different map ptr input, map_ptr_state is marked as
BPF_MAP_PTR_POISON, and thus the second map_ptr would be lost.
BPF_MAP_PTR_POISON is also needed by bpf_for_each_map_elem to skip
retpoline optimization in do_misc_fixups(). Therefore, map_ptr_state and
map_ptr are both needed for bpf_for_each_map_elem.

This patchset solves it by transform bpf_insn_aux_data->map_ptr_state as a
new struct, storing poison/unpriv state and map pointer together without
additional memory overhead. Then bpf_for_each_map_elem works well with
different input maps. It also makes map_ptr_state logic clearer.

A test case is added to selftest, which would fail to load without this
patchset.

Changelogs
-> v1:
- PATCH 1/3:
  - make the commit log clearer
  - change poison and unpriv to bool in struct bpf_map_ptr_state, also the
    return value in bpf_map_ptr_poisoned() and bpf_map_ptr_unpriv()
- PATCH 2/3:
  - change the comments in set_map_elem_callback_state()
- PATCH 3/3:
  - remove the "skipping the last element" logic during map updating
  - change if() to ASSERT_OK()

Please review, thanks.
====================

Link: https://lore.kernel.org/r/20240405025536.18113-1-lulie@linux.alibaba.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 62 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/for_each.c b/tools/testing/selftests/bpf/prog_tests/for_each.c
index 8963f8a549f2..09f6487f58b9 100644
--- a/tools/testing/selftests/bpf/prog_tests/for_each.c
+++ b/tools/testing/selftests/bpf/prog_tests/for_each.c
@@ -5,6 +5,7 @@
 #include "for_each_hash_map_elem.skel.h"
 #include "for_each_array_map_elem.skel.h"
 #include "for_each_map_elem_write_key.skel.h"
+#include "for_each_multi_maps.skel.h"
 
 static unsigned int duration;
 
@@ -143,6 +144,65 @@ static void test_write_map_key(void)
 		for_each_map_elem_write_key__destroy(skel);
 }
 
+static void test_multi_maps(void)
+{
+	struct for_each_multi_maps *skel;
+	__u64 val, array_total, hash_total;
+	__u32 key, max_entries;
+	int i, err;
+
+	LIBBPF_OPTS(bpf_test_run_opts, topts,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.repeat = 1,
+	);
+
+	skel = for_each_multi_maps__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "for_each_multi_maps__open_and_load"))
+		return;
+
+	array_total = 0;
+	max_entries = bpf_map__max_entries(skel->maps.arraymap);
+	for (i = 0; i < max_entries; i++) {
+		key = i;
+		val = i + 1;
+		array_total += val;
+		err = bpf_map__update_elem(skel->maps.arraymap, &key, sizeof(key),
+					   &val, sizeof(val), BPF_ANY);
+		if (!ASSERT_OK(err, "array_map_update"))
+			goto out;
+	}
+
+	hash_total = 0;
+	max_entries = bpf_map__max_entries(skel->maps.hashmap);
+	for (i = 0; i < max_entries; i++) {
+		key = i + 100;
+		val = i + 1;
+		hash_total += val;
+		err = bpf_map__update_elem(skel->maps.hashmap, &key, sizeof(key),
+					   &val, sizeof(val), BPF_ANY);
+		if (!ASSERT_OK(err, "hash_map_update"))
+			goto out;
+	}
+
+	skel->bss->data_output = 0;
+	skel->bss->use_array = 1;
+	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.test_pkt_access), &topts);
+	ASSERT_OK(err, "bpf_prog_test_run_opts");
+	ASSERT_OK(topts.retval, "retval");
+	ASSERT_EQ(skel->bss->data_output, array_total, "array output");
+
+	skel->bss->data_output = 0;
+	skel->bss->use_array = 0;
+	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.test_pkt_access), &topts);
+	ASSERT_OK(err, "bpf_prog_test_run_opts");
+	ASSERT_OK(topts.retval, "retval");
+	ASSERT_EQ(skel->bss->data_output, hash_total, "hash output");
+
+out:
+	for_each_multi_maps__destroy(skel);
+}
+
 void test_for_each(void)
 {
 	if (test__start_subtest("hash_map"))
@@ -151,4 +211,6 @@ void test_for_each(void)
 		test_array_map();
 	if (test__start_subtest("write_map_key"))
 		test_write_map_key();
+	if (test__start_subtest("multi_maps"))
+		test_multi_maps();
 }