[PATCH bpf-next] selftests/bpf: veristat: Minimize map size during verification

[Emil Tsalapatis <emil@etsalapatis.com>]

The veristat tool verifies that BPF objects along with their
maps pass verification for a given kernel version. To do so,
veristat loads the objects and maps into the kernel in order
to pass them through the verifier.

Currently, veristat sizes the maps according to the max_entries
field provided by the program author. Depending on the map type
this field may be irrelevant to the verification process. However,
loading a large map can fail because of -ENOMEM errors.

This is a problem when the map is supposed to run on large machines,
but veristat tests it machines with significantly less RAM (e.g.,
CI). In that case veristat fails even if the program verifies.

Expand veristat to resize maps whose max_entries are not relevant
to verification. Set the max_entries value as low as possible to
avoid -ENOMEM errors.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
---
 tools/testing/selftests/bpf/veristat.c | 46 ++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/tools/testing/selftests/bpf/veristat.c b/tools/testing/selftests/bpf/veristat.c
index a7db6f04f7e1..8d374e140653 100644
--- a/tools/testing/selftests/bpf/veristat.c
+++ b/tools/testing/selftests/bpf/veristat.c
@@ -37,6 +37,10 @@
 #define min(a, b) ((a) < (b) ? (a) : (b))
 #endif
 
+#ifndef div_round_up
+#define div_round_up(a, b) (((a) + (b) - 1) / (b))
+#endif
+
 enum stat_id {
 	VERDICT,
 	DURATION,
@@ -1238,6 +1242,17 @@ static void mask_unrelated_struct_ops_progs(struct bpf_object *obj,
 	}
 }
 
+/* size of global arena data in pages (minimum 1) */
+static size_t arena_global_pages(struct bpf_map *map)
+{
+	size_t min_bytes;
+
+	if (!bpf_map__initial_value(map, &min_bytes))
+		return 1;
+
+	return div_round_up(min_bytes, sysconf(_SC_PAGESIZE)) ?: 1;
+}
+
 static void fixup_obj_maps(struct bpf_object *obj)
 {
 	struct bpf_map *map;
@@ -1248,6 +1263,37 @@ static void fixup_obj_maps(struct bpf_object *obj)
 
 		/* fix up map size, if necessary */
 		switch (bpf_map__type(map)) {
+		/*
+		 * if the verifier doesn't use max_entries
+		 * then set to 1 to avoid -ENOMEM
+		 */
+		case BPF_MAP_TYPE_HASH:
+		case BPF_MAP_TYPE_PERCPU_HASH:
+		case BPF_MAP_TYPE_LRU_HASH:
+		case BPF_MAP_TYPE_LRU_PERCPU_HASH:
+		case BPF_MAP_TYPE_HASH_OF_MAPS:
+		case BPF_MAP_TYPE_RHASH:
+		case BPF_MAP_TYPE_SOCKHASH:
+		case BPF_MAP_TYPE_DEVMAP_HASH:
+		case BPF_MAP_TYPE_LPM_TRIE:
+		case BPF_MAP_TYPE_QUEUE:
+		case BPF_MAP_TYPE_STACK:
+		case BPF_MAP_TYPE_BLOOM_FILTER:
+		case BPF_MAP_TYPE_STACK_TRACE:
+			bpf_map__set_max_entries(map, 1);
+			break;
+
+		/* arenas must be big enough to fit all globals */
+		case BPF_MAP_TYPE_ARENA:
+			bpf_map__set_max_entries(map, arena_global_pages(map));
+			break;
+
+		/* ringbufs must be page-aligned */
+		case BPF_MAP_TYPE_RINGBUF:
+		case BPF_MAP_TYPE_USER_RINGBUF:
+			bpf_map__set_max_entries(map, sysconf(_SC_PAGESIZE));
+			break;
+
 		case BPF_MAP_TYPE_SK_STORAGE:
 		case BPF_MAP_TYPE_TASK_STORAGE:
 		case BPF_MAP_TYPE_INODE_STORAGE:
-- 
2.54.0