Re: [PATCH v1 bpf-next 4/4] selftests/bpf: Add tests exercising aggregate type BTF field search

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On 10/23/23 3:00 PM, Dave Marchevsky wrote:
The newly-added test file attempts to kptr_xchg a prog_test_ref_kfunc
kptr into a kptr field in a variety of nested aggregate types. If the
verifier recognizes that there's a kptr field where we're trying to
kptr_xchg, then the aggregate type digging logic works as expected.

Some of the refactoring changes in this series are tested as well.
Specifically:
   * BTF_FIELDS_MAX is now higher and represents the max size of the
     growable array. Confirm that btf_parse_fields fails for a type which
     contains too many fields.
   * If we've already seen BTF_FIELDS_MAX fields, we should continue
     looking for fields and fail if we find another one, otherwise the
     search should succeed and return BTF_FIELDS_MAX btf_field_infos.
     Confirm that this edge case works as expected.

Signed-off-by: Dave Marchevsky <davemarchevsky@xxxxxx>
---
  .../selftests/bpf/prog_tests/array_kptr.c     |  12 ++
  .../testing/selftests/bpf/progs/array_kptr.c  | 179 ++++++++++++++++++
  2 files changed, 191 insertions(+)
  create mode 100644 tools/testing/selftests/bpf/prog_tests/array_kptr.c
  create mode 100644 tools/testing/selftests/bpf/progs/array_kptr.c

diff --git a/tools/testing/selftests/bpf/prog_tests/array_kptr.c b/tools/testing/selftests/bpf/prog_tests/array_kptr.c
new file mode 100644
index 000000000000..9d088520bdfe
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/array_kptr.c
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
+
+#include <test_progs.h>
+
+#include "array_kptr.skel.h"
+
+void test_array_kptr(void)
+{
+	if (env.has_testmod)
+		RUN_TESTS(array_kptr);
+}
diff --git a/tools/testing/selftests/bpf/progs/array_kptr.c b/tools/testing/selftests/bpf/progs/array_kptr.c
new file mode 100644
index 000000000000..f34872e74024
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/array_kptr.c
@@ -0,0 +1,179 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+#include "../bpf_testmod/bpf_testmod_kfunc.h"
+#include "bpf_misc.h"
+
+struct val {
+	int d;
+	struct prog_test_ref_kfunc __kptr *ref_ptr;
+};
+
+struct val2 {
+	char c;
+	struct val v;
+};
+
+struct val_holder {
+	int e;
+	struct val2 first[2];
+	int f;
+	struct val second[2];
+};
+
+struct array_map {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, int);
+	__type(value, struct val);
+	__uint(max_entries, 10);
+} array_map SEC(".maps");
+
+struct array_map2 {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, int);
+	__type(value, struct val2);
+	__uint(max_entries, 10);
+} array_map2 SEC(".maps");
+
+__hidden struct val array[25];
+__hidden struct val double_array[5][5];
+__hidden struct val_holder double_holder_array[2][2];
+
+/* Some tests need their own section to force separate bss arraymap,
+ * otherwise above arrays wouldn't have btf_field_info either
+ */
+#define private(name) SEC(".bss." #name) __hidden __attribute__((aligned(8)))
+private(A) struct val array_too_big[300];
+
+private(B) struct val exactly_max_fields[256];
+private(B) int ints[50];
+
+SEC("tc")
+__success __retval(0)
+int test_arraymap(void *ctx)
+{
+	struct prog_test_ref_kfunc *p;
+	unsigned long dummy = 0;
+	struct val *v;
+	int idx = 0;
+
+	v = bpf_map_lookup_elem(&array_map, &idx);
+	if (!v)
+		return 1;
+
+	p = bpf_kfunc_call_test_acquire(&dummy);
+	if (!p)
+		return 2;
+
+	p = bpf_kptr_xchg(&v->ref_ptr, p);
+	if (p) {
+		bpf_kfunc_call_test_release(p);
+		return 3;
+	}
+
+	return 0;
+}
+
...
+
+SEC("tc")
+__failure __msg("map '.bss.A' has no valid kptr")

The .bss.A might have valid kptr.
To reflect realiaty, maybe error message can be
'has too many special fields'?

+int test_array_fail__too_big(void *ctx)
+{
+	/* array_too_big's btf_record parsing will fail due to the
+	 * number of btf_field_infos being > BTF_FIELDS_MAX
+	 */
+	return test_array_xchg(&array_too_big[50]);
+}
+
+char _license[] SEC("license") = "GPL";




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