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

[Yonghong Song <yonghong.song@linux.dev>]

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@fb.com>
> ---
>   .../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";