Re: [PATCH ipsec-next v3 5/9] libbpf: selftests: Add verifier tests for CO-RE bitfield writes

Andrii Nakryiko
2023-12-01T23:52:57Z

On Fri, Dec 1, 2023 at 12:24 PM Daniel Xu <dxu@dxuuu.xyz> wrote:
>
> Add some tests that exercise BPF_CORE_WRITE_BITFIELD() macro. Since some
> non-trivial bit fiddling is going on, make sure various edge cases (such
> as adjacent bitfields and bitfields at the edge of structs) are
> exercised.
>
> Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
> ---
> .../selftests/bpf/prog_tests/verifier.c | 2 +
> .../bpf/progs/verifier_bitfield_write.c | 100 ++++++++++++++++++
> 2 files changed, 102 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/progs/verifier_bitfield_write.c
>

LGTM, but I'm not sure why we need all those __failure_unpriv, see
below. Regardless:

Acked-by: Andrii Nakryiko <andrii@kernel.org>

> diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
> index 5cfa7a6316b6..67b4948865a3 100644
> --- a/tools/testing/selftests/bpf/prog_tests/verifier.c
> +++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
> @@ -6,6 +6,7 @@
> #include "verifier_and.skel.h"
> #include "verifier_array_access.skel.h"
> #include "verifier_basic_stack.skel.h"
> +#include "verifier_bitfield_write.skel.h"
> #include "verifier_bounds.skel.h"
> #include "verifier_bounds_deduction.skel.h"
> #include "verifier_bounds_deduction_non_const.skel.h"
> @@ -115,6 +116,7 @@ static void run_tests_aux(const char *skel_name,
>
> void test_verifier_and(void) { RUN(verifier_and); }
> void test_verifier_basic_stack(void) { RUN(verifier_basic_stack); }
> +void test_verifier_bitfield_write(void) { RUN(verifier_bitfield_write); }
> void test_verifier_bounds(void) { RUN(verifier_bounds); }
> void test_verifier_bounds_deduction(void) { RUN(verifier_bounds_deduction); }
> void test_verifier_bounds_deduction_non_const(void) { RUN(verifier_bounds_deduction_non_const); }
> diff --git a/tools/testing/selftests/bpf/progs/verifier_bitfield_write.c b/tools/testing/selftests/bpf/progs/verifier_bitfield_write.c
> new file mode 100644
> index 000000000000..8fe355a19ba6
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/verifier_bitfield_write.c
> @@ -0,0 +1,100 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/bpf.h>
> +#include <stdint.h>
> +
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_core_read.h>
> +
> +#include "bpf_misc.h"
> +
> +struct core_reloc_bitfields {
> + /* unsigned bitfields */
> + uint8_t ub1: 1;
> + uint8_t ub2: 2;
> + uint32_t ub7: 7;
> + /* signed bitfields */
> + int8_t sb4: 4;
> + int32_t sb20: 20;
> + /* non-bitfields */
> + uint32_t u32;
> + int32_t s32;
> +} __attribute__((preserve_access_index));
> +
> +SEC("tc")
> +__description("single CO-RE bitfield roundtrip")
> +__btf_path("btf__core_reloc_bitfields.bpf.o")
> +__success __failure_unpriv

do we want __failure_unpriv at all? Is this failure related to
*bitfield* logic at all?

> +__retval(3)
> +int single_field_roundtrip(struct __sk_buff *ctx)
> +{
> + struct core_reloc_bitfields bitfields;
> +
> + __builtin_memset(&bitfields, 0, sizeof(bitfields));
> + BPF_CORE_WRITE_BITFIELD(&bitfields, ub2, 3);
> + return BPF_CORE_READ_BITFIELD(&bitfields, ub2);
> +}
> + …