Re: [PATCH bpf-next 3/3] selftests/bpf: add tests for bpf_dynptr_copy

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

On 21/02/2025 00:52, Andrii Nakryiko wrote:
> On Tue, Feb 18, 2025 at 11:01 AM Mykyta Yatsenko
> <mykyta.yatsenko5@gmail.com> wrote:
>> From: Mykyta Yatsenko <yatsenko@meta.com>
>>
>> Add XDP setup type for dynptr tests, enabling testing for
>> non-contiguous buffer.
>> Add 2 tests:
>>   - test_dynptr_copy - verify correctness for the fast (contiguous
>>   buffer) code path.
>>   - test_dynptr_copy_xdp - verifies code paths that handle
>>   non-contiguous buffer.
>>
>> Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
>> ---
>>   tools/testing/selftests/bpf/bpf_kfuncs.h      |  8 ++
>>   .../testing/selftests/bpf/prog_tests/dynptr.c | 25 ++++++
>>   .../selftests/bpf/progs/dynptr_success.c      | 77 +++++++++++++++++++
>>   3 files changed, 110 insertions(+)
>>
>> diff --git a/tools/testing/selftests/bpf/bpf_kfuncs.h b/tools/testing/selftests/bpf/bpf_kfuncs.h
>> index 8215c9b3115e..e9c193036c82 100644
>> --- a/tools/testing/selftests/bpf/bpf_kfuncs.h
>> +++ b/tools/testing/selftests/bpf/bpf_kfuncs.h
>> @@ -43,6 +43,14 @@ extern bool bpf_dynptr_is_rdonly(const struct bpf_dynptr *ptr) __ksym __weak;
>>   extern __u32 bpf_dynptr_size(const struct bpf_dynptr *ptr) __ksym __weak;
>>   extern int bpf_dynptr_clone(const struct bpf_dynptr *ptr, struct bpf_dynptr *clone__init) __ksym __weak;
>>
>> +/* Description
>> + *  Copy data from one dynptr to another
>> + * Returns
>> + *  Error code
>> + */
>> +extern int bpf_dynptr_copy(struct bpf_dynptr *dst, __u32 dst_off,
>> +                          struct bpf_dynptr *src, __u32 src_off, __u32 size) __ksym __weak;
>> +
> Do we *need* this? Doesn't all this come from vmlinux.h nowadays?
>
>>   /* Description
>>    *  Modify the address of a AF_UNIX sockaddr.
>>    * Returns
>> diff --git a/tools/testing/selftests/bpf/prog_tests/dynptr.c b/tools/testing/selftests/bpf/prog_tests/dynptr.c
>> index b614a5272dfd..247618958155 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/dynptr.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/dynptr.c
>> @@ -10,6 +10,7 @@ enum test_setup_type {
>>          SETUP_SYSCALL_SLEEP,
>>          SETUP_SKB_PROG,
>>          SETUP_SKB_PROG_TP,
>> +       SETUP_XDP_PROG,
>>   };
>>
>>   static struct {
>> @@ -18,6 +19,8 @@ static struct {
>>   } success_tests[] = {
>>          {"test_read_write", SETUP_SYSCALL_SLEEP},
>>          {"test_dynptr_data", SETUP_SYSCALL_SLEEP},
>> +       {"test_dynptr_copy", SETUP_SYSCALL_SLEEP},
>> +       {"test_dynptr_copy_xdp", SETUP_XDP_PROG},
>>          {"test_ringbuf", SETUP_SYSCALL_SLEEP},
>>          {"test_skb_readonly", SETUP_SKB_PROG},
>>          {"test_dynptr_skb_data", SETUP_SKB_PROG},
>> @@ -120,6 +123,28 @@ static void verify_success(const char *prog_name, enum test_setup_type setup_typ
>>
>>                  break;
>>          }
>> +       case SETUP_XDP_PROG:
>> +       {
>> +               char data[5000];
>> +               int err, prog_fd;
>> +
> no empty line here, opts is a variable
>
>> +               LIBBPF_OPTS(bpf_test_run_opts, opts,
>> +                           .data_in = &data,
>> +                           .data_size_in = sizeof(data),
>> +                           .repeat = 1,
>> +               );
>> +
>> +               prog_fd = bpf_program__fd(prog);
>> +               if (!ASSERT_GE(prog_fd, 0, "prog_fd"))
>> +                       goto cleanup;
>
> we shouldn't check this, if program loaded successfully this will
> always be true (and yeah, I know that existing code does that, we
> should remove or at least not duplicate this)
>
>> +
>> +               err = bpf_prog_test_run_opts(prog_fd, &opts);
>> +
>> +               if (!ASSERT_OK(err, "test_run"))
>> +                       goto cleanup;
>> +
>> +               break;
>> +       }
>>          }
>>
>>          ASSERT_EQ(skel->bss->err, 0, "err");
>> diff --git a/tools/testing/selftests/bpf/progs/dynptr_success.c b/tools/testing/selftests/bpf/progs/dynptr_success.c
>> index bfcc85686cf0..8a6b35418e39 100644
>> --- a/tools/testing/selftests/bpf/progs/dynptr_success.c
>> +++ b/tools/testing/selftests/bpf/progs/dynptr_success.c
>> @@ -567,3 +567,80 @@ int BPF_PROG(test_dynptr_skb_tp_btf, void *skb, void *location)
>>
>>          return 1;
>>   }
>> +
>> +SEC("?tp/syscalls/sys_enter_nanosleep")
>> +int test_dynptr_copy(void *ctx)
>> +{
>> +       char *data = "hello there, world!!";
>> +       char buf[32] = {'\0'};
>> +       __u32 sz = strlen(data);
> this is fragile, this is not guaranteed to work (only if compiler just
> substituted a constant value). maybe just use data[] = "hello
> there..." and use sizeof(data) then?
>
>> +       struct bpf_dynptr src, dst;
>> +
>> +       bpf_ringbuf_reserve_dynptr(&ringbuf, sz, 0, &src);
>> +       bpf_ringbuf_reserve_dynptr(&ringbuf, sz, 0, &dst);
>> +
>> +       err = bpf_dynptr_write(&src, 0, data, sz, 0);
>> +       err = err ?: bpf_dynptr_copy(&dst, 0, &src, 0, sz);
>> +       err = err ?: bpf_dynptr_read(buf, sz, &dst, 0, 0);
>> +       err = err ?: __builtin_memcmp(data, buf, sz);
>> +
>> +       err = err ?: bpf_dynptr_copy(&dst, 3, &src, 5, sz - 5);
>> +       err = err ?: bpf_dynptr_read(buf, sz - 5, &dst, 3, 0);
>> +       err = err ?: __builtin_memcmp(data + 5, buf, sz - 5);
>> +
>> +       bpf_ringbuf_discard_dynptr(&src, 0);
>> +       bpf_ringbuf_discard_dynptr(&dst, 0);
>> +       return 0;
>> +}
>> +
>> +SEC("xdp")
>> +int test_dynptr_copy_xdp(struct xdp_md *xdp)
>> +{
>> +       struct bpf_dynptr ptr_buf, ptr_xdp;
>> +       char *data = "qwertyuiopasdfghjkl;";
>> +       char buf[32] = {'\0'};
>> +       __u32 len = strlen(data);
> ditto
>
>> +       int i, chunks = 200;
>> +
>> +       bpf_dynptr_from_xdp(xdp, 0, &ptr_xdp);
>> +       bpf_ringbuf_reserve_dynptr(&ringbuf, len * chunks, 0, &ptr_buf);
>> +
>> +       bpf_for(i, 0, chunks) {
>> +               err =  err ?: bpf_dynptr_write(&ptr_buf, i * len, data, len, 0);
>> +       }
>> +
>> +       err = err ?: bpf_dynptr_copy(&ptr_xdp, 0, &ptr_buf, 0, len * chunks);
>> +
>> +       bpf_for(i, 0, chunks) {
>> +               memset(buf, 0, sizeof(buf));
> __builtin_memset(), memset() works only because compiler optimizes it
> to built-in, but let's not rely on that
>
>> +               err = err ?: bpf_dynptr_read(&buf, len, &ptr_xdp, i * len, 0);
>> +               err = err ?: memcmp(data, buf, len);
> __builtin_memcmp() and all the other cases below, please
>
>> +       }
>> +
>> +       memset(buf, 0, sizeof(buf));
>> +       bpf_for(i, 0, chunks) {
>> +               err = err ?: bpf_dynptr_write(&ptr_buf, i * len, buf, len, 0);
>> +       }
>> +
>> +       err = err ?: bpf_dynptr_copy(&ptr_buf, 0, &ptr_xdp, 0, len * chunks);
>> +
>> +       bpf_for(i, 0, chunks) {
>> +               memset(buf, 0, sizeof(buf));
>> +               err = err ?: bpf_dynptr_read(&buf, len, &ptr_buf, i * len, 0);
>> +               err = err ?: memcmp(data, buf, len);
>> +       }
>> +
>> +       bpf_ringbuf_discard_dynptr(&ptr_buf, 0);
>> +
>> +       err = err ?: bpf_dynptr_copy(&ptr_xdp, 2, &ptr_xdp, len, len * (chunks - 1));
>> +
>> +       bpf_for(i, 0, chunks - 1) {
>> +               memset(buf, 0, sizeof(buf));
>> +               err = err ?: bpf_dynptr_read(&buf, len, &ptr_xdp, 2 + i * len, 0);
>> +               err = err ?: memcmp(data, buf, len);
>> +       }
>> +
>> +       err = err ?: (bpf_dynptr_copy(&ptr_xdp, 2000, &ptr_xdp, 0, len * chunks) == -E2BIG ? 0 : 1);
> overdoing it a bit with the whole `err ?: ` pattern, IMO
>
>
> BTW, more questions to networking folks (maybe Martin knows). Is there
> a way to setup SKB or XDP packet with a non-linear region for testing?
The setup I made in dynptr.c for XDP makes non-linear region.
It looks like maximum linear mem size is 4k, so when going above that,
it creates multiple frags in xdp_buff:

```

char data[5000];
...
.data_in = &data,

```

I verified that in this test xdp_buff is non-linear, and all non-fast 
code paths of
the bpf_dynptr_copy are tested.

>
>> +
>> +       return XDP_DROP;
>> +}
>> --
>> 2.48.1
>>
Thanks for findings, fixing them in v2.