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Date:   Tue, 5 Feb 2019 16:39:04 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     Andrii Nakryiko <andriin@...com>, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>, kernel-team@...com
Subject: Re: [PATCH bpf-next] tools/bpf: fix a selftest test_btf failure

On Tue, Feb 5, 2019 at 2:30 PM Yonghong Song <yhs@...com> wrote:
>
> Commit 9c651127445c ("selftests/btf: add initial BTF dedup tests")
> added dedup tests in test_btf.c.
> It broke the raw test:
>  BTF raw test[71] (func proto (Bad arg name_off)):
>     btf_raw_create:2905:FAIL Error getting string #65535, strs_cnt:1

Argh.. Thanks for fixing this!

>
> The test itself encodes invalid func_proto parameter name
> offset 0xffffFFFF as a negative test for the kernel.
> The above commit changed the meaning of that offset and
> resulted in a user space error.
>   #define NAME_NTH(N) (0xffff0000 | N)
>   #define IS_NAME_NTH(X) ((X & 0xffff0000) == 0xffff0000)
>   #define GET_NAME_NTH_IDX(X) (X & 0x0000ffff)
>
> Currently, the kernel permits maximum name offset 0xffff.
> Set the test name off as 0x0fffFFFF to trigger the kernel
> verification failure.
>
> Cc: Andrii Nakryiko <andriin@...com>
> Fixes: 9c651127445c ("selftests/btf: add initial BTF dedup tests")
> Signed-off-by: Yonghong Song <yhs@...com>
> ---
>  tools/testing/selftests/bpf/test_btf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/test_btf.c b/tools/testing/selftests/bpf/test_btf.c
> index 30c3edde7e07..447acc34db94 100644
> --- a/tools/testing/selftests/bpf/test_btf.c
> +++ b/tools/testing/selftests/bpf/test_btf.c
> @@ -1978,7 +1978,7 @@ static struct btf_raw_test raw_tests[] = {
>                 /* void (*)(int a, unsigned int <bad_name_off>) */
>                 BTF_FUNC_PROTO_ENC(0, 2),                       /* [3] */
>                         BTF_FUNC_PROTO_ARG_ENC(NAME_TBD, 1),
> -                       BTF_FUNC_PROTO_ARG_ENC(0xffffffff, 2),
> +                       BTF_FUNC_PROTO_ARG_ENC(0x0fffffff, 2),
>                 BTF_END_RAW,
>         },
>         .str_sec = "\0a",
> --
> 2.17.1
>

Acked-by: Andrii Nakryiko <andriin@...com>

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