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From:   Daniel Rosenberg <drosen@google.com>
Date:   Thu, 6 Apr 2023 15:35:15 -0700
Message-ID: <CA+PiJmQXcgWD3Uu-pRCU6OfkRepeqwr7qi1uO2rfmy0FPm_sOQ@mail.gmail.com>
Subject: Re: [PATCH 1/3] bpf: verifier: Accept dynptr mem as mem in helpers
To:     Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc:     bpf@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        John Fastabend <john.fastabend@gmail.com>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Shuah Khan <shuah@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Joanne Koong <joannelkoong@gmail.com>,
        Mykola Lysenko <mykolal@fb.com>, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, kernel-team@android.com
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On Thu, Apr 6, 2023 at 1:55=E2=80=AFPM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> Something feels off here. Can you paste a bit of verifier log for the
> failure you were getting. And let's have a selftest for this situation
> as well.
>
> ARG_PTR_TO_MEM shouldn't be qualified with the DYNPTR_TYPE flag, it's
> just memory, there is no need to know what type of dynptr it was
> derived from. So if that happens, the problem is somewhere else. Let's
> root cause and fix that. Having a selftest that demonstrates the
> problem will help with that.
>
>
This label is added by dynptr_slice(_rdwr)

if (meta.func_id =3D=3D special_kfunc_list[KF_bpf_dynptr_slice] ||
   meta.func_id =3D=3D special_kfunc_list[KF_bpf_dynptr_slice_rdwr]) {
enum bpf_type_flag type_flag =3D
get_dynptr_type_flag(meta.initialized_dynptr.type);
...
regs[BPF_REG_0].type =3D PTR_TO_MEM | type_flag;

That extra flag was causing the type to be unexpected later on.
I'll add a selftest for this as well.