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From:   Daniel Rosenberg <drosen@google.com>
Date:   Mon, 1 May 2023 18:12:33 -0700
Message-ID: <CA+PiJmST4WUH061KaxJ4kRL=fqy3X6+Wgb2E2rrLT5OYjUzxfQ@mail.gmail.com>
Subject: Re: [PATCH 1/3] bpf: verifier: Accept dynptr mem as mem in helpers
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Joanne Koong <joannelkoong@gmail.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@gmail.com>,
        bpf <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>,
        Mykola Lysenko <mykolal@fb.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Android Kernel Team <kernel-team@android.com>
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On Thu, Apr 6, 2023 at 3:13=E2=80=AFPM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> +1
> All of the DYNPTR_TYPE_FLAG_MASK flags cannot appear in type =3D=3D reg->=
type
> here.
> They are either dynamic flags inside bpf_dynptr_kern->size
> or in arg_type.
> Like in bpf_dynptr_from_mem_proto.

Looking at this a bit more, I believe this is to enforce packet
restrictions for DYNPTR_TYPE_SKB and DYNPTR_TYPE_XDP. When a helper
function alters a packet, dynptr slices of it are invalidated. If I
remove that annotation entirely, then the invalid_data_slice family of
tests fail. bpf_dynptr_from_mem_proto is fine since that's just local
dynptrs, which don't have any extra limitations.