linux-kernel - Re: [PATCH 1/3] bpf: verifier: Accept dynptr mem as mem in helpers

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Date:   Mon, 1 May 2023 18:12:33 -0700
From:   Daniel Rosenberg <drosen@...gle.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Joanne Koong <joannelkoong@...il.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Mykola Lysenko <mykolal@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH 1/3] bpf: verifier: Accept dynptr mem as mem in helpers

On Thu, Apr 6, 2023 at 3:13 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> +1
> All of the DYNPTR_TYPE_FLAG_MASK flags cannot appear in type == 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.