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References: <20220721153625.1282007-1-benjamin.tissoires@redhat.com> <20220721153625.1282007-6-benjamin.tissoires@redhat.com>
In-Reply-To: <20220721153625.1282007-6-benjamin.tissoires@redhat.com>
From:   Kumar Kartikeya Dwivedi <memxor@gmail.com>
Date:   Thu, 21 Jul 2022 23:05:59 +0200
Message-ID: <CAP01T76_CEGR5Vn+7WCah4oLtv4GUYawhC2X5zUDugG1sTB28Q@mail.gmail.com>
Subject: Re: [PATCH bpf-next v7 05/24] bpf/verifier: allow kfunc to return an
 allocated mem
To:     Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>,
        Jiri Kosina <jikos@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>, Shuah Khan <shuah@kernel.org>,
        Dave Marchevsky <davemarchevsky@fb.com>,
        Joe Stringer <joe@cilium.io>, Jonathan Corbet <corbet@lwn.net>,
        Tero Kristo <tero.kristo@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-input@vger.kernel.org,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org
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On Thu, 21 Jul 2022 at 17:38, Benjamin Tissoires
<benjamin.tissoires@redhat.com> wrote:
>
> For drivers (outside of network), the incoming data is not statically
> defined in a struct. Most of the time the data buffer is kzalloc-ed
> and thus we can not rely on eBPF and BTF to explore the data.
>
> This commit allows to return an arbitrary memory, previously allocated by
> the driver.
> An interesting extra point is that the kfunc can mark the exported
> memory region as read only or read/write.
>
> So, when a kfunc is not returning a pointer to a struct but to a plain
> type, we can consider it is a valid allocated memory assuming that:
> - one of the arguments is either called rdonly_buf_size or
>   rdwr_buf_size
> - and this argument is a const from the caller point of view
>
> We can then use this parameter as the size of the allocated memory.
>
> The memory is either read-only or read-write based on the name
> of the size parameter.
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
>
> ---

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>