netdev - Re: [PATCH bpf-next 2/2] tools: bpftool: add "bpftool map freeze" subcommand

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Date:   Wed, 21 Aug 2019 13:40:38 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Quentin Monnet <quentin.monnet@...ronome.com>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        oss-drivers@...ronome.com
Subject: Re: [PATCH bpf-next 2/2] tools: bpftool: add "bpftool map freeze"
 subcommand

On 8/21/19 10:52 AM, Quentin Monnet wrote:
> Add a new subcommand to freeze maps from user space.
> 
> Signed-off-by: Quentin Monnet <quentin.monnet@...ronome.com>
> Reviewed-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> ---
>   .../bpf/bpftool/Documentation/bpftool-map.rst |  9 +++++
>   tools/bpf/bpftool/bash-completion/bpftool     |  4 +--
>   tools/bpf/bpftool/map.c                       | 34 ++++++++++++++++++-
>   3 files changed, 44 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/Documentation/bpftool-map.rst b/tools/bpf/bpftool/Documentation/bpftool-map.rst
> index 61d1d270eb5e..1c0f7146aab0 100644
> --- a/tools/bpf/bpftool/Documentation/bpftool-map.rst
> +++ b/tools/bpf/bpftool/Documentation/bpftool-map.rst
> @@ -36,6 +36,7 @@ MAP COMMANDS
>   |	**bpftool** **map pop**        *MAP*
>   |	**bpftool** **map enqueue**    *MAP* **value** *VALUE*
>   |	**bpftool** **map dequeue**    *MAP*
> +|	**bpftool** **map freeze**     *MAP*
>   |	**bpftool** **map help**
>   |
>   |	*MAP* := { **id** *MAP_ID* | **pinned** *FILE* }
> @@ -127,6 +128,14 @@ DESCRIPTION
>   	**bpftool map dequeue**  *MAP*
>   		  Dequeue and print **value** from the queue.
>   
> +	**bpftool map freeze**  *MAP*
> +		  Freeze the map as read-only from user space. Entries from a
> +		  frozen map can not longer be updated or deleted with the
> +		  **bpf\ ()** system call. This operation is not reversible,
> +		  and the map remains immutable from user space until its
> +		  destruction. However, read and write permissions for BPF
> +		  programs to the map remain unchanged.

That is not correct, programs that are loaded into the system /after/ the map
has been frozen cannot modify values either, thus read-only from both sides.

Thanks,
Daniel