linux-kernel - Re: [RFC 0/2] of: Add whitelist

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Date:   Tue, 5 Dec 2017 10:55:05 -0600
From:   Alan Tull <atull@...nel.org>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Moritz Fischer <mdf@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-fpga@...r.kernel.org
Subject: Re: [RFC 0/2] of: Add whitelist

On Thu, Nov 30, 2017 at 6:18 AM, Frank Rowand <frowand.list@...il.com> wrote:
> On 11/29/17 08:31, Rob Herring wrote:
>> On Wed, Nov 29, 2017 at 3:20 AM, Frank Rowand <frowand.list@...il.com> wrote:
>>> On 11/27/17 15:58, Alan Tull wrote:
>>>> Here's a proposal for a whitelist to lock down the dynamic device tree.
>>>>
>>>> For an overlay to be accepted, all of its targets are required to be
>>>> on a target node whitelist.
>>>>
>>>> Currently the only way I have to get on the whitelist is calling a
>>>> function to add a node.  That works for fpga regions, but I think
>>>> other uses will need a way of having adding specific nodes from the
>>>> base device tree, such as by adding a property like 'allow-overlay;'
>>>> or 'allow-overlay = "okay";' If that is acceptable, I could use some
>>>> advice on where that particular code should go.
>>>>
>>>> Alan
>>>>
>>>> Alan Tull (2):
>>>>   of: overlay: add whitelist
>>>>   fpga: of region: add of-fpga-region to whitelist
>>>>
>>>>  drivers/fpga/of-fpga-region.c |  9 ++++++
>>>>  drivers/of/overlay.c          | 73 +++++++++++++++++++++++++++++++++++++++++++
>>>>  include/linux/of.h            | 12 +++++++
>>>>  3 files changed, 94 insertions(+)
>>>>
>>>
>>> The plan was to use connectors to restrict where an overlay could be applied.
>>> I would prefer not to have multiple methods for accomplishing the same thing
>>> unless there is a compelling reason to do so.
>>
>> Connector nodes need a mechanism to enable themselves, too. I don't
>> think connector nodes are going to solve every usecase.
>>
>> Rob
>>
>
> The overlay code related to connectors does not exist yet, so my comment
> is going to be theoretical.
>
> I would expect the overlay code to check that the target of the overlay
> fragment is a connector node, so there is no need to explicitly "enable"
> applying an overlay to a connector node.

This will depend on how connectors are implemented.  My proposal in v1
is that device nodes can have a flag bit.  If its not set, then an
overlay that contains fragments that target that node can't be
applied.  There's probably other ways a connector node could be marked
as different from other nodes, but a flag bit seems simple.  The
advantage to this scheme is that it gives me something I can use while
connectors don't exist yet and it will still will be useful later for
the implementation of connectors (giving connector drivers a way of
marking their device nodes as valid targets).

>
> -Frank