Re: [RFC PATCH 2/4] fpga: Add new properties to support user-key encrypted bitstream loading

[Rob Herring <robh@kernel.org>]

On Thu, May 13, 2021 at 5:55 AM Nava kishore Manne <navam@xilinx.com> wrote:
>
> Hi Rob,
>
>         Please find my response inline.
>
> > -----Original Message-----
> > From: Rob Herring <robh@kernel.org>
> > Sent: Thursday, May 13, 2021 8:01 AM
> > To: Nava kishore Manne <navam@xilinx.com>
> > Cc: mdf@kernel.org; trix@redhat.com; Michal Simek <michals@xilinx.com>;
> > arnd@arndb.de; Rajan Vaja <RAJANV@xilinx.com>;
> > gregkh@linuxfoundation.org; linus.walleij@linaro.org; Amit Sunil Dhamne
> > <amitsuni@xlnx.xilinx.com>; Tejas Patel <tejasp@xlnx.xilinx.com>;
> > zou_wei@huawei.com; Manish Narani <MNARANI@xilinx.com>; Sai Krishna
> > Potthuri <lakshmis@xilinx.com>; Jiaying Liang <jliang@xilinx.com>; linux-
> > fpga@vger.kernel.org; devicetree@vger.kernel.org; linux-
> > kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; git
> > <git@xilinx.com>; chinnikishore369@gmail.com
> > Subject: Re: [RFC PATCH 2/4] fpga: Add new properties to support user-key
> > encrypted bitstream loading
> >
> > On Tue, May 04, 2021 at 03:52:25PM +0530, Nava kishore Manne wrote:
> > > This patch Adds ‘encrypted-key-name’ and
> > > ‘encrypted-user-key-fpga-config’ properties to support user-key
> > > encrypted bitstream loading use case.
> > >
> > > Signed-off-by: Nava kishore Manne <nava.manne@xilinx.com>
> > > ---
> > >  Documentation/devicetree/bindings/fpga/fpga-region.txt | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/fpga/fpga-region.txt
> > > b/Documentation/devicetree/bindings/fpga/fpga-region.txt
> > > index d787d57491a1..957dc6cbcd9e 100644
> > > --- a/Documentation/devicetree/bindings/fpga/fpga-region.txt
> > > +++ b/Documentation/devicetree/bindings/fpga/fpga-region.txt
> > > @@ -177,6 +177,9 @@ Optional properties:
> > >     it indicates that the FPGA has already been programmed with this
> > image.
> > >     If this property is in an overlay targeting a FPGA region, it is a
> > >     request to program the FPGA with that image.
> > > +- encrypted-key-name : should contain the name of an encrypted key file
> > located
> > > +   on the firmware search path. It will be used to decrypt the FPGA
> > image
> > > +   file.
> > >  - fpga-bridges : should contain a list of phandles to FPGA Bridges that must
> > be
> > >     controlled during FPGA programming along with the parent FPGA
> > bridge.
> > >     This property is optional if the FPGA Manager handles the bridges.
> > > @@ -187,6 +190,8 @@ Optional properties:
> > >  - external-fpga-config : boolean, set if the FPGA has already been
> > configured
> > >     prior to OS boot up.
> > >  - encrypted-fpga-config : boolean, set if the bitstream is encrypted
> > > +- encrypted-user-key-fpga-config : boolean, set if the bitstream is
> > encrypted
> > > +   with user key.
> >
> > What's the relationship with encrypted-fpga-config? Both present or
> > mutually exclusive? Couldn't this be implied by encrypted-key-name being
> > present?
> >
>
> In Encryption we have two kinds of use case one is Encrypted Bitstream loading with Device-key and
> Other one is Encrypted Bitstream loading with User-key. encrypted-fpga-config and encrypted-user-key-fpga-config
> are mutually exclusive. To differentiate both the use cases I have added this new flag and Aes Key file(encrypted-key-name)
> is needed only for encrypted-user-key-fpga-config use cases.

If encrypted-key-name is required for a user key, then why do you need
encrypted-user-key-fpga-config also?

IOW, why have 3 properties (that's 9 possible combinations) for 2 modes?

Rob