linux-kernel - Re: [RFC PATCH 0/3]fpga: Add encrypted Bitstream loading support

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Date:   Fri, 24 Nov 2023 16:49:07 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Nava kishore Manne <nava.kishore.manne@....com>, mdf@...nel.org,
        hao.wu@...el.com, yilun.xu@...el.com, trix@...hat.com,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, michal.simek@....com,
        mathieu.poirier@...aro.org, ben.levinsky@....com,
        sai.krishna.potthuri@....com, tanmay.shah@....com,
        dhaval.r.shah@....com, arnd@...db.de, shubhrajyoti.datta@....com,
        linux-fpga@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 0/3]fpga: Add encrypted Bitstream loading support

On 22/11/2023 06:44, Nava kishore Manne wrote:
> For user-key encrypted bitstream loading use case, users can encrypt
> FPGA configuration Images with their own key.While decrypting the
> configuration Image the user needs to provide the same key.To support
> this use case with the existing FPGA manager framework is not possible
> because it doesn’t have a mechanism to get the required inputs from
> the user. So this patch series adds the required changes to the FPGA
> manager framework to support user-key encrypted bitstream image loading

Wasn't the entire point of encrypted FPGA bistreams that the key is
fused into the FPGA and the FPGA does the decrypting? Otherwise it's
like security through obscurity - the only trouble for attacker is to
decode DTB to find the filename of key, so actually not even really
obscure. Then the attacker retrieves the key and bitstream from
filesystem (by taking out the Zynq-based SoM out or booting from own
system or just accessing storage pins directly) and voila: encrypted key
is available.

Best regards,
Krzysztof