[PATCH] usb: gadget: sdp: Option to enable SDP read register command

[Loic Poulain]

Hi Marek,

On Mon, 14 Aug 2023 at 01:53, Marek Vasut <marex at denx.de> wrote:
>
> On 8/13/23 10:39, Loic Poulain wrote:
> > The SDP read register command can be used to read any memory
> > mapped address of the device (ddr, registers...). It can then
> > be exploited by an attacker to access sensitive data/values,
> > especially when running SDP from SPL, as SPL runs with highest
> > privileges in ARM secure mode.
> >
> > Without read, SDP still useful to bootstrap and jump on (signed)
> > blob such as u-boot with write and jump commands, but reading
> > is optional in that case (debug purpose).
> >
> > NXP SoCs usually have a dedicated SDP_READ_DISABLE fuse to disable
> > SDP read command in their ROM SDP implementation, so it seems quite
> > reasonable to make it optional from u-boot/spl as well.
>
> If there is a fuse, why not read the fuse and disable READ based on that
> fuse instead ?

Well, fuse is more a way to tune a specific ROM code here, not the software.
It would be more generic to make it a build config like other features, and one
may purposely force SDP READ in SPL, even if disabled at ROM level. That
said we could also introduce a weak board_sdp_read_allowed() function...

Let me know what you prefer.

Regards,
Loic