Re: [PATCH 02/12] fpga: sec-mgr: enable secure updates

From: Moritz Fischer <mdf@kernel.org>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Russ Weight <russell.h.weight@intel.com>,
	Tom Rix <trix@redhat.com>, Moritz Fischer <mdf@kernel.org>,
	linux-fpga@vger.kernel.org, moritzf@google.com
Subject: Re: [PATCH 02/12] fpga: sec-mgr: enable secure updates
Date: Wed, 4 Aug 2021 07:58:34 -0700	[thread overview]
Message-ID: <YQqrGvwkf6bJ/5in@archbook> (raw)
In-Reply-To: <YQpDySXy0ASM5u9y@kroah.com>

On Wed, Aug 04, 2021 at 09:37:45AM +0200, Greg KH wrote:
> On Tue, Aug 03, 2021 at 12:02:24PM -0700, Russ Weight wrote:
> > 
> > 
> > On 8/2/21 10:49 PM, Greg KH wrote:
> > >> If the request_firmware() implementation is not acceptable, then would
> > >> you agree that an IOCTL implementation is our best option?
> > > There is no difference in the end between using an ioctl, or a sysfs
> > > file, to provide the filename of your firmware, don't get hung up on
> > > that.
> > 
> > I meant to suggest that passing file data (not a filename) through an
> > IOCTL might be better for this use case than trying to use request_firmware.
> > We have to, somehow, allow the user to point us to the desired image
> > data (which could be a root-entry-hash, or an FPGA image). We can't
> > really use a fixed filename modified by device version as many of
> > the devices do.
> 
> Ah, yes, a "normal" write command might be best for this as that can be
> properly containerized and controlled.
> 
> > > By providing a "filename", you are going around all of the namespace and
> > > other "container" protection that the kernel provides, and allowing
> > > processes to potentially load files that are normally outside of their
> > > scope to the hardware.  If you are willing to allow that security
> > > "escape", wonderful, but you better document the heck out of it and
> > > explain why this is allowed for your special hardware and use case.
> > >
> > > As you are expecting this to work "in the cloud", I do not think that
> > > the operators of such hardware are really going to be all that happy to
> > > see this type of interface given these reasons.
> > >
> > > What is wrong with the current fpga firmware api that somehow is lacking
> > > for your special hardware, that other devices do not have to worry
> > > about?
> > The existing framework wants to update the live image in the FPGA,
> > whereas for this device, we are passing signed data to BMC firmware
> > which will store it in FLASH to be loaded on a subsequent boot of
> > the card.
> > 
> > The existing framework needs to manage FPGA state, whereas for this
> > device, it is just a transfer of signed data. We also have to handle
> > a total transfer/authentication time of up to 45 minutes, so we are
> > using a kernel worker thread for the update.
> > 
> > Perhaps the name, fpga security manager, is wrong? Maybe something
> > like fpga_sec_image_xfer is better?
> 
> It does not sound like this has anything to do with "security", and
> rather is just a normal firmware upload, so "fpga_image_upload()"
> perhaps?

I had originally suggested 'load' and 'persist' or 'load' and 'update or
something of that sort.

Taking one step back, maybe the case could be made for a generic
'persistent firmware' update framework that addresses use-cases that
require updating firmware that may take extended periods of time.

A similar case that comes to mind would be writing firmware to an
external flash on a Renesas xHCI controller, or updating the BMC
firmware for a plug-in card with BMC.

- Moritz