Re: [RFC][PATCH 1/2] firmware version management: add firmware_version()

[Jon Smirl]

On 7/9/06, Martin Langer <martin-langer@xxxxxx> wrote:
> On Sat, Jul 08, 2006 at 03:49:57PM +0200, Marcel Holtmann wrote:
> > Hi Arjan,
> >
> > > > It would be good if a driver knows which firmware version will be
> > > > written to the hardware. I'm talking about external firmware files
> > > > claimed by request_firmware().
> > > >
> > > > We know so many different firmware files for bcm43xx and it becomes
> > > > more and more complicated without some firmware version management.
> > > >
> > > > This patch can create the md5sum of a firmware file. Then it looks into
> > > > a table to figure out which version number is assigned to the hashcode.
> > > > That table is placed in the driver code and an example for bcm43xx comes
> > > > in my next mail. Any comments?
> > >
> > > why does this have to happen on the kernel side? Isn't it a lot easier
> > > and better to let the userspace side of things do this work, and even
> > > have a userspace file with the md5->version mapping? Or are there some
> > > practical considerations that make that hard to impossible?
> >
> > I fully agree that we shouldn't put firmware versioning into the kernel
> > drivers. The pattern you give to request_firmware() can be mapped to any
> > file on the file system. And you also have the link to the device object
> > and I prefer you export a sysfs file for the version so that the helper
> > application loading the firmware can pick the right file.
>
> Bcm43xx has no helper application to upload the firmware. This is done
> in the driver. It's RAM based hardware without a Flash-ROM. The driver
> has to upload the firmware in the init phase after each reset.

When your driver does request_firmware() I believe udev is triggering
the /sbin/firmware_helper app.

rules.d/05-udev-early.rules:ACTION=="add", SUBSYSTEM=="firmware",
ENV{FIRMWARE}=="*", RUN="/sbin/firmware_helper", OPTIONS="last_rule"

This app could be made smarter and set a version/checksum into two
more sysfs attributes.

I also though that the firmware loader was going to be modified to
load the firmware via a firmware attribute located in the device node
instead of a global firmware attribute. But it doesn't look like that
change has been made. If the loading were done inside the device node
adding the version/checksum attributes would be more obvious.
/sbin/firmware_helper could set these attributes while loading the
file.

> The driver gets a firmware file from /lib/firmware/ without knowing
> which version this is. It's not possible to say enable this in the
> driver if you find a firmware x and disable that if it's only version
> y. That was my motivation to start thinking about firmware versioning.
>
> But in the meantime I think it's a security issue, too. A driver
> should only accept firmware files with certified checksums. I guess it
> would be really difficult to enter a machine by firmware hijacking. So,
> I'm still in hope that this is only a paranoia on my side. But it's
> worth to think about it.
>
>
> Martin
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--
Jon Smirl
jonsmirl@xxxxxxxxx
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