I had everything working on Ubuntu 16.04 installed on my Dell until the other day when I messed around with it trying to get a live usb recognized in it. Didn't touch it for several days and when I went back to it last night, wifi was not working. When I say not working, I mean it didn't recognize the wifi connection at all in the Network connection manager installed on the panel in Unity (or Gnome). It's a Broadcom wifi module, so I checked Additional Drivers and the Broadcom software was installed. I next connected my Dell to ethernet, updated the software and reinstalled the Broadcom driver. Still no recognition of wifi at all. I don't recall what made me do it (must have been something I read searching for the problem on the internet), but I restarted the Dell and disabled secure boot. When I did that, wifi came back. I can certainly live without secure boot, but I'd like to know how this causes a problem with Broadcom wifi, and whether there is a solution that would allow me to enable secure boot and have my wifi back.
Jason, your suggestion that the wifi module wasn't signed as part of the original installation is logical, but it turns out that the problem is due to a bug. The bug has already been reported on launchpad (https://bugs.launchpad.net/ubuntu/+source/bcmwl/+bug/1572659). That's actually good news because it has been given priority status and it will likely be fixed soon. Meanwhile, I'll stick with secure boot turned off until the problem is fixed. The other solution is to use an older kernel, as 4.4.0-18 has been reported to work, but I won't bother with that.
It's a bug certainly but it does look related to signing:
Look at comment #13:
Agreed. Meanwhile, on the Ubuntu forums where I posted the problem, I was invited to try a signing key called mokutil (see here (http://ubuntuforums.org/showthread.php?t=2327735&p=13504179#post13504179) and here (http://ubuntuforums.org/showthread.php?t=2304607&page=9)). I am afraid of trying this since it hasn't been tested on my Broadcom (wl) driver, and seeing the way it operates with a blank purple screen upon reboot, it looks like it could potentially affect firmware. Even if it works, I wonder if it wouldn't affect my ability to use an updated kernel that fixes the problem. Since I can disable secure boot for now and have everything working, I'm thinking I should just leave things alone until the Ubuntu devs fix the bug.
I don't think it would bork anything either. It's essentially solving the problem by letting you sign the module so it is accepted by system.map and secure boot. I wasn't aware you could do this but I recognize the openssl command that is used to create crypographic signing keys. They will probably fix it in an update to the kernel (and system.map) so any change yo make here will only affect this kernel and be fixed in the next one. It won't prevent your next kernel from working, that is.
More about mokutil here:
https://sourceware.org/systemtap/wiki/SecureBoot
Thanks for that, Jason. Having read that through, there was enough there to give me concern that I am not inclined to use this mechanism to allow me to secure boot with my wifi working. I'll stick to having secure boot disabled for now and just wait until the Ubuntu and/or kernel devs fix the bug. I'm really don't see the need for secure boot anyway on my Dell laptop; it's just an academic issue to me.
Understandable. Especially when it's something as critical as networking.