Broadcom WLAN kernel module not loaded when secure boot is enabled

[Sebastian]

With a fresh install of Ubuntu 24.04 LTS on an older notebook with a Broadcom BCM4352 WLAN chip and secure boot enabled, I tried to get WiFi running by installing the bcmwl-kernel-source package. Unfortunately, the module does not load:

> sudo modprobe wl
modprobe: ERROR: could not insert 'wl': Key was rejected by service

I was then following the procedure described here, to sign the wl kernel module manually:

https://askubuntu.com/questions/760671/could-not-load-vboxdrv-after-upgrade-to-ubuntu-16-04-and-i-want-to-keep-secur/

This resulted in this warning - but the module wl module did not load either.
>dkms status
broadcom-sta/6.30.223.271, 6.8.0-38-generic, x86_64: installed (WARNING! Diff between built and installed module!)

Can you advise how to get the wl kernel module running? Thank you in advance.

-------------------------------------------------------------------------------------------------

Description: Ubuntu 24.04 LTS
Release: 24.04

bcmwl-kernel-source:
  Installed: 6.30.223.271+bdcom-23ubuntu1
  Candidate: 6.30.223.271+bdcom-23ubuntu1
  Version table:
 *** 6.30.223.271+bdcom-23ubuntu1 500
        500 http://de.archive.ubuntu.com/ubuntu noble/restricted amd64 Packages
        100 /var/lib/dpkg/status

02:00.0 Network controller [0280]: Broadcom Inc. and subsidiaries BCM4352 802.11ac Dual Band Wireless Network Adapter [14e4:43b1] (rev 03)
 Subsystem: Lenovo BCM4352 802.11ac Dual Band Wireless Network Adapter [17aa:0623]
 Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
 Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
 Latency: 0, Cache Line Size: 64 bytes
 Interrupt: pin A routed to IRQ 255
 IOMMU group: 10
 Region 0: Memory at c1200000 (64-bit, non-prefetchable) [size=32K]
 Region 2: Memory at c1000000 (64-bit, non-prefetchable) [size=2M]
 Capabilities: <access denied>
 Kernel modules: bcma, wl

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: bcmwl-kernel-source 6.30.223.271+bdcom-23ubuntu1
ProcVersionSignature: Ubuntu 6.8.0-38.38-generic 6.8.8
Uname: Linux 6.8.0-38-generic x86_64
ApportVersion: 2.28.1-0ubuntu3
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Tue Jul 16 22:38:08 2024
InstallationDate: Installed on 2024-07-14 (2 days ago)
InstallationMedia: Ubuntu 24.04 LTS "Noble Numbat" - Release amd64 (20240424)
ProcEnviron:
 LANG=en_US.UTF-8
 PATH=(custom, no user)
 SHELL=/bin/bash
 TERM=xterm-256color
 XDG_RUNTIME_DIR=<set>
SourcePackage: broadcom-sta
UpgradeStatus: No upgrade log present (probably fresh install)