When booting with secure boot and kernel lockdown is enabled, OpenCL is unable to use my GPU (GeForce RTX 2080 SUPER). Running "clinfo" shows "Number of platforms 0". If I disable secure boot in my UEFI settings, clinfo shows the details of my GPU as expected.
ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: libnvidia-compute-440 440.100-0ubuntu0.20.04.1
ProcVersionSignature: Ubuntu 5.4.0-40.44-generic 5.4.44
Uname: Linux 5.4.0-40-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.3
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Sat Jul 11 12:08:09 2020
InstallationDate: Installed on 2020-04-29 (72 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
ProcEnviron:
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bash
SourcePackage: nvidia-graphics-drivers-440
UpgradeStatus: No upgrade log present (probably fresh install)
It turns out the MOK key installed previously was removed during a BIOS update. Upon the next kernel update from Ubuntu I was prompted to install the MOK key, after which OpenCL works even when kernel lockdown is enabled.