CVE-2026-68445 drm/vc4: Prevent shader BO mappings from becoming writable

In the Linux kernel, the following vulnerability has been resolved: drm/vc4: Prevent shader BO mappings from becoming writable vc4gemobjectmmap rejects a writable mapping of a validated shader BO, but leaves VMMAYWRITE set. Userspace can map the BO read-only and then turn it writable with mprotec...