In the Linux kernel, the following vulnerability has been resolved:
drm/vc4: Prevent shader BO mappings from becoming writable
vc4_gem_object_mmap() rejects a writable mapping of a validated shader
BO, but leaves VM_MAYWRITE set. Userspace can map the BO read-only and
then turn it writable with mprotect().
Validated shader BOs must stay read-only: the validator checks the
instructions once and the GPU trusts them afterwards. A writable
mapping lets userspace rewrite the code after validation, bypassing the
validator.
Clear VM_MAYWRITE on the read-only path so the mapping cannot be
upgraded, as i915 already does for its read-only objects.
