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.
References
- https://git.kernel.org/stable/c/019e6ad247f7fd038d2e009789f6d9bfcccb1ae7
- https://git.kernel.org/stable/c/0c9e6367639548307d3f578f6943ce72c9d39087
- https://git.kernel.org/stable/c/6deaa317201851c644c431b57682e54d06b35838
- https://git.kernel.org/stable/c/9f0ee411fc2d76333d6087c5862ffa907cf7a175
- https://git.kernel.org/stable/c/fe168ef1d232d734d9998fd74822e2e20930dfff