CVE-2026-40290: OP-TEE has a Use-After-Free race in FF-A shared-memory teardown

OP-TEE is a Trusted Execution Environment (TEE) designed as companion to a non-secure Linux kernel running on Arm; Cortex-A cores using the TrustZone technology. Starting in version 3.16.0 and prior to 4.11.0, a user-after-free (UAF) race condition exists in the shared memory teardown logic of FF-A within OP-TEE SPMC/SP flows. This only applies when OP-TEE is configured as an SPMC for S-EL0 SPs, that is, with CFGSECUREPARTITION=y. The function spmemremove(), responsible for freeing entries in smem->receivers and smem->regions, fails to acquire the global spmemlock before performing the free() operations. Concurrently, other code paths, such as spmemgetreceiver(), iterate over these same lists without holding a lock, or, like spmemisshared(), iterate while holding the lock but are not serialized against the unprotected free() in spmemremove(). This creates a cross-thread race where a thread iterating the list can acquire a pointer to an entry (e.g., struct spmemmapregion or struct spmemreceiver), and then another thread calls spmemremove(), freeing the object. When the first thread resumes and dereferences the pointer, it results in a Use-After-Free vulnerability. Version 4.11.0 fixes the issue.