CVE-2026-90586CVE-2026-90586

The Xtensa MMU userspace port never initialized the per-thread page-table pointer thread->arch.ptables during thread setup, while arch_mem_domain_thread_add() in arch/xtensa/core/ptables.c uses a non-NULL value of that field as its "this thread is migrating from another memory domain" predicate. For a thread whose struct k_thread backing memory is not zeroed, the field holds stale data and the kernel takes the migration branch, passing that stale value to reset_region() as the base of a level-1 page table. The equivalent field on x86 is explicitly cleared in z_x86_userspace_prepare_thread() for exactly this reason; the Xtensa port adopted the predicate without the initialization. The condition is reachable from an unprivileged user-mode thread on a build with CONFIG_XTENSA_MMU, CONFIG_USERSPACE and dynamically allocated kernel objects. k_object_alloc(K_OBJ_THREAD) is a system call and allocates the thread object from the caller's resource pool without zeroing it, and the k_thread_crea