CVE-2026-10669 Xtensa MPU `arch_buffer_validate()` integer-overflow lets a user thread bypass syscall pointer validation

On Xtensa SoCs built with CONFIGXTENSAMPU and CONFIGUSERSPACE, archbuffervalidate in arch/xtensa/core/mpu.c — the architecture hook that verifies a user-mode-supplied buffer is accessible to the calling user thread with the requested permission — defaulted its return value to 0 access permitted a...