From the kernel's COPYING file: NOTE! This copyright does *not* cover user programs that use kernel services by normal system calls - this is mere

From the kernel's COPYING file: NOTE! This copyright does *not* cover user programs that use kernel services by normal system calls - this is merely considered normal use of the kernel, and does *not* fall under the heading of "derived work". As I read it, the non-Linux part of Android is entirely in user-space, and thus exempt from the terms of the GPL with respect to the kernel.