arm64: Implement thread_struct whitelist for hardened usercopy
While ARM64 carries FPU state in the thread structure that is saved and
restored during signal handling, it doesn't need to declare a usercopy
whitelist, since existing accessors are all either using a bounce buffer
(for which whitelisting isn't checking the slab), are statically sized
(which will bypass the hardened usercopy check), or both.
Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: James Morse <james.morse@arm.com> Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org> Cc: Dave Martin <Dave.Martin@arm.com> Cc: zijun_hu <zijun_hu@htc.com> Cc: linux-arm-kernel@lists.infradead.org Signed-off-by: Kees Cook <keescook@chromium.org>