arm64: fix current_thread_info()->addr_limit setup

hulk inclusion
category: bugfix
bugzilla: 51408
CVE: NA

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At elf loading in flush_old_exec() in fs/exec.c, generic code sets
current_thread_info()->addr_limit to one that corresponds aarch64 value,
and ignores compat mode there as corresponding status setup happens
later on in load_elf_binary() by SET_PERSONALITY() macro. As result,
compat task has wrong addr_limit, and it may cause various bugs.

This patch fixes it. It also fixes USER_DS macro to return different
values depending on compat at runtime.

It was discovered during ilp32 development. See details here:
https://lkml.org/lkml/2016/5/11/975



v2:
flush tpidrro_el0 unconditionally in tls_thread_flush() as if exec() is
called by aarch64 task, is_compat_task() fails even if new thread is
aarch32.

Signed-off-by: Yury Norov <ynorov@caviumnetworks>
Signed-off-by: Zhou Chengming <zhouchengming1@huawei.com>
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>

 Conflicts:
	arch/arm64/include/asm/uaccess.h
	arch/arm64/kernel/process.c
	fs/exec.c
[wang: expand macro USER_DS in entry.S according to commit: ee20d8797f06
("arm64: Make USER_DS an inclusive limit")]
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Jiahao Chen <chenjiahao16@huawei.com>
Reviewed-by: Chang Liao <liaochang1@huawei.com>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>