arm64: Support execute-only permissions with Enhanced PAN

mainline inclusion
from mainline-v5.13-rc1
commit 18107f8a
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4QUF2


CVE: NA

----------------------

Enhanced Privileged Access Never (EPAN) allows Privileged Access Never
to be used with Execute-only mappings.

Absence of such support was a reason for 24cecc37 ("arm64: Revert
support for execute-only user mappings"). Thus now it can be revisited
and re-enabled.

Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210312173811.58284-2-vladimir.murzin@arm.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

 Conflicts:
	arch/arm64/Kconfig
	arch/arm64/include/asm/cpucaps.h
[wangxiongfeng: fix conflicts caused by context mismatch.]
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>