[ Upstream commit 16171bff ]

Alex Shi reported the pkey macros above arch_set_user_pkey_access()
to be unused.  They are unused, and even refer to a nonexistent
CONFIG option.

But, they might have served a good use, which was to ensure that
the code does not try to set values that would not fit in the
PKRU register.  As it stands, a too-large 'pkey' value would
be likely to silently overflow the u32 new_pkru_bits.

Add a check to look for overflows.  Also add a comment to remind
any future developer to closely examine the types used to store
pkey values if arch_max_pkey() ever changes.

This boots and passes the x86 pkey selftests.
Reported-by: NAlex Shi <alex.shi@linux.alibaba.com>
Signed-off-by: NDave Hansen <dave.hansen@intel.com>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200122165346.AD4DA150@viggo.jf.intel.comSigned-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>