x86/kasan: Add helpers to align shadow addresses up and down

mainline inclusion
from mainline-v6.2-rc1
commit bde258d9
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I6C6UC
CVE: CVE-2023-0597

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=bde258d97409f2a45243cb393a55ea9ecfc7aba5



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Add helpers to dedup code for aligning shadow address up/down to page
boundaries when translating an address to its shadow.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Link: https://lkml.kernel.org/r/20221110203504.1985010-5-seanjc@google.com


Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
Reviewed-by: Chen Wandun <chenwandun@huawei.com>
Reviewed-by: Wang Weiyang <wangweiyang2@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>