arm64: mmap: Ensure file offset is treated as unsigned

mainline inclusion
from mainline-5.1-rc3
commit f08cae2f28db
category: bugfix
bugzilla: 14514
CVE: NA

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

The file offset argument to the arm64 sys_mmap() implementation is
scaled from bytes to pages by shifting right by PAGE_SHIFT.
Unfortunately, the offset is passed in as a signed 'off_t' type and
therefore large offsets (i.e. with the top bit set) are incorrectly
sign-extended by the shift. This has been observed to cause false mmap()
failures when mapping GPU doorbells on an arm64 server part.

Change the type of the file offset argument to sys_mmap() from 'off_t'
to 'unsigned long' so that the shifting scales the value as expected.

Cc: <stable@vger.kernel.org>
Signed-off-by: NBoyang Zhou <zhouby_cn@126.com>
[will: rewrote commit message]
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NXiongfeng Wang <wangxiongfeng2@huawei.com>
Reviewed-by: NYao Hongbo <yaohongbo@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

arch/arm64/kernel/sys.c

@@ -31,7 +31,7 @@
 
 SYSCALL_DEFINE6(mmap, unsigned long, addr, unsigned long, len,
 		unsigned long, prot, unsigned long, flags,
-		unsigned long, fd, off_t, off)
+		unsigned long, fd, unsigned long, off)
 {
 	if (offset_in_page(off) != 0)
 		return -EINVAL;