Commit f08cae2f authored Apr 29, 2019 by Boyang Zhou Committed by Will Deacon Apr 29, 2019

arm64: mmap: Ensure file offset is treated as unsigned



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: Boyang Zhou <zhouby_cn@126.com>
[will: rewrote commit message]
Signed-off-by: Will Deacon <will.deacon@arm.com>

parent bc15cf70

arch/arm64/kernel/sys.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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;

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