[PATCH 3.16 041/136] arm64: vdso: fix clock_getres for 4GiB-aligned res

[Ben Hutchings]

3.16.54-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Mark Rutland <mark.rutland@xxxxxxx>

commit c80ed088a519da53f27b798a69748eaabc66aadf upstream.

The vdso tries to check for a NULL res pointer in __kernel_clock_getres,
but only checks the lower 32 bits as is uses CBZ on the W register the
res pointer is held in.

Thus, if the res pointer happened to be aligned to a 4GiB boundary, we'd
spuriously skip storing the timespec to it, while returning a zero error code
to the caller.

Prevent this by checking the whole pointer, using CBZ on the X register
the res pointer is held in.

Fixes: 9031fefde6f2ac1d ("arm64: VDSO support")
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Reported-by: Andrew Pinski <apinski@xxxxxxxxxx>
Reported-by: Mark Salyzyn <salyzyn@xxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/arm64/kernel/vdso/gettimeofday.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm64/kernel/vdso/gettimeofday.S
+++ b/arch/arm64/kernel/vdso/gettimeofday.S
@@ -186,7 +186,7 @@ ENTRY(__kernel_clock_getres)
 	b.ne	4f
 	ldr	x2, 6f
 2:
-	cbz	w1, 3f
+	cbz	x1, 3f
 	stp	xzr, x2, [x1]
 
 3:	/* res == NULL. */