x86, vdso, time: Cast tv_nsec to u64 for proper shifting in update_vsyscall()

With tk->wall_to_monotonic.tv_nsec being a 32-bit value on 32-bit
systems, (tk->wall_to_monotonic.tv_nsec << tk->shift) in update_vsyscall()
may lose upper bits or, worse, add them since compiler will do this:
	(u64)(tk->wall_to_monotonic.tv_nsec << tk->shift)
instead of
	((u64)tk->wall_to_monotonic.tv_nsec << tk->shift)

So if, for example, tv_nsec is 0x800000 and shift is 8 we will end up
with 0xffffffff80000000 instead of 0x80000000. And then we are stuck in
the subsequent 'while' loop.

We need an explicit cast.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: http://lkml.kernel.org/r/1399648287-15178-1-git-send-email-boris.ostrovsky@oracle.com
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: <stable@vger.kernel.org> # v3.14
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

diff --git a/arch/x86/kernel/vsyscall_gtod.c b/arch/x86/kernel/vsyscall_gtod.c
index f9c6e56e14b5f31229b75721db9975dac5fe58c9..9531fbb123ba2223257f48dd724b59a45289389c 100644 (file)
--- a/arch/x86/kernel/vsyscall_gtod.c
+++ b/arch/x86/kernel/vsyscall_gtod.c
@@ -43,7 +43,7 @@ void update_vsyscall(struct timekeeper *tk)
        vdata->monotonic_time_sec       = tk->xtime_sec
                                        + tk->wall_to_monotonic.tv_sec;
        vdata->monotonic_time_snsec     = tk->xtime_nsec
-                                       + (tk->wall_to_monotonic.tv_nsec
+                                       + ((u64)tk->wall_to_monotonic.tv_nsec
                                                << tk->shift);
        while (vdata->monotonic_time_snsec >=
                                        (((u64)NSEC_PER_SEC) << tk->shift)) {