[RFC 10/20] x86/vdso: Use set_normalized_timespec() to avoid 32 bit overflow

[Dmitry Safonov]

From: Andrei Vagin <ava...@gmail.com>

ts->tv_nsec + offset->tv_nsec

On 32 bit machines that sum can be larger than (1 << 31) and therefor
result in a negative value which screws up the result completely.

Signed-off-by: Andrei Vagin <ava...@openvz.org>
Signed-off-by: Dmitry Safonov <d...@arista.com>
---
 arch/x86/entry/vdso/vclock_gettime.c | 35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/arch/x86/entry/vdso/vclock_gettime.c 
b/arch/x86/entry/vdso/vclock_gettime.c
index 0594266740b9..a265e2737a9a 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -231,20 +231,37 @@ notrace static int __always_inline do_realtime(struct 
timespec *ts)
        return mode;
 }
 
+notrace void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
+{
+       while (nsec >= NSEC_PER_SEC) {
+               /*
+                * The following asm() prevents the compiler from
+                * optimising this loop into a modulo operation. See
+                * also __iter_div_u64_rem() in include/linux/time.h
+                */
+               asm("" : "+rm"(nsec));
+               nsec -= NSEC_PER_SEC;
+               ++sec;
+       }
+       while (nsec < 0) {
+               asm("" : "+rm"(nsec));
+               nsec += NSEC_PER_SEC;
+               --sec;
+       }
+       ts->tv_sec = sec;
+       ts->tv_nsec = nsec;
+}
+
 notrace static __always_inline void monotonic_to_ns(struct timespec *ts)
 {
 #ifdef CONFIG_TIME_NS
        struct timens_offsets *timens = (struct timens_offsets *) &timens_page;
+       struct timespec offset;
+
+       offset = timespec64_to_timespec(timens->monotonic_time_offset);
+
+       *ts = timespec_add(*ts, offset);
 
-       ts->tv_sec += timens->monotonic_time_offset.tv_sec;
-       ts->tv_nsec += timens->monotonic_time_offset.tv_nsec;
-       if (ts->tv_nsec > NSEC_PER_SEC) {
-               ts->tv_nsec -= NSEC_PER_SEC;
-               ts->tv_sec++;
-       } else if (ts->tv_nsec < 0) {
-               ts->tv_nsec += NSEC_PER_SEC;
-               ts->tv_sec--;
-       }
 #endif
 }
 
-- 
2.13.6