Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timekeeping fix from Thomas Gleixner:
 "A single fix for a regression caused by the generic VDSO
  implementation where a math overflow causes CLOCK_BOOTTIME to become a
  random number generator"

* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  timekeeping/vsyscall: Prevent math overflow in BOOTTIME update

2 files changed, 18 insertions, 9 deletions

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index d911c8470149..ca69290bee2a 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -146,6 +146,11 @@ static void tk_set_wall_to_mono(struct timekeeper *tk, struct timespec64 wtm)
 static inline void tk_update_sleep_time(struct timekeeper *tk, ktime_t delta)
 {
 	tk->offs_boot = ktime_add(tk->offs_boot, delta);
+	/*
+	 * Timespec representation for VDSO update to avoid 64bit division
+	 * on every update.
+	 */
+	tk->monotonic_to_boot = ktime_to_timespec64(tk->offs_boot);
 }
 
 /*
diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c
index 8cf3596a4ce6..4bc37ac3bb05 100644
--- a/kernel/time/vsyscall.c
+++ b/kernel/time/vsyscall.c
@@ -17,7 +17,7 @@ static inline void update_vdso_data(struct vdso_data *vdata,
 				    struct timekeeper *tk)
 {
 	struct vdso_timestamp *vdso_ts;
-	u64 nsec;
+	u64 nsec, sec;
 
 	vdata[CS_HRES_COARSE].cycle_last	= tk->tkr_mono.cycle_last;
 	vdata[CS_HRES_COARSE].mask		= tk->tkr_mono.mask;
@@ -45,23 +45,27 @@ static inline void update_vdso_data(struct vdso_data *vdata,
 	}
 	vdso_ts->nsec	= nsec;
 
-	/* CLOCK_MONOTONIC_RAW */
-	vdso_ts		= &vdata[CS_RAW].basetime[CLOCK_MONOTONIC_RAW];
-	vdso_ts->sec	= tk->raw_sec;
-	vdso_ts->nsec	= tk->tkr_raw.xtime_nsec;
+	/* Copy MONOTONIC time for BOOTTIME */
+	sec	= vdso_ts->sec;
+	/* Add the boot offset */
+	sec	+= tk->monotonic_to_boot.tv_sec;
+	nsec	+= (u64)tk->monotonic_to_boot.tv_nsec << tk->tkr_mono.shift;
 
 	/* CLOCK_BOOTTIME */
 	vdso_ts		= &vdata[CS_HRES_COARSE].basetime[CLOCK_BOOTTIME];
-	vdso_ts->sec	= tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
-	nsec = tk->tkr_mono.xtime_nsec;
-	nsec += ((u64)(tk->wall_to_monotonic.tv_nsec +
-		       ktime_to_ns(tk->offs_boot)) << tk->tkr_mono.shift);
+	vdso_ts->sec	= sec;
+
 	while (nsec >= (((u64)NSEC_PER_SEC) << tk->tkr_mono.shift)) {
 		nsec -= (((u64)NSEC_PER_SEC) << tk->tkr_mono.shift);
 		vdso_ts->sec++;
 	}
 	vdso_ts->nsec	= nsec;
 
+	/* CLOCK_MONOTONIC_RAW */
+	vdso_ts		= &vdata[CS_RAW].basetime[CLOCK_MONOTONIC_RAW];
+	vdso_ts->sec	= tk->raw_sec;
+	vdso_ts->nsec	= tk->tkr_raw.xtime_nsec;
+
 	/* CLOCK_TAI */
 	vdso_ts		= &vdata[CS_HRES_COARSE].basetime[CLOCK_TAI];
 	vdso_ts->sec	= tk->xtime_sec + (s64)tk->tai_offset;