diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2019-08-22 13:00:15 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2019-08-23 02:12:11 +0200 |
| commit | b99328a60a482108f5195b4d611f90992ca016ba (patch) | |
| tree | 694e2d7be207a6d3220e5346e8b94f470083656e /kernel/time/vsyscall.c | |
| parent | 59c36bc8d377c8764eb617a92211e0fc2f1318da (diff) | |
| download | linux-b99328a60a482108f5195b4d611f90992ca016ba.tar.bz2 | |
timekeeping/vsyscall: Prevent math overflow in BOOTTIME update
The VDSO update for CLOCK_BOOTTIME has a overflow issue as it shifts the
nanoseconds based boot time offset left by the clocksource shift. That
overflows once the boot time offset becomes large enough. As a consequence
CLOCK_BOOTTIME in the VDSO becomes a random number causing applications to
misbehave.
Fix it by storing a timespec64 representation of the offset when boot time
is adjusted and add that to the MONOTONIC base time value in the vdso data
page. Using the timespec64 representation avoids a 64bit division in the
update code.
Fixes: 44f57d788e7d ("timekeeping: Provide a generic update_vsyscall() implementation")
Reported-by: Chris Clayton <chris2553@googlemail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Chris Clayton <chris2553@googlemail.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908221257580.1983@nanos.tec.linutronix.de
Diffstat (limited to 'kernel/time/vsyscall.c')
| -rw-r--r-- | kernel/time/vsyscall.c | 22 |
1 files changed, 13 insertions, 9 deletions
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; |