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    SubjectRe: [PATCH] timekeeping/vsyscall: Prevent math overflow in BOOTTIME update
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    Thanks Thomas.

    On 22/08/2019 12:00, Thomas Gleixner wrote:
    > 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.
    >

    I've tested resume from both suspend and hibernate and this patch fixes the problem I reported.

    Tested-by: Chris Clayton <chris2553@googlemail.com>

    > Fixes: 44f57d788e7d ("timekeeping: Provide a generic update_vsyscall() implementation")
    > Reported-by: Chris Clayton <chris2553@googlemail.com>
    > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    > ---
    > include/linux/timekeeper_internal.h | 5 +++++
    > kernel/time/timekeeping.c | 5 +++++
    > kernel/time/vsyscall.c | 22 +++++++++++++---------
    > 3 files changed, 23 insertions(+), 9 deletions(-)
    >
    > --- a/include/linux/timekeeper_internal.h
    > +++ b/include/linux/timekeeper_internal.h
    > @@ -57,6 +57,7 @@ struct tk_read_base {
    > * @cs_was_changed_seq: The sequence number of clocksource change events
    > * @next_leap_ktime: CLOCK_MONOTONIC time value of a pending leap-second
    > * @raw_sec: CLOCK_MONOTONIC_RAW time in seconds
    > + * @monotonic_to_boot: CLOCK_MONOTONIC to CLOCK_BOOTTIME offset
    > * @cycle_interval: Number of clock cycles in one NTP interval
    > * @xtime_interval: Number of clock shifted nano seconds in one NTP
    > * interval.
    > @@ -84,6 +85,9 @@ struct tk_read_base {
    > *
    > * wall_to_monotonic is no longer the boot time, getboottime must be
    > * used instead.
    > + *
    > + * @monotonic_to_boottime is a timespec64 representation of @offs_boot to
    > + * accelerate the VDSO update for CLOCK_BOOTTIME.
    > */
    > struct timekeeper {
    > struct tk_read_base tkr_mono;
    > @@ -99,6 +103,7 @@ struct timekeeper {
    > u8 cs_was_changed_seq;
    > ktime_t next_leap_ktime;
    > u64 raw_sec;
    > + struct timespec64 monotonic_to_boot;
    >
    > /* The following members are for timekeeping internal use */
    > u64 cycle_interval;
    > --- a/kernel/time/timekeeping.c
    > +++ b/kernel/time/timekeeping.c
    > @@ -146,6 +146,11 @@ static void tk_set_wall_to_mono(struct t
    > 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);
    > }
    >
    > /*
    > --- a/kernel/time/vsyscall.c
    > +++ b/kernel/time/vsyscall.c
    > @@ -17,7 +17,7 @@ static inline void update_vdso_data(stru
    > 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(stru
    > }
    > 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;
    >

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