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| 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 /include/linux/timekeeper_internal.h | |
| parent | 59c36bc8d377c8764eb617a92211e0fc2f1318da (diff) | |
| download | lwn-b99328a60a482108f5195b4d611f90992ca016ba.tar.gz lwn-b99328a60a482108f5195b4d611f90992ca016ba.zip | |
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 'include/linux/timekeeper_internal.h')
| -rw-r--r-- | include/linux/timekeeper_internal.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h index 7acb953298a7..84ff2844df2a 100644 --- 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; |