From b99328a60a482108f5195b4d611f90992ca016ba Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 22 Aug 2019 13:00:15 +0200 Subject: 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 Signed-off-by: Thomas Gleixner Tested-by: Chris Clayton Tested-by: Vincenzo Frascino Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908221257580.1983@nanos.tec.linutronix.de --- include/linux/timekeeper_internal.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include') 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; -- cgit v1.2.3