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Commit b99328a6 authored by Thomas Gleixner's avatar Thomas Gleixner
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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: 44f57d78 ("timekeeping: Provide a generic update_vsyscall() implementation")
Reported-by: default avatarChris Clayton <chris2553@googlemail.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarChris Clayton <chris2553@googlemail.com>
Tested-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908221257580.1983@nanos.tec.linutronix.de
parent 59c36bc8
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