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authorThomas Gleixner <tglx@linutronix.de>2019-08-22 13:00:15 +0200
committerThomas Gleixner <tglx@linutronix.de>2019-08-23 02:12:11 +0200
commitb99328a60a482108f5195b4d611f90992ca016ba (patch)
tree694e2d7be207a6d3220e5346e8b94f470083656e /include
parent59c36bc8d377c8764eb617a92211e0fc2f1318da (diff)
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')
-rw-r--r--include/linux/timekeeper_internal.h5
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;