The following commit has been merged into the timers/urgent branch of tip:
Commit-ID: b99328a60a482108f5195b4d611f90992ca016ba
Gitweb: https://git.kernel.org/tip/b99328a60a482108f5195b4d611f90992ca016ba
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Thu, 22 Aug 2019 13:00:15 +02:00
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Fri, 23 Aug 2019 02:12:11 +02:00
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@xxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Chris Clayton <chris2553@xxxxxxxxxxxxxx>
Tested-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908221257580.1983@xxxxxxxxxxxxxxxxxxxxxxx
---
include/linux/timekeeper_internal.h | 5 -----
kernel/time/timekeeping.c | 5 -----
kernel/time/vsyscall.c | 22 +++++++++-------------
3 files changed, 9 insertions(+), 23 deletions(-)
diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index 84ff284..7acb953 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -57,7 +57,6 @@ 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.
@@ -85,9 +84,6 @@ 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;
@@ -103,7 +99,6 @@ 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;
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index ca69290..d911c84 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -146,11 +146,6 @@ static void tk_set_wall_to_mono(struct timekeeper *tk, struct timespec64 wtm)
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);
}
/*
diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c
index 4bc37ac..8cf3596 100644
--- a/kernel/time/vsyscall.c
+++ b/kernel/time/vsyscall.c
@@ -17,7 +17,7 @@ static inline void update_vdso_data(struct vdso_data *vdata,
struct timekeeper *tk)
{
struct vdso_timestamp *vdso_ts;
- u64 nsec, sec;
+ u64 nsec;
vdata[CS_HRES_COARSE].cycle_last = tk->tkr_mono.cycle_last;
vdata[CS_HRES_COARSE].mask = tk->tkr_mono.mask;
@@ -45,27 +45,23 @@ static inline void update_vdso_data(struct vdso_data *vdata,
}
vdso_ts->nsec = 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_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_BOOTTIME */
vdso_ts = &vdata[CS_HRES_COARSE].basetime[CLOCK_BOOTTIME];
- vdso_ts->sec = sec;
-
+ 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);
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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