diff options
author | Johannes Berg <johannes.berg@intel.com> | 2023-10-25 23:45:05 +0300 |
---|---|---|
committer | Richard Weinberger <richard@nod.at> | 2024-01-05 02:29:51 +0300 |
commit | abe4eaa8618bb36c2b33e9cdde0499296a23448c (patch) | |
tree | c1f1c3df07fbaded8ac87c696bda05532939223e /arch/um/kernel/time.c | |
parent | 7d748f60a4b82b50bf25fad1bd42d33f049f76aa (diff) | |
download | linux-abe4eaa8618bb36c2b33e9cdde0499296a23448c.tar.xz |
um: time-travel: fix time corruption
In 'basic' time-travel mode (without =inf-cpu or =ext), we
still get timer interrupts. These can happen at arbitrary
points in time, i.e. while in timer_read(), which pushes
time forward just a little bit. Then, if we happen to get
the interrupt after calculating the new time to push to,
but before actually finishing that, the interrupt will set
the time to a value that's incompatible with the forward,
and we'll crash because time goes backwards when we do the
forwarding.
Fix this by reading the time_travel_time, calculating the
adjustment, and doing the adjustment all with interrupts
disabled.
Reported-by: Vincent Whitchurch <Vincent.Whitchurch@axis.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Diffstat (limited to 'arch/um/kernel/time.c')
-rw-r--r-- | arch/um/kernel/time.c | 32 |
1 files changed, 27 insertions, 5 deletions
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c index fddd1dec27e6..3e270da6b6f6 100644 --- a/arch/um/kernel/time.c +++ b/arch/um/kernel/time.c @@ -432,9 +432,29 @@ static void time_travel_update_time(unsigned long long next, bool idle) time_travel_del_event(&ne); } +static void time_travel_update_time_rel(unsigned long long offs) +{ + unsigned long flags; + + /* + * Disable interrupts before calculating the new time so + * that a real timer interrupt (signal) can't happen at + * a bad time e.g. after we read time_travel_time but + * before we've completed updating the time. + */ + local_irq_save(flags); + time_travel_update_time(time_travel_time + offs, false); + local_irq_restore(flags); +} + void time_travel_ndelay(unsigned long nsec) { - time_travel_update_time(time_travel_time + nsec, false); + /* + * Not strictly needed to use _rel() version since this is + * only used in INFCPU/EXT modes, but it doesn't hurt and + * is more readable too. + */ + time_travel_update_time_rel(nsec); } EXPORT_SYMBOL(time_travel_ndelay); @@ -568,7 +588,11 @@ static void time_travel_set_start(void) #define time_travel_time 0 #define time_travel_ext_waiting 0 -static inline void time_travel_update_time(unsigned long long ns, bool retearly) +static inline void time_travel_update_time(unsigned long long ns, bool idle) +{ +} + +static inline void time_travel_update_time_rel(unsigned long long offs) { } @@ -720,9 +744,7 @@ static u64 timer_read(struct clocksource *cs) */ if (!irqs_disabled() && !in_interrupt() && !in_softirq() && !time_travel_ext_waiting) - time_travel_update_time(time_travel_time + - TIMER_MULTIPLIER, - false); + time_travel_update_time_rel(TIMER_MULTIPLIER); return time_travel_time / TIMER_MULTIPLIER; } |