Commit 9b74d760 authored by Johannes Berg's avatar Johannes Berg Committed by Guo Mengqi
Browse files

um: time-travel: fix time corruption 

stable inclusion
from stable-v5.15.149
commit 0c7478a2da3f5fe106b4658338873d50c86ac7ab
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9DNRR
CVE: CVE-2023-52633

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c7478a2da3f5fe106b4658338873d50c86ac7ab



--------------------------------

[ Upstream commit abe4eaa8618bb36c2b33e9cdde0499296a23448c ]

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: default avatarVincent Whitchurch <Vincent.Whitchurch@axis.com>
Signed-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
Signed-off-by: default avatarRichard Weinberger <richard@nod.at>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
Signed-off-by: default avatarGuo Mengqi <guomengqi3@huawei.com>
parent 183e1907

arch/um/kernel/time.c

+27 −5
Original line number Diff line number Diff line
@@ -374,9 +374,29 @@ 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);
@@ -479,7 +499,11 @@ static int time_travel_connect_external(const char *socket) 
#define time_travel_start 0

#define time_travel_time 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)

{

}
@@ -624,9 +648,7 @@ static u64 timer_read(struct clocksource *cs) 
		 * to return from time_travel_update_time().

		 */

		if (!irqs_disabled() && !in_interrupt() && !in_softirq())

			time_travel_update_time(time_travel_time +

						TIMER_MULTIPLIER,

						false);

			time_travel_update_time_rel(TIMER_MULTIPLIER);

		return time_travel_time / TIMER_MULTIPLIER;

	}