This is a note to let you know that I've just added the patch titled
xen/events: fix race in evtchn_fifo_unmask()
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
xen-events-fix-race-in-evtchn_fifo_unmask.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Tue Nov 17 12:38:50 PM CET 2020
From: Juergen Gross <jgross@xxxxxxxx>
Date: Tue, 3 Nov 2020 15:29:01 +0100
Subject: xen/events: fix race in evtchn_fifo_unmask()
To: stable@xxxxxxxxxxxxxxx
Message-ID: <20201103142911.21980-5-jgross@xxxxxxxx>
From: Juergen Gross <jgross@xxxxxxxx>
commit f01337197419b7e8a492e83089552b77d3b5fb90 upstream.
Unmasking a fifo event channel can result in unmasking it twice, once
directly in the kernel and once via a hypercall in case the event was
pending.
Fix that by doing the local unmask only if the event is not pending.
This is part of XSA-332.
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/xen/events/events_fifo.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -227,19 +227,25 @@ static bool evtchn_fifo_is_masked(unsign
return sync_test_bit(EVTCHN_FIFO_BIT(MASKED, word), BM(word));
}
/*
- * Clear MASKED, spinning if BUSY is set.
+ * Clear MASKED if not PENDING, spinning if BUSY is set.
+ * Return true if mask was cleared.
*/
-static void clear_masked(volatile event_word_t *word)
+static bool clear_masked_cond(volatile event_word_t *word)
{
event_word_t new, old, w;
w = *word;
do {
+ if (w & (1 << EVTCHN_FIFO_PENDING))
+ return false;
+
old = w & ~(1 << EVTCHN_FIFO_BUSY);
new = old & ~(1 << EVTCHN_FIFO_MASKED);
w = sync_cmpxchg(word, old, new);
} while (w != old);
+
+ return true;
}
static void evtchn_fifo_unmask(unsigned port)
@@ -248,8 +254,7 @@ static void evtchn_fifo_unmask(unsigned
BUG_ON(!irqs_disabled());
- clear_masked(word);
- if (evtchn_fifo_is_pending(port)) {
+ if (!clear_masked_cond(word)) {
struct evtchn_unmask unmask = { .port = port };
(void)HYPERVISOR_event_channel_op(EVTCHNOP_unmask, &unmask);
}
Patches currently in stable-queue which might be from jgross@xxxxxxxx are
queue-4.14/xen-blkback-use-lateeoi-irq-binding.patch
queue-4.14/xen-events-block-rogue-events-for-some-time.patch
queue-4.14/xen-pvcallsback-use-lateeoi-irq-binding.patch
queue-4.14/xen-events-fix-race-in-evtchn_fifo_unmask.patch
queue-4.14/xen-events-switch-user-event-channels-to-lateeoi-model.patch
queue-4.14/xen-events-defer-eoi-in-case-of-excessive-number-of-events.patch
queue-4.14/xen-events-add-a-new-late-eoi-evtchn-framework.patch
queue-4.14/xen-events-use-a-common-cpu-hotplug-hook-for-event-channels.patch
queue-4.14/xen-events-avoid-removing-an-event-channel-while-handling-it.patch
queue-4.14/xen-netback-use-lateeoi-irq-binding.patch
queue-4.14/xen-pciback-use-lateeoi-irq-binding.patch
queue-4.14/xen-events-add-a-proper-barrier-to-2-level-uevent-unmasking.patch
queue-4.14/xen-scsiback-use-lateeoi-irq-binding.patch
