| From f01337197419b7e8a492e83089552b77d3b5fb90 Mon Sep 17 00:00:00 2001 |
| From: Juergen Gross <jgross@suse.com> |
| Date: Tue, 20 Oct 2020 06:52:55 +0200 |
| Subject: xen/events: fix race in evtchn_fifo_unmask() |
| |
| From: Juergen Gross <jgross@suse.com> |
| |
| 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@vger.kernel.org |
| Signed-off-by: Juergen Gross <jgross@suse.com> |
| Reviewed-by: Jan Beulich <jbeulich@suse.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| 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(evtchn |
| 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(evtchn_port_t port) |
| @@ -248,8 +254,7 @@ static void evtchn_fifo_unmask(evtchn_po |
| |
| 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); |
| } |