diff options
| author | Juergen Gross <jgross@suse.com> | 2020-10-20 06:52:55 +0200 |
|---|---|---|
| committer | Juergen Gross <jgross@suse.com> | 2020-10-20 10:21:58 +0200 |
| commit | f01337197419b7e8a492e83089552b77d3b5fb90 (patch) | |
| tree | d49649615f31a412be79528e3c3deb7985a8eb87 /drivers/xen | |
| parent | 4d3fe31bd993ef504350989786858aefdb877daa (diff) | |
xen/events: fix race in evtchn_fifo_unmask()
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>
Diffstat (limited to 'drivers/xen')
| -rw-r--r-- | drivers/xen/events/events_fifo.c | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c index c60ee0450173..7fd39c64d4b5 100644 --- 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_port_t port) 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_port_t port) 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); } |