From e5cb862284e7afa01673f8bd5057f834a5fe0d3a Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Mon, 14 Sep 2020 14:01:02 +0200 Subject: [PATCH] xen/events: block rogue events for some time In order to avoid high dom0 load due to rogue guests sending events at high frequency, block those events in case there was no action needed in dom0 to handle the events. This is done by adding a per-event counter, which set to zero in case an EOI without the XEN_EOI_FLAG_SPURIOUS is received from a backend driver, and incremented when this flag has been set. In case the counter is 2 or higher delay the EOI by 1 << (cnt - 2) jiffies, but not more than 1 second. In order not to waste memory shorten the per-event refcnt to two bytes (it should normally never exceed a value of 2). Add an overflow check to evtchn_get() to make sure the 2 bytes really won't overflow. This is part of XSA-332. Cc: stable@vger.kernel.org Signed-off-by: Juergen Gross Reviewed-by: Jan Beulich Reviewed-by: Stefano Stabellini Reviewed-by: Wei Liu --- drivers/xen/events/events_base.c | 27 ++++++++++++++++++++++----- drivers/xen/events/events_internal.h | 3 ++- 2 files changed, 24 insertions(+), 6 deletions(-) diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c index cde096a6f11d0..cc317739e7860 100644 --- a/drivers/xen/events/events_base.c +++ b/drivers/xen/events/events_base.c @@ -461,17 +461,34 @@ static void lateeoi_list_add(struct irq_info *info) spin_unlock_irqrestore(&eoi->eoi_list_lock, flags); } -static void xen_irq_lateeoi_locked(struct irq_info *info) +static void xen_irq_lateeoi_locked(struct irq_info *info, bool spurious) { evtchn_port_t evtchn; unsigned int cpu; + unsigned int delay = 0; evtchn = info->evtchn; if (!VALID_EVTCHN(evtchn) || !list_empty(&info->eoi_list)) return; + if (spurious) { + if ((1 << info->spurious_cnt) < (HZ << 2)) + info->spurious_cnt++; + if (info->spurious_cnt > 1) { + delay = 1 << (info->spurious_cnt - 2); + if (delay > HZ) + delay = HZ; + if (!info->eoi_time) + info->eoi_cpu = smp_processor_id(); + info->eoi_time = get_jiffies_64() + delay; + } + } else { + info->spurious_cnt = 0; + } + cpu = info->eoi_cpu; - if (info->eoi_time && info->irq_epoch == per_cpu(irq_epoch, cpu)) { + if (info->eoi_time && + (info->irq_epoch == per_cpu(irq_epoch, cpu) || delay)) { lateeoi_list_add(info); return; } @@ -508,7 +525,7 @@ static void xen_irq_lateeoi_worker(struct work_struct *work) info->eoi_time = 0; - xen_irq_lateeoi_locked(info); + xen_irq_lateeoi_locked(info, false); } if (info) @@ -537,7 +554,7 @@ void xen_irq_lateeoi(unsigned int irq, unsigned int eoi_flags) info = info_for_irq(irq); if (info) - xen_irq_lateeoi_locked(info); + xen_irq_lateeoi_locked(info, eoi_flags & XEN_EOI_FLAG_SPURIOUS); read_unlock_irqrestore(&evtchn_rwlock, flags); } @@ -1441,7 +1458,7 @@ int evtchn_get(evtchn_port_t evtchn) goto done; err = -EINVAL; - if (info->refcnt <= 0) + if (info->refcnt <= 0 || info->refcnt == SHRT_MAX) goto done; info->refcnt++; diff --git a/drivers/xen/events/events_internal.h b/drivers/xen/events/events_internal.h index aac05cf52ced8..82937d90d7d72 100644 --- a/drivers/xen/events/events_internal.h +++ b/drivers/xen/events/events_internal.h @@ -31,7 +31,8 @@ enum xen_irq_type { struct irq_info { struct list_head list; struct list_head eoi_list; - int refcnt; + short refcnt; + short spurious_cnt; enum xen_irq_type type; /* type */ unsigned irq; evtchn_port_t evtchn; /* event channel */ -- 2.39.5