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xen.17324
xsa343-3.patch
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File xsa343-3.patch of Package xen.17324
evtchn: address races with evtchn_reset() Neither d->evtchn_port_ops nor max_evtchns(d) may be used in an entirely lock-less manner, as both may change by a racing evtchn_reset(). In the common case, at least one of the domain's event lock or the per-channel lock needs to be held. In the specific case of the inter-domain sending by evtchn_send() and notify_via_xen_event_channel() holding the other side's per-channel lock is sufficient, as the channel can't change state without both per-channel locks held. Without such a channel changing state, evtchn_reset() can't complete successfully. Lock-free accesses continue to be permitted for the shim (calling some otherwise internal event channel functions), as this happens while the domain is in effectively single-threaded mode. Special care also needs taking for the shim's marking of in-use ports as ECS_RESERVED (allowing use of such ports in the shim case is okay because switching into and hence also out of FIFO mode is impossible there). As a side effect, certain operations on Xen bound event channels which were mistakenly permitted so far (e.g. unmask or poll) will be refused now. This is part of XSA-343. Signed-off-by: Jan Beulich <jbeulich@suse.com> Acked-by: Julien Grall <jgrall@amazon.com> --- a/xen/arch/x86/irq.c +++ b/xen/arch/x86/irq.c @@ -2323,14 +2323,24 @@ static void dump_irqs(unsigned char key) for ( i = 0; i < action->nr_guests; i++ ) { + struct evtchn *evtchn; + unsigned int pending = 2, masked = 2; + d = action->guest[i]; pirq = domain_irq_to_pirq(d, irq); info = pirq_info(d, pirq); + evtchn = evtchn_from_port(d, info->evtchn); + local_irq_disable(); + if ( spin_trylock(&evtchn->lock) ) + { + pending = evtchn_is_pending(d, evtchn); + masked = evtchn_is_masked(d, evtchn); + spin_unlock(&evtchn->lock); + } + local_irq_enable(); printk("%u:%3d(%c%c%c)", - d->domain_id, pirq, - evtchn_port_is_pending(d, info->evtchn) ? 'P' : '-', - evtchn_port_is_masked(d, info->evtchn) ? 'M' : '-', - (info->masked ? 'M' : '-')); + d->domain_id, pirq, "-P?"[pending], + "-M?"[masked], info->masked ? 'M' : '-'); if ( i != action->nr_guests ) printk(","); } --- a/xen/arch/x86/pv/shim.c +++ b/xen/arch/x86/pv/shim.c @@ -603,8 +603,11 @@ void pv_shim_inject_evtchn(unsigned int if ( port_is_valid(guest, port) ) { struct evtchn *chn = evtchn_from_port(guest, port); + unsigned long flags; + spin_lock_irqsave(&chn->lock, flags); evtchn_port_set_pending(guest, chn->notify_vcpu_id, chn); + spin_unlock_irqrestore(&chn->lock, flags); } } --- a/xen/common/event_2l.c +++ b/xen/common/event_2l.c @@ -63,8 +63,10 @@ static void evtchn_2l_unmask(struct doma } } -static bool evtchn_2l_is_pending(const struct domain *d, evtchn_port_t port) +static bool evtchn_2l_is_pending(const struct domain *d, + const struct evtchn *evtchn) { + evtchn_port_t port = evtchn->port; unsigned int max_ports = BITS_PER_EVTCHN_WORD(d) * BITS_PER_EVTCHN_WORD(d); ASSERT(port < max_ports); @@ -72,8 +74,10 @@ static bool evtchn_2l_is_pending(const s guest_test_bit(d, port, &shared_info(d, evtchn_pending))); } -static bool evtchn_2l_is_masked(const struct domain *d, evtchn_port_t port) +static bool evtchn_2l_is_masked(const struct domain *d, + const struct evtchn *evtchn) { + evtchn_port_t port = evtchn->port; unsigned int max_ports = BITS_PER_EVTCHN_WORD(d) * BITS_PER_EVTCHN_WORD(d); ASSERT(port < max_ports); --- a/xen/common/event_channel.c +++ b/xen/common/event_channel.c @@ -163,8 +163,9 @@ int evtchn_allocate_port(struct domain * if ( port_is_valid(d, port) ) { - if ( evtchn_from_port(d, port)->state != ECS_FREE || - evtchn_port_is_busy(d, port) ) + const struct evtchn *chn = evtchn_from_port(d, port); + + if ( chn->state != ECS_FREE || evtchn_is_busy(d, chn) ) return -EBUSY; } else @@ -777,6 +778,7 @@ void send_guest_vcpu_virq(struct vcpu *v unsigned long flags; int port; struct domain *d; + struct evtchn *chn; ASSERT(!virq_is_global(virq)); @@ -787,7 +789,10 @@ void send_guest_vcpu_virq(struct vcpu *v goto out; d = v->domain; - evtchn_port_set_pending(d, v->vcpu_id, evtchn_from_port(d, port)); + chn = evtchn_from_port(d, port); + spin_lock(&chn->lock); + evtchn_port_set_pending(d, v->vcpu_id, chn); + spin_unlock(&chn->lock); out: spin_unlock_irqrestore(&v->virq_lock, flags); @@ -816,7 +821,9 @@ static void send_guest_global_virq(struc goto out; chn = evtchn_from_port(d, port); + spin_lock(&chn->lock); evtchn_port_set_pending(d, chn->notify_vcpu_id, chn); + spin_unlock(&chn->lock); out: spin_unlock_irqrestore(&v->virq_lock, flags); @@ -826,6 +833,7 @@ void send_guest_pirq(struct domain *d, c { int port; struct evtchn *chn; + unsigned long flags; /* * PV guests: It should not be possible to race with __evtchn_close(). The @@ -840,7 +848,9 @@ void send_guest_pirq(struct domain *d, c } chn = evtchn_from_port(d, port); + spin_lock_irqsave(&chn->lock, flags); evtchn_port_set_pending(d, chn->notify_vcpu_id, chn); + spin_unlock_irqrestore(&chn->lock, flags); } static struct domain *global_virq_handlers[NR_VIRQS] __read_mostly; @@ -1036,12 +1046,15 @@ int evtchn_unmask(unsigned int port) { struct domain *d = current->domain; struct evtchn *evtchn; + unsigned long flags; if ( unlikely(!port_is_valid(d, port)) ) return -EINVAL; evtchn = evtchn_from_port(d, port); + spin_lock_irqsave(&evtchn->lock, flags); evtchn_port_unmask(d, evtchn); + spin_unlock_irqrestore(&evtchn->lock, flags); return 0; } @@ -1454,8 +1467,8 @@ static void domain_dump_evtchn_info(stru printk(" %4u [%d/%d/", port, - evtchn_port_is_pending(d, port), - evtchn_port_is_masked(d, port)); + evtchn_is_pending(d, chn), + evtchn_is_masked(d, chn)); evtchn_port_print_state(d, chn); printk("]: s=%d n=%d x=%d", chn->state, chn->notify_vcpu_id, chn->xen_consumer); --- a/xen/common/event_fifo.c +++ b/xen/common/event_fifo.c @@ -295,23 +295,26 @@ static void evtchn_fifo_unmask(struct do evtchn_fifo_set_pending(v, evtchn); } -static bool evtchn_fifo_is_pending(const struct domain *d, evtchn_port_t port) +static bool evtchn_fifo_is_pending(const struct domain *d, + const struct evtchn *evtchn) { - const event_word_t *word = evtchn_fifo_word_from_port(d, port); + const event_word_t *word = evtchn_fifo_word_from_port(d, evtchn->port); return word && guest_test_bit(d, EVTCHN_FIFO_PENDING, word); } -static bool_t evtchn_fifo_is_masked(const struct domain *d, evtchn_port_t port) +static bool_t evtchn_fifo_is_masked(const struct domain *d, + const struct evtchn *evtchn) { - const event_word_t *word = evtchn_fifo_word_from_port(d, port); + const event_word_t *word = evtchn_fifo_word_from_port(d, evtchn->port); return !word || guest_test_bit(d, EVTCHN_FIFO_MASKED, word); } -static bool_t evtchn_fifo_is_busy(const struct domain *d, evtchn_port_t port) +static bool_t evtchn_fifo_is_busy(const struct domain *d, + const struct evtchn *evtchn) { - const event_word_t *word = evtchn_fifo_word_from_port(d, port); + const event_word_t *word = evtchn_fifo_word_from_port(d, evtchn->port); return word && guest_test_bit(d, EVTCHN_FIFO_LINKED, word); } --- a/xen/include/asm-x86/event.h +++ b/xen/include/asm-x86/event.h @@ -47,4 +47,10 @@ static inline int arch_virq_is_global(ui return 1; } +#ifdef CONFIG_PV_SHIM +# include <asm/pv/shim.h> +# define arch_evtchn_is_special(chn) \ + (pv_shim && (chn)->port && (chn)->state == ECS_RESERVED) +#endif + #endif --- a/xen/include/xen/event.h +++ b/xen/include/xen/event.h @@ -125,6 +125,24 @@ static inline struct evtchn *evtchn_from return bucket_from_port(d, p) + (p % EVTCHNS_PER_BUCKET); } +/* + * "usable" as in "by a guest", i.e. Xen consumed channels are assumed to be + * taken care of separately where used for Xen's internal purposes. + */ +static bool evtchn_usable(const struct evtchn *evtchn) +{ + if ( evtchn->xen_consumer ) + return false; + +#ifdef arch_evtchn_is_special + if ( arch_evtchn_is_special(evtchn) ) + return true; +#endif + + BUILD_BUG_ON(ECS_FREE > ECS_RESERVED); + return evtchn->state > ECS_RESERVED; +} + /* Wait on a Xen-attached event channel. */ #define wait_on_xen_event_channel(port, condition) \ do { \ @@ -157,19 +175,24 @@ int evtchn_reset(struct domain *d); /* * Low-level event channel port ops. + * + * All hooks have to be called with a lock held which prevents the channel + * from changing state. This may be the domain event lock, the per-channel + * lock, or in the case of sending interdomain events also the other side's + * per-channel lock. Exceptions apply in certain cases for the PV shim. */ struct evtchn_port_ops { void (*init)(struct domain *d, struct evtchn *evtchn); void (*set_pending)(struct vcpu *v, struct evtchn *evtchn); void (*clear_pending)(struct domain *d, struct evtchn *evtchn); void (*unmask)(struct domain *d, struct evtchn *evtchn); - bool (*is_pending)(const struct domain *d, evtchn_port_t port); - bool (*is_masked)(const struct domain *d, evtchn_port_t port); + bool (*is_pending)(const struct domain *d, const struct evtchn *evtchn); + bool (*is_masked)(const struct domain *d, const struct evtchn *evtchn); /* * Is the port unavailable because it's still being cleaned up * after being closed? */ - bool (*is_busy)(const struct domain *d, evtchn_port_t port); + bool (*is_busy)(const struct domain *d, const struct evtchn *evtchn); int (*set_priority)(struct domain *d, struct evtchn *evtchn, unsigned int priority); void (*print_state)(struct domain *d, const struct evtchn *evtchn); @@ -185,38 +208,67 @@ static inline void evtchn_port_set_pendi unsigned int vcpu_id, struct evtchn *evtchn) { - d->evtchn_port_ops->set_pending(d->vcpu[vcpu_id], evtchn); + if ( evtchn_usable(evtchn) ) + d->evtchn_port_ops->set_pending(d->vcpu[vcpu_id], evtchn); } static inline void evtchn_port_clear_pending(struct domain *d, struct evtchn *evtchn) { - d->evtchn_port_ops->clear_pending(d, evtchn); + if ( evtchn_usable(evtchn) ) + d->evtchn_port_ops->clear_pending(d, evtchn); } static inline void evtchn_port_unmask(struct domain *d, struct evtchn *evtchn) { - d->evtchn_port_ops->unmask(d, evtchn); + if ( evtchn_usable(evtchn) ) + d->evtchn_port_ops->unmask(d, evtchn); } -static inline bool evtchn_port_is_pending(const struct domain *d, - evtchn_port_t port) +static inline bool evtchn_is_pending(const struct domain *d, + const struct evtchn *evtchn) { - return d->evtchn_port_ops->is_pending(d, port); + return evtchn_usable(evtchn) && d->evtchn_port_ops->is_pending(d, evtchn); } -static inline bool evtchn_port_is_masked(const struct domain *d, - evtchn_port_t port) +static inline bool evtchn_port_is_pending(struct domain *d, evtchn_port_t port) { - return d->evtchn_port_ops->is_masked(d, port); + struct evtchn *evtchn = evtchn_from_port(d, port); + bool rc; + unsigned long flags; + + spin_lock_irqsave(&evtchn->lock, flags); + rc = evtchn_is_pending(d, evtchn); + spin_unlock_irqrestore(&evtchn->lock, flags); + + return rc; +} + +static inline bool evtchn_is_masked(const struct domain *d, + const struct evtchn *evtchn) +{ + return !evtchn_usable(evtchn) || d->evtchn_port_ops->is_masked(d, evtchn); +} + +static inline bool evtchn_port_is_masked(struct domain *d, evtchn_port_t port) +{ + struct evtchn *evtchn = evtchn_from_port(d, port); + bool rc; + unsigned long flags; + + spin_lock_irqsave(&evtchn->lock, flags); + rc = evtchn_is_masked(d, evtchn); + spin_unlock_irqrestore(&evtchn->lock, flags); + + return rc; } -static inline bool evtchn_port_is_busy(const struct domain *d, - evtchn_port_t port) +static inline bool evtchn_is_busy(const struct domain *d, + const struct evtchn *evtchn) { return d->evtchn_port_ops->is_busy && - d->evtchn_port_ops->is_busy(d, port); + d->evtchn_port_ops->is_busy(d, evtchn); } static inline int evtchn_port_set_priority(struct domain *d, @@ -225,6 +277,8 @@ static inline int evtchn_port_set_priori { if ( !d->evtchn_port_ops->set_priority ) return -ENOSYS; + if ( !evtchn_usable(evtchn) ) + return -EACCES; return d->evtchn_port_ops->set_priority(d, evtchn, priority); }
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