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Tsirkin" To: Jason Wang Cc: virtualization , linux-kernel , Marc Zyngier , Thomas Gleixner , Peter Zijlstra , Stefano Garzarella , Keir Fraser , "Paul E. McKenney" Subject: Re: Message-ID: <20220329100111-mutt-send-email-mst@kernel.org> References: <20220325050947-mutt-send-email-mst@kernel.org> <20220325060659-mutt-send-email-mst@kernel.org> <20220328015757-mutt-send-email-mst@kernel.org> <20220328062452-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 29, 2022 at 03:12:14PM +0800, Jason Wang wrote: > > > > > > And requesting irq commits all memory otherwise all drivers would be > > > > > > broken, > > > > > > > > > > So I think we might talk different issues: > > > > > > > > > > 1) Whether request_irq() commits the previous setups, I think the > > > > > answer is yes, since the spin_unlock of desc->lock (release) can > > > > > guarantee this though there seems no documentation around > > > > > request_irq() to say this. > > > > > > > > > > And I can see at least drivers/video/fbdev/omap2/omapfb/dss/dispc.c is > > > > > using smp_wmb() before the request_irq(). > > > > > > > > > > And even if write is ordered we still need read to be ordered to be > > > > > paired with that. > > > > IMO it synchronizes with the CPU to which irq is > > delivered. Otherwise basically all drivers would be broken, > > wouldn't they be? > > I guess it's because most of the drivers don't care much about the > buggy/malicious device. And most of the devices may require an extra > step to enable device IRQ after request_irq(). Or it's the charge of > the driver to do the synchronization. It is true that the use-case of malicious devices is somewhat boutique. But I think most drivers do want to have their hotplug routines to be robust, yes. > > I don't know whether it's correct on all platforms, but if not > > we need to fix request_irq. > > > > > > > > > > > > > if it doesn't it just needs to be fixed, not worked around in > > > > > > virtio. > > > > > > > > > > 2) virtio drivers might do a lot of setups between request_irq() and > > > > > virtio_device_ready(): > > > > > > > > > > request_irq() > > > > > driver specific setups > > > > > virtio_device_ready() > > > > > > > > > > CPU 0 probe) request_irq() > > > > > CPU 1 IRQ handler) read the uninitialized variable > > > > > CPU 0 probe) driver specific setups > > > > > CPU 0 probe) smp_store_release(intr_soft_enabled, true), commit the setups > > > > > CPU 1 IRQ handler) read irq_soft_enable as true > > > > > CPU 1 IRQ handler) use the uninitialized variable > > > > > > > > > > Thanks > > > > > > > > > > > > As I said, virtio_device_ready needs to do synchronize_irq. > > > > That will guarantee all setup is visible to the specific IRQ, > > > > > > Only the interrupt after synchronize_irq() returns. > > > > Anything else is a buggy device though. > > Yes, but the goal of this patch is to prevent the possible attack from > buggy(malicious) devices. Right. However if a driver of a *buggy* device somehow sees driver_ok = false even though it's actually initialized, that is not a deal breaker as that does not open us up to an attack. > > > > > >this > > > > is what it's point is. > > > > > > What happens if an interrupt is raised in the middle like: > > > > > > smp_store_release(dev->irq_soft_enabled, true) > > > IRQ handler > > > synchornize_irq() > > > > > > If we don't enforce a reading order, the IRQ handler may still see the > > > uninitialized variable. > > > > > > Thanks > > > > IMHO variables should be initialized before request_irq > > to a value meaning "not a valid interrupt". > > Specifically driver_ok = false. > > Handler in the scenario you describe will then see !driver_ok > > and exit immediately. > > So just to make sure we're on the same page. > > 1) virtio_reset_device() will set the driver_ok to false; > 2) virtio_device_ready() will set the driver_ok to true > > So for virtio drivers, it often did: > > 1) virtio_reset_device() > 2) find_vqs() which will call request_irq() > 3) other driver specific setups > 4) virtio_device_ready() > > In virtio_device_ready(), the patch perform the following currently: > > smp_store_release(driver_ok, true); > set_status(DRIVER_OK); > > Per your suggestion, to add synchronize_irq() after > smp_store_release() so we had > > smp_store_release(driver_ok, true); > synchornize_irq() > set_status(DRIVER_OK) > > Suppose there's a interrupt raised before the synchronize_irq(), if we do: > > if (READ_ONCE(driver_ok)) { > vq->callback() > } > > It will see the driver_ok as true but how can we make sure > vq->callback sees the driver specific setups (3) above? > > And an example is virtio_scsi(): > > virtio_reset_device() > virtscsi_probe() > virtscsi_init() > virtio_find_vqs() > ... > virtscsi_init_vq(&vscsi->event_vq, vqs[1]) > .... > virtio_device_ready() > > In virtscsi_event_done(): > > virtscsi_event_done(): > virtscsi_vq_done(vscsi, &vscsi->event_vq, ...); > > We need to make sure the even_done reads driver_ok before read vscsi->event_vq. > > Thanks See response by Thomas. A simple if (!dev->driver_ok) should be enough, it's all under a lock. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > We use smp_store_relase() > > > > > > > > > to make sure the driver commits the setup before enabling the irq. It > > > > > > > > > means the read needs to be ordered as well in vring_interrupt(). > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Although I couldn't find anything about this in memory-barriers.txt > > > > > > > > > > which surprises me. > > > > > > > > > > > > > > > > > > > > CC Paul to help make sure I'm right. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > To avoid breaking legacy device which can send IRQ before DRIVER_OK, a > > > > > > > > > > > > > module parameter is introduced to enable the hardening so function > > > > > > > > > > > > > hardening is disabled by default. > > > > > > > > > > > > Which devices are these? How come they send an interrupt before there > > > > > > > > > > > > are any buffers in any queues? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I copied this from the commit log for 22b7050a024d7 > > > > > > > > > > > > > > > > > > > > > > " > > > > > > > > > > > > > > > > > > > > > > This change will also benefit old hypervisors (before 2009) > > > > > > > > > > > that send interrupts without checking DRIVER_OK: previously, > > > > > > > > > > > the callback could race with driver-specific initialization. > > > > > > > > > > > " > > > > > > > > > > > > > > > > > > > > > > If this is only for config interrupt, I can remove the above log. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > This is only for config interrupt. > > > > > > > > > > > > > > > > > > Ok. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Note that the hardening is only done for vring interrupt since the > > > > > > > > > > > > > config interrupt hardening is already done in commit 22b7050a024d7 > > > > > > > > > > > > > ("virtio: defer config changed notifications"). But the method that is > > > > > > > > > > > > > used by config interrupt can't be reused by the vring interrupt > > > > > > > > > > > > > handler because it uses spinlock to do the synchronization which is > > > > > > > > > > > > > expensive. > > > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Jason Wang > > > > > > > > > > > > > > > > > > > > > > > > > --- > > > > > > > > > > > > > drivers/virtio/virtio.c | 19 +++++++++++++++++++ > > > > > > > > > > > > > drivers/virtio/virtio_ring.c | 9 ++++++++- > > > > > > > > > > > > > include/linux/virtio.h | 4 ++++ > > > > > > > > > > > > > include/linux/virtio_config.h | 25 +++++++++++++++++++++++++ > > > > > > > > > > > > > 4 files changed, 56 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c > > > > > > > > > > > > > index 8dde44ea044a..85e331efa9cc 100644 > > > > > > > > > > > > > --- a/drivers/virtio/virtio.c > > > > > > > > > > > > > +++ b/drivers/virtio/virtio.c > > > > > > > > > > > > > @@ -7,6 +7,12 @@ > > > > > > > > > > > > > #include > > > > > > > > > > > > > #include > > > > > > > > > > > > > +static bool irq_hardening = false; > > > > > > > > > > > > > + > > > > > > > > > > > > > +module_param(irq_hardening, bool, 0444); > > > > > > > > > > > > > +MODULE_PARM_DESC(irq_hardening, > > > > > > > > > > > > > + "Disalbe IRQ software processing when it is not expected"); > > > > > > > > > > > > > + > > > > > > > > > > > > > /* Unique numbering for virtio devices. */ > > > > > > > > > > > > > static DEFINE_IDA(virtio_index_ida); > > > > > > > > > > > > > @@ -220,6 +226,15 @@ static int virtio_features_ok(struct virtio_device *dev) > > > > > > > > > > > > > * */ > > > > > > > > > > > > > void virtio_reset_device(struct virtio_device *dev) > > > > > > > > > > > > > { > > > > > > > > > > > > > + /* > > > > > > > > > > > > > + * The below synchronize_rcu() guarantees that any > > > > > > > > > > > > > + * interrupt for this line arriving after > > > > > > > > > > > > > + * synchronize_rcu() has completed is guaranteed to see > > > > > > > > > > > > > + * irq_soft_enabled == false. > > > > > > > > > > > > News to me I did not know synchronize_rcu has anything to do > > > > > > > > > > > > with interrupts. Did not you intend to use synchronize_irq? > > > > > > > > > > > > I am not even 100% sure synchronize_rcu is by design a memory barrier > > > > > > > > > > > > though it's most likely is ... > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > According to the comment above tree RCU version of synchronize_rcu(): > > > > > > > > > > > > > > > > > > > > > > """ > > > > > > > > > > > > > > > > > > > > > > * RCU read-side critical sections are delimited by rcu_read_lock() > > > > > > > > > > > * and rcu_read_unlock(), and may be nested. In addition, but only in > > > > > > > > > > > * v5.0 and later, regions of code across which interrupts, preemption, > > > > > > > > > > > * or softirqs have been disabled also serve as RCU read-side critical > > > > > > > > > > > * sections. This includes hardware interrupt handlers, softirq handlers, > > > > > > > > > > > * and NMI handlers. > > > > > > > > > > > """ > > > > > > > > > > > > > > > > > > > > > > So interrupt handlers are treated as read-side critical sections. > > > > > > > > > > > > > > > > > > > > > > And it has the comment for explain the barrier: > > > > > > > > > > > > > > > > > > > > > > """ > > > > > > > > > > > > > > > > > > > > > > * Note that this guarantee implies further memory-ordering guarantees. > > > > > > > > > > > * On systems with more than one CPU, when synchronize_rcu() returns, > > > > > > > > > > > * each CPU is guaranteed to have executed a full memory barrier since > > > > > > > > > > > * the end of its last RCU read-side critical section whose beginning > > > > > > > > > > > * preceded the call to synchronize_rcu(). In addition, each CPU having > > > > > > > > > > > """ > > > > > > > > > > > > > > > > > > > > > > So on SMP it provides a full barrier. And for UP/tiny RCU we don't need the > > > > > > > > > > > barrier, if the interrupt come after WRITE_ONCE() it will see the > > > > > > > > > > > irq_soft_enabled as false. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > You are right. So then > > > > > > > > > > 1. I do not think we need load_acquire - why is it needed? Just > > > > > > > > > > READ_ONCE should do. > > > > > > > > > > > > > > > > > > See above. > > > > > > > > > > > > > > > > > > > 2. isn't synchronize_irq also doing the same thing? > > > > > > > > > > > > > > > > > > > > > > > > > > > Yes, but it requires a config ops since the IRQ knowledge is transport specific. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > + */ > > > > > > > > > > > > > + WRITE_ONCE(dev->irq_soft_enabled, false); > > > > > > > > > > > > > + synchronize_rcu(); > > > > > > > > > > > > > + > > > > > > > > > > > > > dev->config->reset(dev); > > > > > > > > > > > > > } > > > > > > > > > > > > > EXPORT_SYMBOL_GPL(virtio_reset_device); > > > > > > > > > > > > Please add comment explaining where it will be enabled. > > > > > > > > > > > > Also, we *really* don't need to synch if it was already disabled, > > > > > > > > > > > > let's not add useless overhead to the boot sequence. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Ok. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > @@ -427,6 +442,10 @@ int register_virtio_device(struct virtio_device *dev) > > > > > > > > > > > > > spin_lock_init(&dev->config_lock); > > > > > > > > > > > > > dev->config_enabled = false; > > > > > > > > > > > > > dev->config_change_pending = false; > > > > > > > > > > > > > + dev->irq_soft_check = irq_hardening; > > > > > > > > > > > > > + > > > > > > > > > > > > > + if (dev->irq_soft_check) > > > > > > > > > > > > > + dev_info(&dev->dev, "IRQ hardening is enabled\n"); > > > > > > > > > > > > > /* We always start by resetting the device, in case a previous > > > > > > > > > > > > > * driver messed it up. This also tests that code path a little. */ > > > > > > > > > > > > one of the points of hardening is it's also helpful for buggy > > > > > > > > > > > > devices. this flag defeats the purpose. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Do you mean: > > > > > > > > > > > > > > > > > > > > > > 1) we need something like config_enable? This seems not easy to be > > > > > > > > > > > implemented without obvious overhead, mainly the synchronize with the > > > > > > > > > > > interrupt handlers > > > > > > > > > > > > > > > > > > > > But synchronize is only on tear-down path. That is not critical for any > > > > > > > > > > users at the moment, even less than probe. > > > > > > > > > > > > > > > > > > I meant if we have vq->irq_pending, we need to call vring_interrupt() > > > > > > > > > in the virtio_device_ready() and synchronize the IRQ handlers with > > > > > > > > > spinlock or others. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 2) enable this by default, so I don't object, but this may have some risk > > > > > > > > > > > for old hypervisors > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The risk if there's a driver adding buffers without setting DRIVER_OK. > > > > > > > > > > > > > > > > > > Probably not, we have devices that accept random inputs from outside, > > > > > > > > > net, console, input etc. I've done a round of audits of the Qemu > > > > > > > > > codes. They look all fine since day0. > > > > > > > > > > > > > > > > > > > So with this approach, how about we rename the flag "driver_ok"? > > > > > > > > > > And then add_buf can actually test it and BUG_ON if not there (at least > > > > > > > > > > in the debug build). > > > > > > > > > > > > > > > > > > This looks like a hardening of the driver in the core instead of the > > > > > > > > > device. I think it can be done but in a separate series. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > And going down from there, how about we cache status in the > > > > > > > > > > device? Then we don't need to keep re-reading it every time, > > > > > > > > > > speeding boot up a tiny bit. > > > > > > > > > > > > > > > > > > I don't fully understand here, actually spec requires status to be > > > > > > > > > read back for validation in many cases. > > > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > > > > > > > > > > > > index 962f1477b1fa..0170f8c784d8 100644 > > > > > > > > > > > > > --- a/drivers/virtio/virtio_ring.c > > > > > > > > > > > > > +++ b/drivers/virtio/virtio_ring.c > > > > > > > > > > > > > @@ -2144,10 +2144,17 @@ static inline bool more_used(const struct vring_virtqueue *vq) > > > > > > > > > > > > > return vq->packed_ring ? more_used_packed(vq) : more_used_split(vq); > > > > > > > > > > > > > } > > > > > > > > > > > > > -irqreturn_t vring_interrupt(int irq, void *_vq) > > > > > > > > > > > > > +irqreturn_t vring_interrupt(int irq, void *v) > > > > > > > > > > > > > { > > > > > > > > > > > > > + struct virtqueue *_vq = v; > > > > > > > > > > > > > + struct virtio_device *vdev = _vq->vdev; > > > > > > > > > > > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > > > > > > > > + if (!virtio_irq_soft_enabled(vdev)) { > > > > > > > > > > > > > + dev_warn_once(&vdev->dev, "virtio vring IRQ raised before DRIVER_OK"); > > > > > > > > > > > > > + return IRQ_NONE; > > > > > > > > > > > > > + } > > > > > > > > > > > > > + > > > > > > > > > > > > > if (!more_used(vq)) { > > > > > > > > > > > > > pr_debug("virtqueue interrupt with no work for %p\n", vq); > > > > > > > > > > > > > return IRQ_NONE; > > > > > > > > > > > > > diff --git a/include/linux/virtio.h b/include/linux/virtio.h > > > > > > > > > > > > > index 5464f398912a..957d6ad604ac 100644 > > > > > > > > > > > > > --- a/include/linux/virtio.h > > > > > > > > > > > > > +++ b/include/linux/virtio.h > > > > > > > > > > > > > @@ -95,6 +95,8 @@ dma_addr_t virtqueue_get_used_addr(struct virtqueue *vq); > > > > > > > > > > > > > * @failed: saved value for VIRTIO_CONFIG_S_FAILED bit (for restore) > > > > > > > > > > > > > * @config_enabled: configuration change reporting enabled > > > > > > > > > > > > > * @config_change_pending: configuration change reported while disabled > > > > > > > > > > > > > + * @irq_soft_check: whether or not to check @irq_soft_enabled > > > > > > > > > > > > > + * @irq_soft_enabled: callbacks enabled > > > > > > > > > > > > > * @config_lock: protects configuration change reporting > > > > > > > > > > > > > * @dev: underlying device. > > > > > > > > > > > > > * @id: the device type identification (used to match it with a driver). > > > > > > > > > > > > > @@ -109,6 +111,8 @@ struct virtio_device { > > > > > > > > > > > > > bool failed; > > > > > > > > > > > > > bool config_enabled; > > > > > > > > > > > > > bool config_change_pending; > > > > > > > > > > > > > + bool irq_soft_check; > > > > > > > > > > > > > + bool irq_soft_enabled; > > > > > > > > > > > > > spinlock_t config_lock; > > > > > > > > > > > > > spinlock_t vqs_list_lock; /* Protects VQs list access */ > > > > > > > > > > > > > struct device dev; > > > > > > > > > > > > > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h > > > > > > > > > > > > > index dafdc7f48c01..9c1b61f2e525 100644 > > > > > > > > > > > > > --- a/include/linux/virtio_config.h > > > > > > > > > > > > > +++ b/include/linux/virtio_config.h > > > > > > > > > > > > > @@ -174,6 +174,24 @@ static inline bool virtio_has_feature(const struct virtio_device *vdev, > > > > > > > > > > > > > return __virtio_test_bit(vdev, fbit); > > > > > > > > > > > > > } > > > > > > > > > > > > > +/* > > > > > > > > > > > > > + * virtio_irq_soft_enabled: whether we can execute callbacks > > > > > > > > > > > > > + * @vdev: the device > > > > > > > > > > > > > + */ > > > > > > > > > > > > > +static inline bool virtio_irq_soft_enabled(const struct virtio_device *vdev) > > > > > > > > > > > > > +{ > > > > > > > > > > > > > + if (!vdev->irq_soft_check) > > > > > > > > > > > > > + return true; > > > > > > > > > > > > > + > > > > > > > > > > > > > + /* > > > > > > > > > > > > > + * Read irq_soft_enabled before reading other device specific > > > > > > > > > > > > > + * data. Paried with smp_store_relase() in > > > > > > > > > > > > paired > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Will fix. > > > > > > > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > + * virtio_device_ready() and WRITE_ONCE()/synchronize_rcu() in > > > > > > > > > > > > > + * virtio_reset_device(). > > > > > > > > > > > > > + */ > > > > > > > > > > > > > + return smp_load_acquire(&vdev->irq_soft_enabled); > > > > > > > > > > > > > +} > > > > > > > > > > > > > + > > > > > > > > > > > > > /** > > > > > > > > > > > > > * virtio_has_dma_quirk - determine whether this device has the DMA quirk > > > > > > > > > > > > > * @vdev: the device > > > > > > > > > > > > > @@ -236,6 +254,13 @@ void virtio_device_ready(struct virtio_device *dev) > > > > > > > > > > > > > if (dev->config->enable_cbs) > > > > > > > > > > > > > dev->config->enable_cbs(dev); > > > > > > > > > > > > > + /* > > > > > > > > > > > > > + * Commit the driver setup before enabling the virtqueue > > > > > > > > > > > > > + * callbacks. Paried with smp_load_acuqire() in > > > > > > > > > > > > > + * virtio_irq_soft_enabled() > > > > > > > > > > > > > + */ > > > > > > > > > > > > > + smp_store_release(&dev->irq_soft_enabled, true); > > > > > > > > > > > > > + > > > > > > > > > > > > > BUG_ON(status & VIRTIO_CONFIG_S_DRIVER_OK); > > > > > > > > > > > > > dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK); > > > > > > > > > > > > > } > > > > > > > > > > > > > -- > > > > > > > > > > > > > 2.25.1 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from smtp2.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D7A52C433EF for ; Tue, 29 Mar 2022 14:09:11 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp2.osuosl.org (Postfix) with ESMTP id 826C740B39; 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Tsirkin" To: Jason Wang Subject: Re: Message-ID: <20220329100111-mutt-send-email-mst@kernel.org> References: <20220325050947-mutt-send-email-mst@kernel.org> <20220325060659-mutt-send-email-mst@kernel.org> <20220328015757-mutt-send-email-mst@kernel.org> <20220328062452-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: "Paul E. McKenney" , Peter Zijlstra , Marc Zyngier , Keir Fraser , linux-kernel , virtualization , Thomas Gleixner X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Tue, Mar 29, 2022 at 03:12:14PM +0800, Jason Wang wrote: > > > > > > And requesting irq commits all memory otherwise all drivers would be > > > > > > broken, > > > > > > > > > > So I think we might talk different issues: > > > > > > > > > > 1) Whether request_irq() commits the previous setups, I think the > > > > > answer is yes, since the spin_unlock of desc->lock (release) can > > > > > guarantee this though there seems no documentation around > > > > > request_irq() to say this. > > > > > > > > > > And I can see at least drivers/video/fbdev/omap2/omapfb/dss/dispc.c is > > > > > using smp_wmb() before the request_irq(). > > > > > > > > > > And even if write is ordered we still need read to be ordered to be > > > > > paired with that. > > > > IMO it synchronizes with the CPU to which irq is > > delivered. Otherwise basically all drivers would be broken, > > wouldn't they be? > > I guess it's because most of the drivers don't care much about the > buggy/malicious device. And most of the devices may require an extra > step to enable device IRQ after request_irq(). Or it's the charge of > the driver to do the synchronization. It is true that the use-case of malicious devices is somewhat boutique. But I think most drivers do want to have their hotplug routines to be robust, yes. > > I don't know whether it's correct on all platforms, but if not > > we need to fix request_irq. > > > > > > > > > > > > > if it doesn't it just needs to be fixed, not worked around in > > > > > > virtio. > > > > > > > > > > 2) virtio drivers might do a lot of setups between request_irq() and > > > > > virtio_device_ready(): > > > > > > > > > > request_irq() > > > > > driver specific setups > > > > > virtio_device_ready() > > > > > > > > > > CPU 0 probe) request_irq() > > > > > CPU 1 IRQ handler) read the uninitialized variable > > > > > CPU 0 probe) driver specific setups > > > > > CPU 0 probe) smp_store_release(intr_soft_enabled, true), commit the setups > > > > > CPU 1 IRQ handler) read irq_soft_enable as true > > > > > CPU 1 IRQ handler) use the uninitialized variable > > > > > > > > > > Thanks > > > > > > > > > > > > As I said, virtio_device_ready needs to do synchronize_irq. > > > > That will guarantee all setup is visible to the specific IRQ, > > > > > > Only the interrupt after synchronize_irq() returns. > > > > Anything else is a buggy device though. > > Yes, but the goal of this patch is to prevent the possible attack from > buggy(malicious) devices. Right. However if a driver of a *buggy* device somehow sees driver_ok = false even though it's actually initialized, that is not a deal breaker as that does not open us up to an attack. > > > > > >this > > > > is what it's point is. > > > > > > What happens if an interrupt is raised in the middle like: > > > > > > smp_store_release(dev->irq_soft_enabled, true) > > > IRQ handler > > > synchornize_irq() > > > > > > If we don't enforce a reading order, the IRQ handler may still see the > > > uninitialized variable. > > > > > > Thanks > > > > IMHO variables should be initialized before request_irq > > to a value meaning "not a valid interrupt". > > Specifically driver_ok = false. > > Handler in the scenario you describe will then see !driver_ok > > and exit immediately. > > So just to make sure we're on the same page. > > 1) virtio_reset_device() will set the driver_ok to false; > 2) virtio_device_ready() will set the driver_ok to true > > So for virtio drivers, it often did: > > 1) virtio_reset_device() > 2) find_vqs() which will call request_irq() > 3) other driver specific setups > 4) virtio_device_ready() > > In virtio_device_ready(), the patch perform the following currently: > > smp_store_release(driver_ok, true); > set_status(DRIVER_OK); > > Per your suggestion, to add synchronize_irq() after > smp_store_release() so we had > > smp_store_release(driver_ok, true); > synchornize_irq() > set_status(DRIVER_OK) > > Suppose there's a interrupt raised before the synchronize_irq(), if we do: > > if (READ_ONCE(driver_ok)) { > vq->callback() > } > > It will see the driver_ok as true but how can we make sure > vq->callback sees the driver specific setups (3) above? > > And an example is virtio_scsi(): > > virtio_reset_device() > virtscsi_probe() > virtscsi_init() > virtio_find_vqs() > ... > virtscsi_init_vq(&vscsi->event_vq, vqs[1]) > .... > virtio_device_ready() > > In virtscsi_event_done(): > > virtscsi_event_done(): > virtscsi_vq_done(vscsi, &vscsi->event_vq, ...); > > We need to make sure the even_done reads driver_ok before read vscsi->event_vq. > > Thanks See response by Thomas. A simple if (!dev->driver_ok) should be enough, it's all under a lock. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > We use smp_store_relase() > > > > > > > > > to make sure the driver commits the setup before enabling the irq. It > > > > > > > > > means the read needs to be ordered as well in vring_interrupt(). > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Although I couldn't find anything about this in memory-barriers.txt > > > > > > > > > > which surprises me. > > > > > > > > > > > > > > > > > > > > CC Paul to help make sure I'm right. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > To avoid breaking legacy device which can send IRQ before DRIVER_OK, a > > > > > > > > > > > > > module parameter is introduced to enable the hardening so function > > > > > > > > > > > > > hardening is disabled by default. > > > > > > > > > > > > Which devices are these? How come they send an interrupt before there > > > > > > > > > > > > are any buffers in any queues? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I copied this from the commit log for 22b7050a024d7 > > > > > > > > > > > > > > > > > > > > > > " > > > > > > > > > > > > > > > > > > > > > > This change will also benefit old hypervisors (before 2009) > > > > > > > > > > > that send interrupts without checking DRIVER_OK: previously, > > > > > > > > > > > the callback could race with driver-specific initialization. > > > > > > > > > > > " > > > > > > > > > > > > > > > > > > > > > > If this is only for config interrupt, I can remove the above log. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > This is only for config interrupt. > > > > > > > > > > > > > > > > > > Ok. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Note that the hardening is only done for vring interrupt since the > > > > > > > > > > > > > config interrupt hardening is already done in commit 22b7050a024d7 > > > > > > > > > > > > > ("virtio: defer config changed notifications"). But the method that is > > > > > > > > > > > > > used by config interrupt can't be reused by the vring interrupt > > > > > > > > > > > > > handler because it uses spinlock to do the synchronization which is > > > > > > > > > > > > > expensive. > > > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Jason Wang > > > > > > > > > > > > > > > > > > > > > > > > > --- > > > > > > > > > > > > > drivers/virtio/virtio.c | 19 +++++++++++++++++++ > > > > > > > > > > > > > drivers/virtio/virtio_ring.c | 9 ++++++++- > > > > > > > > > > > > > include/linux/virtio.h | 4 ++++ > > > > > > > > > > > > > include/linux/virtio_config.h | 25 +++++++++++++++++++++++++ > > > > > > > > > > > > > 4 files changed, 56 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c > > > > > > > > > > > > > index 8dde44ea044a..85e331efa9cc 100644 > > > > > > > > > > > > > --- a/drivers/virtio/virtio.c > > > > > > > > > > > > > +++ b/drivers/virtio/virtio.c > > > > > > > > > > > > > @@ -7,6 +7,12 @@ > > > > > > > > > > > > > #include > > > > > > > > > > > > > #include > > > > > > > > > > > > > +static bool irq_hardening = false; > > > > > > > > > > > > > + > > > > > > > > > > > > > +module_param(irq_hardening, bool, 0444); > > > > > > > > > > > > > +MODULE_PARM_DESC(irq_hardening, > > > > > > > > > > > > > + "Disalbe IRQ software processing when it is not expected"); > > > > > > > > > > > > > + > > > > > > > > > > > > > /* Unique numbering for virtio devices. */ > > > > > > > > > > > > > static DEFINE_IDA(virtio_index_ida); > > > > > > > > > > > > > @@ -220,6 +226,15 @@ static int virtio_features_ok(struct virtio_device *dev) > > > > > > > > > > > > > * */ > > > > > > > > > > > > > void virtio_reset_device(struct virtio_device *dev) > > > > > > > > > > > > > { > > > > > > > > > > > > > + /* > > > > > > > > > > > > > + * The below synchronize_rcu() guarantees that any > > > > > > > > > > > > > + * interrupt for this line arriving after > > > > > > > > > > > > > + * synchronize_rcu() has completed is guaranteed to see > > > > > > > > > > > > > + * irq_soft_enabled == false. > > > > > > > > > > > > News to me I did not know synchronize_rcu has anything to do > > > > > > > > > > > > with interrupts. Did not you intend to use synchronize_irq? > > > > > > > > > > > > I am not even 100% sure synchronize_rcu is by design a memory barrier > > > > > > > > > > > > though it's most likely is ... > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > According to the comment above tree RCU version of synchronize_rcu(): > > > > > > > > > > > > > > > > > > > > > > """ > > > > > > > > > > > > > > > > > > > > > > * RCU read-side critical sections are delimited by rcu_read_lock() > > > > > > > > > > > * and rcu_read_unlock(), and may be nested. In addition, but only in > > > > > > > > > > > * v5.0 and later, regions of code across which interrupts, preemption, > > > > > > > > > > > * or softirqs have been disabled also serve as RCU read-side critical > > > > > > > > > > > * sections. This includes hardware interrupt handlers, softirq handlers, > > > > > > > > > > > * and NMI handlers. > > > > > > > > > > > """ > > > > > > > > > > > > > > > > > > > > > > So interrupt handlers are treated as read-side critical sections. > > > > > > > > > > > > > > > > > > > > > > And it has the comment for explain the barrier: > > > > > > > > > > > > > > > > > > > > > > """ > > > > > > > > > > > > > > > > > > > > > > * Note that this guarantee implies further memory-ordering guarantees. > > > > > > > > > > > * On systems with more than one CPU, when synchronize_rcu() returns, > > > > > > > > > > > * each CPU is guaranteed to have executed a full memory barrier since > > > > > > > > > > > * the end of its last RCU read-side critical section whose beginning > > > > > > > > > > > * preceded the call to synchronize_rcu(). In addition, each CPU having > > > > > > > > > > > """ > > > > > > > > > > > > > > > > > > > > > > So on SMP it provides a full barrier. And for UP/tiny RCU we don't need the > > > > > > > > > > > barrier, if the interrupt come after WRITE_ONCE() it will see the > > > > > > > > > > > irq_soft_enabled as false. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > You are right. So then > > > > > > > > > > 1. I do not think we need load_acquire - why is it needed? Just > > > > > > > > > > READ_ONCE should do. > > > > > > > > > > > > > > > > > > See above. > > > > > > > > > > > > > > > > > > > 2. isn't synchronize_irq also doing the same thing? > > > > > > > > > > > > > > > > > > > > > > > > > > > Yes, but it requires a config ops since the IRQ knowledge is transport specific. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > + */ > > > > > > > > > > > > > + WRITE_ONCE(dev->irq_soft_enabled, false); > > > > > > > > > > > > > + synchronize_rcu(); > > > > > > > > > > > > > + > > > > > > > > > > > > > dev->config->reset(dev); > > > > > > > > > > > > > } > > > > > > > > > > > > > EXPORT_SYMBOL_GPL(virtio_reset_device); > > > > > > > > > > > > Please add comment explaining where it will be enabled. > > > > > > > > > > > > Also, we *really* don't need to synch if it was already disabled, > > > > > > > > > > > > let's not add useless overhead to the boot sequence. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Ok. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > @@ -427,6 +442,10 @@ int register_virtio_device(struct virtio_device *dev) > > > > > > > > > > > > > spin_lock_init(&dev->config_lock); > > > > > > > > > > > > > dev->config_enabled = false; > > > > > > > > > > > > > dev->config_change_pending = false; > > > > > > > > > > > > > + dev->irq_soft_check = irq_hardening; > > > > > > > > > > > > > + > > > > > > > > > > > > > + if (dev->irq_soft_check) > > > > > > > > > > > > > + dev_info(&dev->dev, "IRQ hardening is enabled\n"); > > > > > > > > > > > > > /* We always start by resetting the device, in case a previous > > > > > > > > > > > > > * driver messed it up. This also tests that code path a little. */ > > > > > > > > > > > > one of the points of hardening is it's also helpful for buggy > > > > > > > > > > > > devices. this flag defeats the purpose. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Do you mean: > > > > > > > > > > > > > > > > > > > > > > 1) we need something like config_enable? This seems not easy to be > > > > > > > > > > > implemented without obvious overhead, mainly the synchronize with the > > > > > > > > > > > interrupt handlers > > > > > > > > > > > > > > > > > > > > But synchronize is only on tear-down path. That is not critical for any > > > > > > > > > > users at the moment, even less than probe. > > > > > > > > > > > > > > > > > > I meant if we have vq->irq_pending, we need to call vring_interrupt() > > > > > > > > > in the virtio_device_ready() and synchronize the IRQ handlers with > > > > > > > > > spinlock or others. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 2) enable this by default, so I don't object, but this may have some risk > > > > > > > > > > > for old hypervisors > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The risk if there's a driver adding buffers without setting DRIVER_OK. > > > > > > > > > > > > > > > > > > Probably not, we have devices that accept random inputs from outside, > > > > > > > > > net, console, input etc. I've done a round of audits of the Qemu > > > > > > > > > codes. They look all fine since day0. > > > > > > > > > > > > > > > > > > > So with this approach, how about we rename the flag "driver_ok"? > > > > > > > > > > And then add_buf can actually test it and BUG_ON if not there (at least > > > > > > > > > > in the debug build). > > > > > > > > > > > > > > > > > > This looks like a hardening of the driver in the core instead of the > > > > > > > > > device. I think it can be done but in a separate series. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > And going down from there, how about we cache status in the > > > > > > > > > > device? Then we don't need to keep re-reading it every time, > > > > > > > > > > speeding boot up a tiny bit. > > > > > > > > > > > > > > > > > > I don't fully understand here, actually spec requires status to be > > > > > > > > > read back for validation in many cases. > > > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > > > > > > > > > > > > index 962f1477b1fa..0170f8c784d8 100644 > > > > > > > > > > > > > --- a/drivers/virtio/virtio_ring.c > > > > > > > > > > > > > +++ b/drivers/virtio/virtio_ring.c > > > > > > > > > > > > > @@ -2144,10 +2144,17 @@ static inline bool more_used(const struct vring_virtqueue *vq) > > > > > > > > > > > > > return vq->packed_ring ? more_used_packed(vq) : more_used_split(vq); > > > > > > > > > > > > > } > > > > > > > > > > > > > -irqreturn_t vring_interrupt(int irq, void *_vq) > > > > > > > > > > > > > +irqreturn_t vring_interrupt(int irq, void *v) > > > > > > > > > > > > > { > > > > > > > > > > > > > + struct virtqueue *_vq = v; > > > > > > > > > > > > > + struct virtio_device *vdev = _vq->vdev; > > > > > > > > > > > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > > > > > > > > + if (!virtio_irq_soft_enabled(vdev)) { > > > > > > > > > > > > > + dev_warn_once(&vdev->dev, "virtio vring IRQ raised before DRIVER_OK"); > > > > > > > > > > > > > + return IRQ_NONE; > > > > > > > > > > > > > + } > > > > > > > > > > > > > + > > > > > > > > > > > > > if (!more_used(vq)) { > > > > > > > > > > > > > pr_debug("virtqueue interrupt with no work for %p\n", vq); > > > > > > > > > > > > > return IRQ_NONE; > > > > > > > > > > > > > diff --git a/include/linux/virtio.h b/include/linux/virtio.h > > > > > > > > > > > > > index 5464f398912a..957d6ad604ac 100644 > > > > > > > > > > > > > --- a/include/linux/virtio.h > > > > > > > > > > > > > +++ b/include/linux/virtio.h > > > > > > > > > > > > > @@ -95,6 +95,8 @@ dma_addr_t virtqueue_get_used_addr(struct virtqueue *vq); > > > > > > > > > > > > > * @failed: saved value for VIRTIO_CONFIG_S_FAILED bit (for restore) > > > > > > > > > > > > > * @config_enabled: configuration change reporting enabled > > > > > > > > > > > > > * @config_change_pending: configuration change reported while disabled > > > > > > > > > > > > > + * @irq_soft_check: whether or not to check @irq_soft_enabled > > > > > > > > > > > > > + * @irq_soft_enabled: callbacks enabled > > > > > > > > > > > > > * @config_lock: protects configuration change reporting > > > > > > > > > > > > > * @dev: underlying device. > > > > > > > > > > > > > * @id: the device type identification (used to match it with a driver). > > > > > > > > > > > > > @@ -109,6 +111,8 @@ struct virtio_device { > > > > > > > > > > > > > bool failed; > > > > > > > > > > > > > bool config_enabled; > > > > > > > > > > > > > bool config_change_pending; > > > > > > > > > > > > > + bool irq_soft_check; > > > > > > > > > > > > > + bool irq_soft_enabled; > > > > > > > > > > > > > spinlock_t config_lock; > > > > > > > > > > > > > spinlock_t vqs_list_lock; /* Protects VQs list access */ > > > > > > > > > > > > > struct device dev; > > > > > > > > > > > > > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h > > > > > > > > > > > > > index dafdc7f48c01..9c1b61f2e525 100644 > > > > > > > > > > > > > --- a/include/linux/virtio_config.h > > > > > > > > > > > > > +++ b/include/linux/virtio_config.h > > > > > > > > > > > > > @@ -174,6 +174,24 @@ static inline bool virtio_has_feature(const struct virtio_device *vdev, > > > > > > > > > > > > > return __virtio_test_bit(vdev, fbit); > > > > > > > > > > > > > } > > > > > > > > > > > > > +/* > > > > > > > > > > > > > + * virtio_irq_soft_enabled: whether we can execute callbacks > > > > > > > > > > > > > + * @vdev: the device > > > > > > > > > > > > > + */ > > > > > > > > > > > > > +static inline bool virtio_irq_soft_enabled(const struct virtio_device *vdev) > > > > > > > > > > > > > +{ > > > > > > > > > > > > > + if (!vdev->irq_soft_check) > > > > > > > > > > > > > + return true; > > > > > > > > > > > > > + > > > > > > > > > > > > > + /* > > > > > > > > > > > > > + * Read irq_soft_enabled before reading other device specific > > > > > > > > > > > > > + * data. Paried with smp_store_relase() in > > > > > > > > > > > > paired > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Will fix. > > > > > > > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > + * virtio_device_ready() and WRITE_ONCE()/synchronize_rcu() in > > > > > > > > > > > > > + * virtio_reset_device(). > > > > > > > > > > > > > + */ > > > > > > > > > > > > > + return smp_load_acquire(&vdev->irq_soft_enabled); > > > > > > > > > > > > > +} > > > > > > > > > > > > > + > > > > > > > > > > > > > /** > > > > > > > > > > > > > * virtio_has_dma_quirk - determine whether this device has the DMA quirk > > > > > > > > > > > > > * @vdev: the device > > > > > > > > > > > > > @@ -236,6 +254,13 @@ void virtio_device_ready(struct virtio_device *dev) > > > > > > > > > > > > > if (dev->config->enable_cbs) > > > > > > > > > > > > > dev->config->enable_cbs(dev); > > > > > > > > > > > > > + /* > > > > > > > > > > > > > + * Commit the driver setup before enabling the virtqueue > > > > > > > > > > > > > + * callbacks. Paried with smp_load_acuqire() in > > > > > > > > > > > > > + * virtio_irq_soft_enabled() > > > > > > > > > > > > > + */ > > > > > > > > > > > > > + smp_store_release(&dev->irq_soft_enabled, true); > > > > > > > > > > > > > + > > > > > > > > > > > > > BUG_ON(status & VIRTIO_CONFIG_S_DRIVER_OK); > > > > > > > > > > > > > dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK); > > > > > > > > > > > > > } > > > > > > > > > > > > > -- > > > > > > > > > > > > > 2.25.1 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization