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Tsirkin" To: Jason Wang Subject: Re: [PATCH V2 07/12] virtio-pci: harden INTX interrupts Message-ID: <20211014052435-mutt-send-email-mst@kernel.org> References: <20211012065227.9953-1-jasowang@redhat.com> <20211012065227.9953-8-jasowang@redhat.com> <20211013053627-mutt-send-email-mst@kernel.org> <20211014014551-mutt-send-email-mst@kernel.org> <20211014022438-mutt-send-email-mst@kernel.org> <20211014025815-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" , "kaplan, david" , Konrad Rzeszutek Wilk , Peter Zijlstra , Boqun Feng , "Hetzelt, Felicitas" , 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 Thu, Oct 14, 2021 at 03:12:54PM +0800, Jason Wang wrote: > On Thu, Oct 14, 2021 at 3:04 PM Michael S. Tsirkin wrote: > > > > On Thu, Oct 14, 2021 at 02:32:19PM +0800, Jason Wang wrote: > > > On Thu, Oct 14, 2021 at 2:26 PM Michael S. Tsirkin wrote: > > > > > > > > On Thu, Oct 14, 2021 at 02:20:17PM +0800, Jason Wang wrote: > > > > > On Thu, Oct 14, 2021 at 1:50 PM Michael S. Tsirkin wrote: > > > > > > > > > > > > On Thu, Oct 14, 2021 at 10:35:48AM +0800, Jason Wang wrote: > > > > > > > On Wed, Oct 13, 2021 at 5:42 PM Michael S. Tsirkin wrote: > > > > > > > > > > > > > > > > On Tue, Oct 12, 2021 at 02:52:22PM +0800, Jason Wang wrote: > > > > > > > > > This patch tries to make sure the virtio interrupt handler for INTX > > > > > > > > > won't be called after a reset and before virtio_device_ready(). We > > > > > > > > > can't use IRQF_NO_AUTOEN since we're using shared interrupt > > > > > > > > > (IRQF_SHARED). So this patch tracks the INTX enabling status in a new > > > > > > > > > intx_soft_enabled variable and toggle it during in > > > > > > > > > vp_disable/enable_vectors(). The INTX interrupt handler will check > > > > > > > > > intx_soft_enabled before processing the actual interrupt. > > > > > > > > > > > > > > > > > > Cc: Boqun Feng > > > > > > > > > Cc: Thomas Gleixner > > > > > > > > > Cc: Peter Zijlstra > > > > > > > > > Cc: Paul E. McKenney > > > > > > > > > Signed-off-by: Jason Wang > > > > > > > > > --- > > > > > > > > > drivers/virtio/virtio_pci_common.c | 24 ++++++++++++++++++++++-- > > > > > > > > > drivers/virtio/virtio_pci_common.h | 1 + > > > > > > > > > 2 files changed, 23 insertions(+), 2 deletions(-) > > > > > > > > > > > > > > > > > > diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c > > > > > > > > > index 0b9523e6dd39..5ae6a2a4eb77 100644 > > > > > > > > > --- a/drivers/virtio/virtio_pci_common.c > > > > > > > > > +++ b/drivers/virtio/virtio_pci_common.c > > > > > > > > > @@ -30,8 +30,16 @@ void vp_disable_vectors(struct virtio_device *vdev) > > > > > > > > > struct virtio_pci_device *vp_dev = to_vp_device(vdev); > > > > > > > > > int i; > > > > > > > > > > > > > > > > > > - if (vp_dev->intx_enabled) > > > > > > > > > + if (vp_dev->intx_enabled) { > > > > > > > > > + /* > > > > > > > > > + * The below synchronize() guarantees that any > > > > > > > > > + * interrupt for this line arriving after > > > > > > > > > + * synchronize_irq() has completed is guaranteed to see > > > > > > > > > + * intx_soft_enabled == false. > > > > > > > > > + */ > > > > > > > > > + WRITE_ONCE(vp_dev->intx_soft_enabled, false); > > > > > > > > > synchronize_irq(vp_dev->pci_dev->irq); > > > > > > > > > + } > > > > > > > > > > > > > > > > > > for (i = 0; i < vp_dev->msix_vectors; ++i) > > > > > > > > > disable_irq(pci_irq_vector(vp_dev->pci_dev, i)); > > > > > > > > > @@ -43,8 +51,16 @@ void vp_enable_vectors(struct virtio_device *vdev) > > > > > > > > > struct virtio_pci_device *vp_dev = to_vp_device(vdev); > > > > > > > > > int i; > > > > > > > > > > > > > > > > > > - if (vp_dev->intx_enabled) > > > > > > > > > + if (vp_dev->intx_enabled) { > > > > > > > > > + disable_irq(vp_dev->pci_dev->irq); > > > > > > > > > + /* > > > > > > > > > + * The above disable_irq() provides TSO ordering and > > > > > > > > > + * as such promotes the below store to store-release. > > > > > > > > > + */ > > > > > > > > > + WRITE_ONCE(vp_dev->intx_soft_enabled, true); > > > > > > > > > + enable_irq(vp_dev->pci_dev->irq); > > > > > > > > > return; > > > > > > > > > + } > > > > > > > > > > > > > > > > > > for (i = 0; i < vp_dev->msix_vectors; ++i) > > > > > > > > > enable_irq(pci_irq_vector(vp_dev->pci_dev, i)); > > > > > > > > > @@ -97,6 +113,10 @@ static irqreturn_t vp_interrupt(int irq, void *opaque) > > > > > > > > > struct virtio_pci_device *vp_dev = opaque; > > > > > > > > > u8 isr; > > > > > > > > > > > > > > > > > > + /* read intx_soft_enabled before read others */ > > > > > > > > > + if (!smp_load_acquire(&vp_dev->intx_soft_enabled)) > > > > > > > > > + return IRQ_NONE; > > > > > > > > > + > > > > > > > > > /* reading the ISR has the effect of also clearing it so it's very > > > > > > > > > * important to save off the value. */ > > > > > > > > > isr = ioread8(vp_dev->isr); > > > > > > > > > > > > > > > > I don't see why we need this ordering guarantee here. > > > > > > > > > > > > > > > > synchronize_irq above makes sure no interrupt handler > > > > > > > > is in progress. > > > > > > > > > > > > > > Yes. > > > > > > > > > > > > > > > the handler itself thus does not need > > > > > > > > any specific order, it is ok if intx_soft_enabled is read > > > > > > > > after, not before the rest of it. > > > > > > > > > > > > > > But the interrupt could be raised after synchronize_irq() which may > > > > > > > see a false of the intx_soft_enabled. > > > > > > > > > > > > You mean a "true" value right? false is what we are writing there. > > > > > > > > > > I meant that we want to not go for stuff like vq->callback after the > > > > > synchronize_irq() after setting intx_soft_enabled to false. Otherwise > > > > > we may get unexpected results like use after free. Host can craft ISR > > > > > in this case. > > > > > > > > > > > > Are you sure it can happen? I think that synchronize_irq makes the value > > > > > > visible on all CPUs running the irq. > > > > > > > > > > Yes, so the false is visible by vp_interrupt(), we can't do the other > > > > > task before we check intx_soft_enabled. > > > > > > > > But the order does not matter. synchronize_irq will make sure > > > > everything is visible. > > > > > > Not the thing that happens after synchronize_irq(). > > > > > > E.g for remove_vq_common(): > > > > > > static void remove_vq_common(struct virtnet_info *vi) > > > { > > > vi->vdev->config->reset(vi->vdev); > > > > > > /* Free unused buffers in both send and recv, if any. */ > > > free_unused_bufs(vi); > > > > > > free_receive_bufs(vi); > > > > > > free_receive_page_frags(vi); > > > > > > virtnet_del_vqs(vi); > > > } > > > > > > The interrupt could be raised by the device after .reset(). > > > > > > Thanks > > > > That's why your patches set intx_soft_enabled to false within reset. > > Then you sync so all other CPUs see the false value. > > Then it's ok to proceed with reset. > > What does the interrupt handler *do* with the value > > does not matter as long as it sees that it is false. > > I'm not sure I get here, if we allow the interrupt handler to access > the vq before checking intx_soft_enabled, won't there be a > use-after-free? It's a speculative access, not an architectural one. > > > > OTOH if you are really worried about spectre type speculative attacks, > > that is a different matter, and would force us to stick expensive > > barriers around hardware accessible buffers just like we have in > > copy_XXX_user. I am not sure this is in scope for TDX, and > > certainly out of scope for regular driver ardening. > > If yes worth hiding that behind a kernel option. > > Right. > > Thanks > > > > > > > > > > > > > > > > > > > > > > In this case we still need the > > > > > > > make sure intx_soft_enbled to be read first instead of allowing other > > > > > > > operations to be done first, otherwise the intx_soft_enabled is > > > > > > > meaningless. > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > If intx_soft_enbled were not visible after synchronize_irq then > > > > > > it does not matter in which order we read it wrt other values, > > > > > > it still wouldn't work right. > > > > > > > > > > Yes. > > > > > > > > > > Thanks > > > > > > > > > > > > We are agreed then? No need for a barrier here, READ_ONCE is enough? > > > > > > > > > > > > > > > > > > > > > > > > > > Just READ_ONCE should be enough, and we can drop the comment. > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h > > > > > > > > > index a235ce9ff6a5..3c06e0f92ee4 100644 > > > > > > > > > --- a/drivers/virtio/virtio_pci_common.h > > > > > > > > > +++ b/drivers/virtio/virtio_pci_common.h > > > > > > > > > @@ -64,6 +64,7 @@ struct virtio_pci_device { > > > > > > > > > /* MSI-X support */ > > > > > > > > > int msix_enabled; > > > > > > > > > int intx_enabled; > > > > > > > > > + bool intx_soft_enabled; > > > > > > > > > cpumask_var_t *msix_affinity_masks; > > > > > > > > > /* Name strings for interrupts. This size should be enough, > > > > > > > > > * and I'm too lazy to allocate each name separately. */ > > > > > > > > > -- > > > > > > > > > 2.25.1 > > > > > > > > > > > > > > > > > > > > _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization