Virtualization - Nov 2014 - [PATCH V3 1/2] virtio: introduce methods of sanitizing device features

Buggy host may advertised buggy host features (a usual case is that host
advertise a feature whose dependencies were missed). In this case, driver
should detect and disable the buggy features by itself.

This patch introduces driver specific sanitize_features() method which is
called just before features finalizing to detect and disable buggy features
advertised by host.

Virtio-net will be the first user.

Cc: Rusty Russell <rusty at rustcorp.com.au>
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
Cc: Wanlong Gao <gaowanlong at cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
Changes from V2:
- fix typo
- rename fix_features to sanitize_features
---
 drivers/virtio/virtio.c       |  4 ++++
 include/linux/virtio.h        |  1 +
 include/linux/virtio_config.h | 12 ++++++++++++
 3 files changed, 17 insertions(+)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index df598dd..6a86b4f 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -181,6 +181,10 @@ static int virtio_dev_probe(struct device *_d)
 		if (device_features & (1 << i))
 			set_bit(i, dev->features);
 
+	/* Sanitize buggy features advertised by host */
+	if (drv->sanitize_features)
+		drv->sanitize_features(dev);
+
 	dev->config->finalize_features(dev);
 
 	err = drv->probe(dev);
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 65261a7..5aed283 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -142,6 +142,7 @@ struct virtio_driver {
 	void (*scan)(struct virtio_device *dev);
 	void (*remove)(struct virtio_device *dev);
 	void (*config_changed)(struct virtio_device *dev);
+	void (*sanitize_features)(struct virtio_device *dev);
 #ifdef CONFIG_PM
 	int (*freeze)(struct virtio_device *dev);
 	int (*restore)(struct virtio_device *dev);
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 7f4ef66..7bd89ea 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -96,6 +96,18 @@ static inline bool virtio_has_feature(const struct
virtio_device *vdev,
 	return test_bit(fbit, vdev->features);
 }
 
+static inline void virtio_disable_feature(struct virtio_device *vdev,
+                                          unsigned int fbit)
+{
+	BUG_ON(fbit >= VIRTIO_TRANSPORT_F_START);
+	BUG_ON(vdev->config->get_status(vdev) &
+	       ~(VIRTIO_CONFIG_S_ACKNOWLEDGE | VIRTIO_CONFIG_S_DRIVER));
+
+	virtio_check_driver_offered_feature(vdev, fbit);
+
+	clear_bit(fbit, vdev->features);
+}
+
 static inline
 struct virtqueue *virtio_find_single_vq(struct virtio_device *vdev,
 					vq_callback_t *c, const char *n)
-- 
1.9.1

This patch tries to detect the possible buggy features advertised by host
and sanitize them. One example is booting virtio-net with only ctrl_vq
disabled, qemu may still advertise many features which depends on it. This
will trigger several BUG()s in virtnet_send_command().

This patch utilizes the sanitize_features() method, and disables all
features that depends on ctrl_vq if it was not advertised.

This fixes the crash when booting with ctrl_vq=off using qemu.

Cc: Rusty Russell <rusty at rustcorp.com.au>
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
Cc: Wanlong Gao <gaowanlong at cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
Changes from V1:
- fix the cut-and-paste error
Changes from V2:
- loop through an array of feature bits
- switch to use dev_warn()
---
 drivers/net/virtio_net.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ec2a8b4..6fadd8c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1948,6 +1948,31 @@ static int virtnet_restore(struct virtio_device *vdev)
 }
 #endif
 
+static void virtnet_sanitize_features(struct virtio_device *dev)
+{
+	unsigned int features_for_ctrl_vq[] = {
+		VIRTIO_NET_F_CTRL_RX,
+		VIRTIO_NET_F_CTRL_VLAN,
+		VIRTIO_NET_F_GUEST_ANNOUNCE,
+		VIRTIO_NET_F_MQ,
+		VIRTIO_NET_F_CTRL_MAC_ADDR
+	};
+	int i;
+
+	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
+		for (i = 0; i < ARRAY_SIZE(features_for_ctrl_vq); i++) {
+			unsigned int f = features_for_ctrl_vq[i];
+			if (virtio_has_feature(dev, f)) {
+				virtio_disable_feature(dev, f);
+				dev_warn(&dev->dev,
+					 "buggy hyperviser: disable feature "
+					 "0x%x since VIRTIO_NET_F_CTRL_VQ was "
+					 "not advertised.\n", f);
+			}
+		}
+	}
+}
+
 static struct virtio_device_id id_table[] = {
 	{ VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
 	{ 0 },
@@ -1975,6 +2000,7 @@ static struct virtio_driver virtio_net_driver = {
 	.probe =	virtnet_probe,
 	.remove =	virtnet_remove,
 	.config_changed = virtnet_config_changed,
+	.sanitize_features = virtnet_sanitize_features,
 #ifdef CONFIG_PM_SLEEP
 	.freeze =	virtnet_freeze,
 	.restore =	virtnet_restore,
-- 
1.9.1

On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang
wrote:
> Buggy host may advertised buggy host features (a usual case is that host
> advertise a feature whose dependencies were missed). In this case, driver
> should detect and disable the buggy features by itself.
> 
> This patch introduces driver specific sanitize_features() method which is
> called just before features finalizing to detect and disable buggy features
> advertised by host.
> 
> Virtio-net will be the first user.
> 
> Cc: Rusty Russell <rusty at rustcorp.com.au>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
> Cc: Wanlong Gao <gaowanlong at cn.fujitsu.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
Hmm this conflicts with virtio 1.0 work: we drop
features as bitmap there.
> ---
> Changes from V2:
> - fix typo
> - rename fix_features to sanitize_features
> ---
>  drivers/virtio/virtio.c       |  4 ++++
>  include/linux/virtio.h        |  1 +
>  include/linux/virtio_config.h | 12 ++++++++++++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index df598dd..6a86b4f 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -181,6 +181,10 @@ static int virtio_dev_probe(struct device *_d)
>  		if (device_features & (1 << i))
>  			set_bit(i, dev->features);
>  
> +	/* Sanitize buggy features advertised by host */
> +	if (drv->sanitize_features)
> +		drv->sanitize_features(dev);
> +
>  	dev->config->finalize_features(dev);
>  
>  	err = drv->probe(dev);
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 65261a7..5aed283 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -142,6 +142,7 @@ struct virtio_driver {
>  	void (*scan)(struct virtio_device *dev);
>  	void (*remove)(struct virtio_device *dev);
>  	void (*config_changed)(struct virtio_device *dev);
> +	void (*sanitize_features)(struct virtio_device *dev);
>  #ifdef CONFIG_PM
>  	int (*freeze)(struct virtio_device *dev);
>  	int (*restore)(struct virtio_device *dev);
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 7f4ef66..7bd89ea 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -96,6 +96,18 @@ static inline bool virtio_has_feature(const struct
virtio_device *vdev,
>  	return test_bit(fbit, vdev->features);
>  }
>  
> +static inline void virtio_disable_feature(struct virtio_device *vdev,
> +                                          unsigned int fbit)
> +{
> +	BUG_ON(fbit >= VIRTIO_TRANSPORT_F_START);
> +	BUG_ON(vdev->config->get_status(vdev) &
> +	       ~(VIRTIO_CONFIG_S_ACKNOWLEDGE | VIRTIO_CONFIG_S_DRIVER));
> +
> +	virtio_check_driver_offered_feature(vdev, fbit);
> +
> +	clear_bit(fbit, vdev->features);
> +}
> +
>  static inline
>  struct virtqueue *virtio_find_single_vq(struct virtio_device *vdev,
>  					vq_callback_t *c, const char *n)
> -- 
> 1.9.1

On Mon, 17 Nov 2014 11:37:01 +0200
"Michael S. Tsirkin" <mst at redhat.com> wrote:
> On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote:
> > Buggy host may advertised buggy host features (a usual case is that
host
> > advertise a feature whose dependencies were missed). In this case,
driver
> > should detect and disable the buggy features by itself.
> > 
> > This patch introduces driver specific sanitize_features() method which
is
> > called just before features finalizing to detect and disable buggy
features
> > advertised by host.
> > 
> > Virtio-net will be the first user.
> > 
> > Cc: Rusty Russell <rusty at rustcorp.com.au>
> > Cc: Michael S. Tsirkin <mst at redhat.com>
> > Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
> > Cc: Wanlong Gao <gaowanlong at cn.fujitsu.com>
> > Signed-off-by: Jason Wang <jasowang at redhat.com>
> 
> Hmm this conflicts with virtio 1.0 work: we drop
> features as bitmap there.
But that's an implementation detail, no? We'll still need a way for the
driver to sanitize features, and I think this interface works just fine.

On Mon, Nov 17, 2014 at 05:17:18PM +0800, Jason Wang
wrote:
> This patch tries to detect the possible buggy features advertised by host
> and sanitize them. One example is booting virtio-net with only ctrl_vq
> disabled, qemu may still advertise many features which depends on it. This
> will trigger several BUG()s in virtnet_send_command().
> 
> This patch utilizes the sanitize_features() method, and disables all
> features that depends on ctrl_vq if it was not advertised.
> 
> This fixes the crash when booting with ctrl_vq=off using qemu.
> 
> Cc: Rusty Russell <rusty at rustcorp.com.au>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
> Cc: Wanlong Gao <gaowanlong at cn.fujitsu.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>

So I'm not sure this is useful.
The spec says:
	The device MUST NOT offer a feature which requires another feature which
	was not offered.
So this is a buggy hypervisor, and I believe we should just fail probe.
This can be done without crashing, and is generally a better
idea that second-guessing what hypervisor wants us to do.





However, assuming that we do want this change:
This can be replaced with a table driven design in virtio core, but
since you chose to open code it, I would drop table below altogether.


Just make it
	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_RX);
		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_VLAN);
		virtio_disable_feature(dev, VIRTIO_NET_F_GUEST_ANNOUNCE);
		virtio_disable_feature(dev, VIRTIO_NET_F_MQ);
		virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_MAC_ADDR);
	}



> ---
> Changes from V1:
> - fix the cut-and-paste error
> Changes from V2:
> - loop through an array of feature bits
> - switch to use dev_warn()
> ---
>  drivers/net/virtio_net.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index ec2a8b4..6fadd8c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1948,6 +1948,31 @@ static int virtnet_restore(struct virtio_device
*vdev)
>  }
>  #endif
>  
> +static void virtnet_sanitize_features(struct virtio_device *dev)
> +{
> +	unsigned int features_for_ctrl_vq[] = {
> +		VIRTIO_NET_F_CTRL_RX,
> +		VIRTIO_NET_F_CTRL_VLAN,
> +		VIRTIO_NET_F_GUEST_ANNOUNCE,
> +		VIRTIO_NET_F_MQ,
> +		VIRTIO_NET_F_CTRL_MAC_ADDR
> +	};
This is not the only dependency: checksums
have dependencies too. See virtio 1.0 spec.


> +	int i;
> +
> +	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
> +		for (i = 0; i < ARRAY_SIZE(features_for_ctrl_vq); i++) {
> +			unsigned int f = features_for_ctrl_vq[i];
> +			if (virtio_has_feature(dev, f)) {
> +				virtio_disable_feature(dev, f);
> +				dev_warn(&dev->dev,
> +					 "buggy hyperviser: disable feature "
> +					 "0x%x since VIRTIO_NET_F_CTRL_VQ was "
> +					 "not advertised.\n", f);
> +			}
> +		}
> +	}
> +}
> +
>  static struct virtio_device_id id_table[] = {
>  	{ VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
>  	{ 0 },
> @@ -1975,6 +2000,7 @@ static struct virtio_driver virtio_net_driver = {
>  	.probe =	virtnet_probe,
>  	.remove =	virtnet_remove,
>  	.config_changed = virtnet_config_changed,
> +	.sanitize_features = virtnet_sanitize_features,
>  #ifdef CONFIG_PM_SLEEP
>  	.freeze =	virtnet_freeze,
>  	.restore =	virtnet_restore,
> -- 
> 1.9.1