Linux Virtualization - Jul 2020 - [PATCH v7 2/2] s390: virtio: PV needs VIRTIO I/O device protection

Hi all,

The goal of the series is to give a chance to the architecture
to validate VIRTIO device features.

in this respin:

1) I kept removed the ack from Jason as I reworked the patch
   @Jason, the nature and goal of the patch did not really changed
           please can I get back your acked-by with these changes?

2) Rewording for warning messages

Regards,
Pierre

Pierre Morel (2):
  virtio: let arch validate VIRTIO features
  s390: virtio: PV needs VIRTIO I/O device protection

 arch/s390/mm/init.c           | 28 ++++++++++++++++++++++++++++
 drivers/virtio/virtio.c       | 19 +++++++++++++++++++
 include/linux/virtio_config.h |  1 +
 3 files changed, 48 insertions(+)

-- 
2.25.1

Changelog

to v7:

- typo in warning message
  (Connie)
to v6:

- rewording warning messages
  (Connie, Halil)

to v5:

- return directly from S390 arch_validate_virtio_features()
  when the guest is not protected.
  (Connie)

- Somme rewording
  (Connie, Michael)

- moved back code from arch/s390/ ...kernel/uv.c to ...mm/init.c
  (Christian)

to v4:

- separate virtio and arch code
  (Pierre)

- moved code from arch/s390/mm/init.c to arch/s390/kernel/uv.c
  (as interpreted from Heiko's comment)

- moved validation inside the arch code
  (Connie)

- moved the call to arch validation before VIRTIO_F_1 test
  (Michael)

to v3:

- add warning
  (Connie, Christian)

- add comment
  (Connie)

- change hook name
  (Halil, Connie)

to v2:

- put the test in virtio_finalize_features()
  (Connie)

- put the test inside VIRTIO core
  (Jason)

- pass a virtio device as parameter
  (Halil)

An architecture may need to validate the VIRTIO devices features
based on architecture specifics.

Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck at redhat.com>
Acked-by: Christian Borntraeger <borntraeger at de.ibm.com>
Acked-by: Halil Pasic <pasic at linux.ibm.com>
---
 drivers/virtio/virtio.c       | 19 +++++++++++++++++++
 include/linux/virtio_config.h |  1 +
 2 files changed, 20 insertions(+)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index a977e32a88f2..c4e14d46a5b6 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -167,6 +167,21 @@ void virtio_add_status(struct virtio_device *dev, unsigned
int status)
 }
 EXPORT_SYMBOL_GPL(virtio_add_status);
 
+/*
+ * arch_validate_virtio_features - provide arch specific hook when finalizing
+ *				   features for VIRTIO device dev
+ * @dev: the VIRTIO device being added
+ *
+ * Permits the platform to handle architecture-specific requirements when
+ * device features are finalized. This is the default implementation.
+ * Architecture implementations can override this.
+ */
+
+int __weak arch_validate_virtio_features(struct virtio_device *dev)
+{
+	return 0;
+}
+
 int virtio_finalize_features(struct virtio_device *dev)
 {
 	int ret = dev->config->finalize_features(dev);
@@ -176,6 +191,10 @@ int virtio_finalize_features(struct virtio_device *dev)
 	if (ret)
 		return ret;
 
+	ret = arch_validate_virtio_features(dev);
+	if (ret)
+		return ret;
+
 	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
 		return 0;
 
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index bb4cc4910750..3f4117adf311 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -459,4 +459,5 @@ static inline void virtio_cwrite64(struct virtio_device
*vdev,
 		_r;							\
 	})
 
+int arch_validate_virtio_features(struct virtio_device *dev);
 #endif /* _LINUX_VIRTIO_CONFIG_H */
-- 
2.25.1

If protected virtualization is active on s390, the virtio queues are
not accessible to the host, unless VIRTIO_F_IOMMU_PLATFORM has been
negotiated. Use the new arch_validate_virtio_features() interface to
fail probe if that's not the case, preventing a host error on access
attempt.

Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck at redhat.com>
Acked-by: Halil Pasic <pasic at linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger at de.ibm.com>
---
 arch/s390/mm/init.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 6dc7c3b60ef6..d39af6554d4f 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -45,6 +45,7 @@
 #include <asm/kasan.h>
 #include <asm/dma-mapping.h>
 #include <asm/uv.h>
+#include <linux/virtio_config.h>
 
 pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
 
@@ -161,6 +162,33 @@ bool force_dma_unencrypted(struct device *dev)
 	return is_prot_virt_guest();
 }
 
+/*
+ * arch_validate_virtio_features
+ * @dev: the VIRTIO device being added
+ *
+ * Return an error if required features are missing on a guest running
+ * with protected virtualization.
+ */
+int arch_validate_virtio_features(struct virtio_device *dev)
+{
+	if (!is_prot_virt_guest())
+		return 0;
+
+	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
+		dev_warn(&dev->dev,
+			 "legacy virtio not supported with protected virtualization\n");
+		return -ENODEV;
+	}
+
+	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
+		dev_warn(&dev->dev,
+			 "support for limited memory access required for protected
virtualization\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
 /* protected virtualization */
 static void pv_init(void)
 {
-- 
2.25.1

On 2020/7/15 ??4:31, Pierre Morel wrote:
> Hi all,
>
> The goal of the series is to give a chance to the architecture
> to validate VIRTIO device features.
>
> in this respin:
>
> 1) I kept removed the ack from Jason as I reworked the patch
>     @Jason, the nature and goal of the patch did not really changed
>             please can I get back your acked-by with these changes?

Yes.

Acked-by: Jason Wang <jasowang at redhat.com>

Thanks

>
> 2) Rewording for warning messages
>
> Regards,
> Pierre
>
> Pierre Morel (2):
>    virtio: let arch validate VIRTIO features
>    s390: virtio: PV needs VIRTIO I/O device protection
>
>   arch/s390/mm/init.c           | 28 ++++++++++++++++++++++++++++
>   drivers/virtio/virtio.c       | 19 +++++++++++++++++++
>   include/linux/virtio_config.h |  1 +
>   3 files changed, 48 insertions(+)
>

On Wed, 15 Jul 2020 10:31:07 +0200
Pierre Morel <pmorel at linux.ibm.com> wrote:
> Hi all,
> 
> The goal of the series is to give a chance to the architecture
> to validate VIRTIO device features.
> 
> in this respin:
> 
> 1) I kept removed the ack from Jason as I reworked the patch
>    @Jason, the nature and goal of the patch did not really changed
>            please can I get back your acked-by with these changes?
> 
> 2) Rewording for warning messages
> 
> Regards,
> Pierre
> 
> Pierre Morel (2):
>   virtio: let arch validate VIRTIO features
>   s390: virtio: PV needs VIRTIO I/O device protection
> 
>  arch/s390/mm/init.c           | 28 ++++++++++++++++++++++++++++
>  drivers/virtio/virtio.c       | 19 +++++++++++++++++++
>  include/linux/virtio_config.h |  1 +
>  3 files changed, 48 insertions(+)
> 
LGTM.

I assume that this will go either via the virtio tree or via the s390
arch tree, i.e. not through virtio-ccw, right?

On Wed, Jul 15, 2020 at 10:31:09AM +0200, Pierre Morel
wrote:
> If protected virtualization is active on s390, the virtio queues are
> not accessible to the host, unless VIRTIO_F_IOMMU_PLATFORM has been
> negotiated. Use the new arch_validate_virtio_features() interface to
> fail probe if that's not the case, preventing a host error on access
> attempt.
> 
> Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>
> Reviewed-by: Cornelia Huck <cohuck at redhat.com>
> Acked-by: Halil Pasic <pasic at linux.ibm.com>
> Acked-by: Christian Borntraeger <borntraeger at de.ibm.com>
> ---
>  arch/s390/mm/init.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 6dc7c3b60ef6..d39af6554d4f 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -45,6 +45,7 @@
>  #include <asm/kasan.h>
>  #include <asm/dma-mapping.h>
>  #include <asm/uv.h>
> +#include <linux/virtio_config.h>
>  
>  pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
>  
> @@ -161,6 +162,33 @@ bool force_dma_unencrypted(struct device *dev)
>  	return is_prot_virt_guest();
>  }
>  
> +/*
> + * arch_validate_virtio_features
> + * @dev: the VIRTIO device being added
> + *
> + * Return an error if required features are missing on a guest running
> + * with protected virtualization.
> + */
> +int arch_validate_virtio_features(struct virtio_device *dev)
> +{
> +	if (!is_prot_virt_guest())
> +		return 0;
> +
> +	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
> +		dev_warn(&dev->dev,
> +			 "legacy virtio not supported with protected
virtualization\n");
> +		return -ENODEV;
> +	}
> +
> +	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
> +		dev_warn(&dev->dev,
> +			 "support for limited memory access required for protected
virtualization\n");
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +
>  /* protected virtualization */
>  static void pv_init(void)
>  {
What bothers me here is that arch code depends on virtio now.
It works even with a modular virtio when functions are inline,
but it seems fragile: e.g. it breaks virtio as an out of tree module,
since layout of struct virtio_device can change.

I'm not sure what to do with this yet, will try to think about it
over the weekend. Thanks!

> -- 
> 2.25.1