Linux Virtualization - Aug 2020 - [PATCH v8 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:

I use the original idea from Connie for an optional
arch_has_restricted_memory_access.

I renamed the callback accordingly, added the definition of
ARCH_HAS_RESTRICTED_MEMORY_ACCESS inside the VIRTIO Kconfig
and the selection in the PROTECTED_VIRTUALIZATION_GUEST
config entry.


Regards,
Pierre

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

 arch/s390/Kconfig             |  1 +
 arch/s390/mm/init.c           | 30 ++++++++++++++++++++++++++++++
 drivers/virtio/Kconfig        |  6 ++++++
 drivers/virtio/virtio.c       |  4 ++++
 include/linux/virtio_config.h |  9 +++++++++
 5 files changed, 50 insertions(+)

-- 
2.25.1

Changelog

to v8:

- refactoring by using an optional callback
  (Connie)

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.

Provide a new Kconfig entry, CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS,
the architecture can select when it provides a callback named
arch_has_restricted_memory_access to validate the virtio device
features.

Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>
---
 drivers/virtio/Kconfig        | 6 ++++++
 drivers/virtio/virtio.c       | 4 ++++
 include/linux/virtio_config.h | 9 +++++++++
 3 files changed, 19 insertions(+)

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 5809e5f5b157..eef09e3c92f9 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -6,6 +6,12 @@ config VIRTIO
 	  bus, such as CONFIG_VIRTIO_PCI, CONFIG_VIRTIO_MMIO, CONFIG_RPMSG
 	  or CONFIG_S390_GUEST.
 
+config ARCH_HAS_RESTRICTED_MEMORY_ACCESS
+	bool
+	help
+	  This option is selected by any architecture enforcing
+	  VIRTIO_F_IOMMU_PLATFORM
+
 menuconfig VIRTIO_MENU
 	bool "Virtio drivers"
 	default y
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index a977e32a88f2..1471db7d6510 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -176,6 +176,10 @@ int virtio_finalize_features(struct virtio_device *dev)
 	if (ret)
 		return ret;
 
+	ret = arch_has_restricted_memory_access(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..f6b82541c497 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -459,4 +459,13 @@ static inline void virtio_cwrite64(struct virtio_device
*vdev,
 		_r;							\
 	})
 
+#ifdef CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS
+int arch_has_restricted_memory_access(struct virtio_device *dev);
+#else
+static inline int arch_has_restricted_memory_access(struct virtio_device *dev)
+{
+	return 0;
+}
+#endif /* CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS */
+
 #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.
Define CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS and export
arch_has_restricted_memory_access 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>
---
 arch/s390/Kconfig   |  1 +
 arch/s390/mm/init.c | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 9cfd8de907cb..d4a3ef4fa27b 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -820,6 +820,7 @@ menu "Virtualization"
 config PROTECTED_VIRTUALIZATION_GUEST
 	def_bool n
 	prompt "Protected virtualization guest support"
+	select ARCH_HAS_RESTRICTED_MEMORY_ACCESS
 	help
 	  Select this option, if you want to be able to run this
 	  kernel as a protected virtualization KVM guest.
diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 6dc7c3b60ef6..aec04d7dd089 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 +162,35 @@ bool force_dma_unencrypted(struct device *dev)
 	return is_prot_virt_guest();
 }
 
+#ifdef CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS
+/*
+ * arch_has_restricted_memory_access
+ * @dev: the VIRTIO device being added
+ *
+ * Return an error if required features are missing on a guest running
+ * with protected virtualization.
+ */
+int arch_has_restricted_memory_access(struct virtio_device *dev)
+{
+	if (!is_prot_virt_guest())
+		return 0;
+
+	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
+		dev_warn(&dev->dev, "device must provide
VIRTIO_F_VERSION_1\n");
+		return -ENODEV;
+	}
+
+	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
+		dev_warn(&dev->dev,
+			 "device must provide VIRTIO_F_IOMMU_PLATFORM\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(arch_has_restricted_memory_access);
+#endif
+
 /* protected virtualization */
 static void pv_init(void)
 {
-- 
2.25.1

On Tue, 18 Aug 2020 16:58:30 +0200
Pierre Morel <pmorel at linux.ibm.com> wrote:
> An architecture may need to validate the VIRTIO devices features
> based on architecture specifics.
> 
> Provide a new Kconfig entry, CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS,
> the architecture can select when it provides a callback named
> arch_has_restricted_memory_access to validate the virtio device
> features.
> 
> Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>
> ---
>  drivers/virtio/Kconfig        | 6 ++++++
>  drivers/virtio/virtio.c       | 4 ++++
>  include/linux/virtio_config.h | 9 +++++++++
>  3 files changed, 19 insertions(+)
> 
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 5809e5f5b157..eef09e3c92f9 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -6,6 +6,12 @@ config VIRTIO
>  	  bus, such as CONFIG_VIRTIO_PCI, CONFIG_VIRTIO_MMIO, CONFIG_RPMSG
>  	  or CONFIG_S390_GUEST.
>  
> +config ARCH_HAS_RESTRICTED_MEMORY_ACCESS
> +	bool
> +	help
> +	  This option is selected by any architecture enforcing
> +	  VIRTIO_F_IOMMU_PLATFORM
This option is only for a very specific case of "restricted memory
access", namely the kind that requires IOMMU_PLATFORM for virtio
devices. ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS? Or is this intended
to cover cases outside of virtio as well?
> +
>  menuconfig VIRTIO_MENU
>  	bool "Virtio drivers"
>  	default y
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index a977e32a88f2..1471db7d6510 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -176,6 +176,10 @@ int virtio_finalize_features(struct virtio_device
*dev)
>  	if (ret)
>  		return ret;
>  
> +	ret = arch_has_restricted_memory_access(dev);
> +	if (ret)
> +		return ret;
Hm, I'd rather have expected something like

if (arch_has_restricted_memory_access(dev)) {
	// enforce VERSION_1 and IOMMU_PLATFORM
}

Otherwise, you're duplicating the checks in the individual architecture
callbacks again.

[Not sure whether the device argument would be needed here; are there
architectures where we'd only require IOMMU_PLATFORM for a subset of
virtio devices?]
> +
>  	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..f6b82541c497 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -459,4 +459,13 @@ static inline void virtio_cwrite64(struct
virtio_device *vdev,
>  		_r;							\
>  	})
>  
> +#ifdef CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS
> +int arch_has_restricted_memory_access(struct virtio_device *dev);
> +#else
> +static inline int arch_has_restricted_memory_access(struct virtio_device
*dev)
> +{
> +	return 0;
> +}
> +#endif /* CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS */
> +
>  #endif /* _LINUX_VIRTIO_CONFIG_H */

On Tue, 18 Aug 2020 16:58:31 +0200
Pierre Morel <pmorel at linux.ibm.com> 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.
> Define CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS and export
> arch_has_restricted_memory_access 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>
> ---
>  arch/s390/Kconfig   |  1 +
>  arch/s390/mm/init.c | 30 ++++++++++++++++++++++++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index 9cfd8de907cb..d4a3ef4fa27b 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -820,6 +820,7 @@ menu "Virtualization"
>  config PROTECTED_VIRTUALIZATION_GUEST
>  	def_bool n
>  	prompt "Protected virtualization guest support"
> +	select ARCH_HAS_RESTRICTED_MEMORY_ACCESS
>  	help
>  	  Select this option, if you want to be able to run this
>  	  kernel as a protected virtualization KVM guest.
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 6dc7c3b60ef6..aec04d7dd089 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 +162,35 @@ bool force_dma_unencrypted(struct device *dev)
>  	return is_prot_virt_guest();
>  }
>  
> +#ifdef CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS
> +/*
> + * arch_has_restricted_memory_access
> + * @dev: the VIRTIO device being added
> + *
> + * Return an error if required features are missing on a guest running
> + * with protected virtualization.
> + */
> +int arch_has_restricted_memory_access(struct virtio_device *dev)
> +{
> +	if (!is_prot_virt_guest())
> +		return 0;
If you just did a

return is_prot_virt_guest();

and did the virtio feature stuff in the virtio core, this function
would be short and sweet :)
> +
> +	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
> +		dev_warn(&dev->dev, "device must provide
VIRTIO_F_VERSION_1\n");
> +		return -ENODEV;
> +	}
> +
> +	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
> +		dev_warn(&dev->dev,
> +			 "device must provide VIRTIO_F_IOMMU_PLATFORM\n");
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(arch_has_restricted_memory_access);
> +#endif
> +
>  /* protected virtualization */
>  static void pv_init(void)
>  {