Linux Virtualization - Jun 2020 - [PATCH v2 0/1] s390: virtio: let's arch choose to accept devices without IOMMU feature

An architecture protecting the guest memory against unauthorized host
access may want to enforce VIRTIO I/O device protection through the
use of VIRTIO_F_IOMMU_PLATFORM.

Let's give a chance to the architecture to accept or not devices
without VIRTIO_F_IOMMU_PLATFORM.

Pierre Morel (1):
  s390: virtio: let arch accept devices without IOMMU feature

 arch/s390/mm/init.c     | 6 ++++++
 drivers/virtio/virtio.c | 9 +++++++++
 include/linux/virtio.h  | 2 ++
 3 files changed, 17 insertions(+)

-- 
2.25.1

Changelog 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 protecting the guest memory against unauthorized host
access may want to enforce VIRTIO I/O device protection through the
use of VIRTIO_F_IOMMU_PLATFORM.

Let's give a chance to the architecture to accept or not devices
without VIRTIO_F_IOMMU_PLATFORM.

Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>
---
 arch/s390/mm/init.c     | 6 ++++++
 drivers/virtio/virtio.c | 9 +++++++++
 include/linux/virtio.h  | 2 ++
 3 files changed, 17 insertions(+)

diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 87b2d024e75a..3f04ad09650f 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -46,6 +46,7 @@
 #include <asm/kasan.h>
 #include <asm/dma-mapping.h>
 #include <asm/uv.h>
+#include <linux/virtio.h>
 
 pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
 
@@ -162,6 +163,11 @@ bool force_dma_unencrypted(struct device *dev)
 	return is_prot_virt_guest();
 }
 
+int arch_needs_iommu_platform(struct virtio_device *dev) 
+{
+	return is_prot_virt_guest();
+}
+
 /* protected virtualization */
 static void pv_init(void)
 {
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index a977e32a88f2..30091089bee8 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -167,6 +167,11 @@ void virtio_add_status(struct virtio_device *dev, unsigned
int status)
 }
 EXPORT_SYMBOL_GPL(virtio_add_status);
 
+int __weak arch_needs_iommu_platform(struct virtio_device *dev)
+{
+	return 0;
+}
+
 int virtio_finalize_features(struct virtio_device *dev)
 {
 	int ret = dev->config->finalize_features(dev);
@@ -179,6 +184,10 @@ int virtio_finalize_features(struct virtio_device *dev)
 	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
 		return 0;
 
+	if (arch_needs_iommu_platform(dev) &&
+		!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM))
+		return -EIO;
+
 	virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
 	status = dev->config->get_status(dev);
 	if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index a493eac08393..2c46b310c38c 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -195,4 +195,6 @@ void unregister_virtio_driver(struct virtio_driver *drv);
 #define module_virtio_driver(__virtio_driver) \
 	module_driver(__virtio_driver, register_virtio_driver, \
 			unregister_virtio_driver)
+
+int arch_needs_iommu_platform(struct virtio_device *dev);
 #endif /* _LINUX_VIRTIO_H */
-- 
2.25.1

On 2020/6/15 ??8:39, Pierre Morel wrote:
> An architecture protecting the guest memory against unauthorized host
> access may want to enforce VIRTIO I/O device protection through the
> use of VIRTIO_F_IOMMU_PLATFORM.
>
> Let's give a chance to the architecture to accept or not devices
> without VIRTIO_F_IOMMU_PLATFORM.
>
> Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>

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

> ---
>   arch/s390/mm/init.c     | 6 ++++++
>   drivers/virtio/virtio.c | 9 +++++++++
>   include/linux/virtio.h  | 2 ++
>   3 files changed, 17 insertions(+)
>
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 87b2d024e75a..3f04ad09650f 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -46,6 +46,7 @@
>   #include <asm/kasan.h>
>   #include <asm/dma-mapping.h>
>   #include <asm/uv.h>
> +#include <linux/virtio.h>
>   
>   pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
>   
> @@ -162,6 +163,11 @@ bool force_dma_unencrypted(struct device *dev)
>   	return is_prot_virt_guest();
>   }
>   
> +int arch_needs_iommu_platform(struct virtio_device *dev)
> +{
> +	return is_prot_virt_guest();
> +}
> +
>   /* protected virtualization */
>   static void pv_init(void)
>   {
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index a977e32a88f2..30091089bee8 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -167,6 +167,11 @@ void virtio_add_status(struct virtio_device *dev,
unsigned int status)
>   }
>   EXPORT_SYMBOL_GPL(virtio_add_status);
>   
> +int __weak arch_needs_iommu_platform(struct virtio_device *dev)
> +{
> +	return 0;
> +}
> +
>   int virtio_finalize_features(struct virtio_device *dev)
>   {
>   	int ret = dev->config->finalize_features(dev);
> @@ -179,6 +184,10 @@ int virtio_finalize_features(struct virtio_device
*dev)
>   	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
>   		return 0;
>   
> +	if (arch_needs_iommu_platform(dev) &&
> +		!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM))
> +		return -EIO;
> +
>   	virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
>   	status = dev->config->get_status(dev);
>   	if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index a493eac08393..2c46b310c38c 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -195,4 +195,6 @@ void unregister_virtio_driver(struct virtio_driver
*drv);
>   #define module_virtio_driver(__virtio_driver) \
>   	module_driver(__virtio_driver, register_virtio_driver, \
>   			unregister_virtio_driver)
> +
> +int arch_needs_iommu_platform(struct virtio_device *dev);
>   #endif /* _LINUX_VIRTIO_H */

On 15.06.20 14:39, Pierre Morel wrote:
> An architecture protecting the guest memory against unauthorized host
> access may want to enforce VIRTIO I/O device protection through the
> use of VIRTIO_F_IOMMU_PLATFORM.
> 
> Let's give a chance to the architecture to accept or not devices
> without VIRTIO_F_IOMMU_PLATFORM.
> 
> Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>

Acked-by: Christian Borntraeger <borntraeger at de.ibm.com>

Shouldnt we maybe add a pr_warn if that happens to help the admins to understand
what is going on?

> ---
>  arch/s390/mm/init.c     | 6 ++++++
>  drivers/virtio/virtio.c | 9 +++++++++
>  include/linux/virtio.h  | 2 ++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 87b2d024e75a..3f04ad09650f 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -46,6 +46,7 @@
>  #include <asm/kasan.h>
>  #include <asm/dma-mapping.h>
>  #include <asm/uv.h>
> +#include <linux/virtio.h>
>  
>  pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
>  
> @@ -162,6 +163,11 @@ bool force_dma_unencrypted(struct device *dev)
>  	return is_prot_virt_guest();
>  }
>  
> +int arch_needs_iommu_platform(struct virtio_device *dev) 
> +{
> +	return is_prot_virt_guest();
> +}
> +
>  /* protected virtualization */
>  static void pv_init(void)
>  {
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index a977e32a88f2..30091089bee8 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -167,6 +167,11 @@ void virtio_add_status(struct virtio_device *dev,
unsigned int status)
>  }
>  EXPORT_SYMBOL_GPL(virtio_add_status);
>  
> +int __weak arch_needs_iommu_platform(struct virtio_device *dev)
> +{
> +	return 0;
> +}
> +
>  int virtio_finalize_features(struct virtio_device *dev)
>  {
>  	int ret = dev->config->finalize_features(dev);
> @@ -179,6 +184,10 @@ int virtio_finalize_features(struct virtio_device
*dev)
>  	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
>  		return 0;
>  
> +	if (arch_needs_iommu_platform(dev) &&
> +		!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM))
> +		return -EIO;
> +
>  	virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
>  	status = dev->config->get_status(dev);
>  	if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index a493eac08393..2c46b310c38c 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -195,4 +195,6 @@ void unregister_virtio_driver(struct virtio_driver
*drv);
>  #define module_virtio_driver(__virtio_driver) \
>  	module_driver(__virtio_driver, register_virtio_driver, \
>  			unregister_virtio_driver)
> +
> +int arch_needs_iommu_platform(struct virtio_device *dev);
>  #endif /* _LINUX_VIRTIO_H */
>

On Mon, 15 Jun 2020 14:39:24 +0200
Pierre Morel <pmorel at linux.ibm.com> wrote:

I find the subject (commit short) sub optimal. The 'arch' is already
accepting devices 'without IOMMU feature'. What you are introducing is
the ability to reject.
> An architecture protecting the guest memory against unauthorized host
> access may want to enforce VIRTIO I/O device protection through the
> use of VIRTIO_F_IOMMU_PLATFORM.
> 
> Let's give a chance to the architecture to accept or not devices
> without VIRTIO_F_IOMMU_PLATFORM.
> 
I don't particularly like the commit message. In general, I believe
using access_platform instead of iommu_platform would really benefit us.
> Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>
> ---
>  arch/s390/mm/init.c     | 6 ++++++
>  drivers/virtio/virtio.c | 9 +++++++++
>  include/linux/virtio.h  | 2 ++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 87b2d024e75a..3f04ad09650f 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -46,6 +46,7 @@
>  #include <asm/kasan.h>
>  #include <asm/dma-mapping.h>
>  #include <asm/uv.h>
> +#include <linux/virtio.h>
arch/s390/mm/init.c including virtio.h looks a bit strange to me, but
if Heiko and Vasily don't mind, neither do I.
>  
>  pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
>  
> @@ -162,6 +163,11 @@ bool force_dma_unencrypted(struct device *dev)
>  	return is_prot_virt_guest();
>  }
>  
> +int arch_needs_iommu_platform(struct virtio_device *dev) 
Maybe prefixing the name with virtio_ would help provide the
proper context.
> +{
> +	return is_prot_virt_guest();
> +}
> +
>  /* protected virtualization */
>  static void pv_init(void)
>  {
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index a977e32a88f2..30091089bee8 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -167,6 +167,11 @@ void virtio_add_status(struct virtio_device *dev,
unsigned int status)
>  }
>  EXPORT_SYMBOL_GPL(virtio_add_status);
>  
> +int __weak arch_needs_iommu_platform(struct virtio_device *dev)
> +{
> +	return 0;
> +}
> +
Adding some people that could be interested in overriding this as well
to the cc list.
>  int virtio_finalize_features(struct virtio_device *dev)
>  {
>  	int ret = dev->config->finalize_features(dev);
> @@ -179,6 +184,10 @@ int virtio_finalize_features(struct virtio_device
*dev)
>  	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
>  		return 0;
>  
> +	if (arch_needs_iommu_platform(dev) &&
> +		!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM))
> +		return -EIO;
> +
Why EIO?

Overall, I think it is a good idea to have something that is going to
protect us from this scenario.

Regards,
Halil
>  	virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
>  	status = dev->config->get_status(dev);
>  	if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index a493eac08393..2c46b310c38c 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -195,4 +195,6 @@ void unregister_virtio_driver(struct virtio_driver
*drv);
>  #define module_virtio_driver(__virtio_driver) \
>  	module_driver(__virtio_driver, register_virtio_driver, \
>  			unregister_virtio_driver)
> +
> +int arch_needs_iommu_platform(struct virtio_device *dev);
>  #endif /* _LINUX_VIRTIO_H */