Re: [PATCH v4 2/2] s390: virtio: PV needs VIRTIO I/O device protection

[Cornelia Huck]

On Tue,  7 Jul 2020 10:44:37 +0200
Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:

> S390, protecting the guest memory against unauthorized host access
> needs to enforce VIRTIO I/O device protection through the use of
> VIRTIO_F_VERSION_1 and VIRTIO_F_IOMMU_PLATFORM.

Hm... what about:

"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
enforce this."

> 
> Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> ---
>  arch/s390/kernel/uv.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index c296e5c8dbf9..106330f6eda1 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -14,6 +14,7 @@
>  #include <linux/memblock.h>
>  #include <linux/pagemap.h>
>  #include <linux/swap.h>
> +#include <linux/virtio_config.h>
>  #include <asm/facility.h>
>  #include <asm/sections.h>
>  #include <asm/uv.h>
> @@ -413,3 +414,27 @@ static int __init uv_info_init(void)
>  }
>  device_initcall(uv_info_init);
>  #endif
> +
> +/*
> + * arch_validate_virtio_iommu_platform

s/arch_validate_virtio_iommu_platform/arch_validate_virtio_features/

> + * @dev: the VIRTIO device being added
> + *
> + * Return value: returns -ENODEV if any features of the
> + *               device breaks the protected virtualization
> + *               0 otherwise.

I don't think you need to specify the contract here: that belongs to
the definition in the virtio core. What about simply adding a sentence
"Return an error if required features are missing on a guest running
with protected virtualization." ?

> + */
> +int arch_validate_virtio_features(struct virtio_device *dev)
> +{

Maybe jump out immediately if the guest is not protected?

> +	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
> +		dev_warn(&dev->dev, "device must provide VIRTIO_F_VERSION_1\n");
> +		return is_prot_virt_guest() ? -ENODEV : 0;
> +	}
> +
> +	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
> +		dev_warn(&dev->dev,
> +			 "device must provide VIRTIO_F_IOMMU_PLATFORM\n");
> +		return is_prot_virt_guest() ? -ENODEV : 0;
> +	}

if (!is_prot_virt_guest())
	return 0;

if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
	dev_warn(&dev->dev,
                 "legacy virtio is incompatible with protected guests");
	return -ENODEV;
}

if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
	dev_warn(&dev->dev,
		 "device does not work with limited memory access in protected guests");
	return -ENODEV;
}

> +
> +	return 0;
> +}