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

Cornelia Huck
2020-07-07T09:46:49Z

On Tue, 7 Jul 2020 10:44:37 +0200
Pierre Morel <pmorel@linux.ibm.com> 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@linux.ibm.com>
> ---
> 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;
> +}