On 2020-07-07 11:46, Cornelia Huck wrote:

On Tue,  7 Jul 2020 10:44:37 +0200
Pierre Morel [off-list ref] wrote:

quoted

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."

Yes, thanks.

quoted

Signed-off-by: Pierre Morel <redacted>
---
  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/

quoted

+ * @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." ?

OK, right.

quoted

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

Maybe jump out immediately if the guest is not protected?

quoted

+	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;
}

Yes, easier to read.

Thanks,
Pierre


-- 
Pierre Morel
IBM Lab Boeblingen