runtime-rs: Enables block device and disable virtio-fs via capabilities

Kata runtime employs a CapabilityBits mechanism for VMM capability
governance. Fundamentally, this mechanism utilizes predefined feature
flags to manage the VMM's operational boundaries.

To meet demands for storage performance and security, it's necessary
to explicitly enable capability flags such as `BlockDeviceSupport`
(basic block device support) and `BlockDeviceHotplugSupport` (block
device hotplug) which ensures the VMM provides the expected caps.

In CoCo scenarios, due to the potential risks of sensitive data leaks
or side-channel attacks introduced by virtio-fs through shared file
systems, the `FsSharingSupport` flag must be forcibly disabled. This
disables the virtio-fs feature at the capability set level, blocking
insecure data channels.

Fixes #11341

Signed-off-by: alex.lyn <alex.lyn@antgroup.com>

src/runtime-rs/crates/hypervisor/src/qemu/inner.rs

@@ -379,7 +379,17 @@ impl QemuInner {
 
     pub(crate) async fn capabilities(&self) -> Result<Capabilities> {
         let mut caps = Capabilities::default();
-        caps.set(CapabilityBits::FsSharingSupport);
+
+        // Confidential Guest doesn't permit virtio-fs.
+        let flags = if self.hypervisor_config().security_info.confidential_guest {
+            CapabilityBits::BlockDeviceSupport | CapabilityBits::BlockDeviceHotplugSupport
+        } else {
+            CapabilityBits::BlockDeviceSupport
+                | CapabilityBits::BlockDeviceHotplugSupport
+                | CapabilityBits::FsSharingSupport
+        };
+        caps.set(flags);
+
         Ok(caps)
     }