virtio: queue: Enforce DescriptorChain ordering

The virtio spec requires that all read-only descriptors appear in the
chain before any write-only descriptors.  Enforce this in the
`checked_new` function by adding a new `required_flags` parameter.  The
`next_descriptor` function will set this to `VIRTQ_DESC_F_WRITE` if the
current descriptor is write-only.  This ensures that once we see a
write-only descriptor, all following descriptors must be write-only.

BUG=b:136127316
TEST=none

Change-Id: Id8f942a4236a20f62f35439f3648dbec17e14c00
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/1757239
Auto-Submit: Chirantan Ekbote <chirantan@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Stephen Barber <smbarber@chromium.org>
Commit-Queue: Chirantan Ekbote <chirantan@chromium.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/devices/src/virtio/descriptor_utils.rs b/devices/src/virtio/descriptor_utils.rs
index 2233931..409134e 100644
--- a/devices/src/virtio/descriptor_utils.rs
+++ b/devices/src/virtio/descriptor_utils.rs
@@ -517,7 +517,8 @@ pub fn create_descriptor_chain(
         );
     }
 
-    DescriptorChain::checked_new(memory, descriptor_array_addr, 0x100, 0).ok_or(Error::InvalidChain)
+    DescriptorChain::checked_new(memory, descriptor_array_addr, 0x100, 0, 0)
+        .ok_or(Error::InvalidChain)
 }
 
 #[cfg(test)]