[Test code] Apply bit masks to allow some wrapping

In these cases, values are intentionally truncated, either to split them
into multiple values or to ensure that user-supplied data does not cause
Firecracker to panic with a try_from/unwrap failure.

Clippy will allow us to use "as" when we use bit masks to limit the size
of an explicitly-sized value (u16, u32, u64). It doesn't work on usize
values or on some more complicated expressions.

Signed-off-by: Jonathan Browne <[email protected]>

Author: JBYoshi

src/vmm/src/devices/bus.rs

@@ -90,13 +90,13 @@ pub struct ConstantDevice;
 impl ConstantDevice {
     pub fn bus_read(&mut self, offset: u64, data: &mut [u8]) {
         for (i, v) in data.iter_mut().enumerate() {
-            *v = (offset as u8) + (i as u8);
+            *v = ((offset + i as u64) & 0xff) as u8;
         }
     }
 
     fn bus_write(&mut self, offset: u64, data: &[u8]) {
         for (i, v) in data.iter().enumerate() {
-            assert_eq!(*v, (offset as u8) + (i as u8))
+            assert_eq!(*v, ((offset + i as u64) & 0xff) as u8)
         }
     }
 }

src/vmm/src/devices/virtio/balloon/device.rs

@@ -750,7 +750,10 @@ pub(crate) mod tests {
                     | (u64::from(*deflate_on_oom) << VIRTIO_BALLOON_F_DEFLATE_ON_OOM)
                     | ((u64::from(*stats_interval)) << VIRTIO_BALLOON_F_STATS_VQ);
 
-                assert_eq!(balloon.avail_features_by_page(0), features as u32);
+                assert_eq!(
+                    balloon.avail_features_by_page(0),
+                    (features & 0xFFFFFFFF) as u32
+                );
                 assert_eq!(balloon.avail_features_by_page(1), (features >> 32) as u32);
                 for i in 2..10 {
                     assert_eq!(balloon.avail_features_by_page(i), 0u32);

src/vmm/src/devices/virtio/block/device.rs

@@ -685,7 +685,7 @@ mod tests {
         let cfg = disk_properties.virtio_block_config_space();
         assert_eq!(cfg.len(), BLOCK_CONFIG_SPACE_SIZE);
         for (i, byte) in cfg.iter().enumerate() {
-            assert_eq!(*byte, (num_sectors >> (8 * i)) as u8);
+            assert_eq!(*byte, ((num_sectors >> (8 * i)) & 0xff) as u8);
         }
         // Testing `backing_file.virtio_block_disk_image_id()` implies
         // duplicating that logic in tests, so skipping it.
@@ -707,7 +707,10 @@ mod tests {
 
         let features: u64 = (1u64 << VIRTIO_F_VERSION_1) | (1u64 << VIRTIO_RING_F_EVENT_IDX);
 
-        assert_eq!(block.avail_features_by_page(0), features as u32);
+        assert_eq!(
+            block.avail_features_by_page(0),
+            (features & 0xffffffff) as u32,
+        );
         assert_eq!(block.avail_features_by_page(1), (features >> 32) as u32);
 
         for i in 2..10 {

src/vmm/src/devices/virtio/net/device.rs

@@ -959,7 +959,10 @@ pub mod tests {
             | 1 << VIRTIO_F_VERSION_1
             | 1 << VIRTIO_RING_F_EVENT_IDX;
 
-        assert_eq!(net.avail_features_by_page(0), features as u32);
+        assert_eq!(
+            net.avail_features_by_page(0),
+            (features & 0xFFFFFFFF) as u32,
+        );
         assert_eq!(net.avail_features_by_page(1), (features >> 32) as u32);
         for i in 2..10 {
             assert_eq!(net.avail_features_by_page(i), 0u32);

src/vmm/src/devices/virtio/rng/device.rs

@@ -391,7 +391,10 @@ mod tests {
 
         let features = 1 << VIRTIO_F_VERSION_1;
 
-        assert_eq!(entropy_dev.avail_features_by_page(0), features as u32);
+        assert_eq!(
+            entropy_dev.avail_features_by_page(0),
+            (features & 0xFFFFFFFF) as u32,
+        );
         assert_eq!(
             entropy_dev.avail_features_by_page(1),
             (features >> 32) as u32

src/vmm/src/devices/virtio/vsock/packet.rs

@@ -707,7 +707,9 @@ mod tests {
         assert_eq!(pkt.buf_addr.unwrap().raw_value(), buf_desc.addr.get());
 
         let zeros = vec![0_u8; pkt.buf_size()];
-        let data: Vec<u8> = (0..pkt.buf_size()).map(|i| (i % 0x100) as u8).collect();
+        let data: Vec<u8> = (0..pkt.buf_size())
+            .map(|i| ((i as u64) & 0xff) as u8)
+            .collect();
         for offset in 0..pkt.buf_size() {
             buf_desc.set_data(&zeros);