added regression test for underflow error

While loading an invalid bzimage the linux loader could crash because of
underflow. This tests is a regression test for the bug fix.

Signed-off-by: Andreea Florescu <[email protected]>

Author: andreeaflorescu

coverage_config_x86_64.json

@@ -1,5 +1,5 @@
 {
-  "coverage_score": 80.0,
+  "coverage_score": 81.0,
   "exclude_path": "",
   "crate_features": "bzimage,elf",
   "exclude_path": "benches/,loader_gen/"

src/loader/x86_64/bzimage/invalid_bzimage.bin

@@ -270,4 +270,32 @@ mod tests {
             .err()
         );
     }
+
+    #[test]
+    fn test_invalid_bzimage_underflow() {
+        use super::super::super::Error as LoaderError;
+
+        let path = concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/src/loader/x86_64/bzimage/invalid_bzimage.bin"
+        );
+
+        let gm = create_guest_mem();
+        let mut image = File::open(path).unwrap();
+        let kernel_offset = GuestAddress(0x200000);
+        let highmem_start_address = GuestAddress(0x0);
+
+        // load bzImage with good kernel_offset and himem_start setting
+        let loader_result = BzImage::load(
+            &gm,
+            Some(kernel_offset),
+            &mut image,
+            Some(highmem_start_address),
+        );
+
+        assert_eq!(
+            loader_result.unwrap_err(),
+            LoaderError::Bzimage(Error::Underflow)
+        );
+    }
 }