fix(virtq): truncate error message so it fits completion

Signed-off-by: Tomasz Andrzejak <andreiltd@gmail.com>

Author: andreiltd

src/hyperlight_host/src/sandbox/outb.rs

@@ -268,12 +268,23 @@ fn outb_virtq_call(
 
     let name = call.function_name.clone();
     let args: Vec<ParameterValue> = call.parameters.unwrap_or(vec![]);
-    let res = host_funcs
+
+    let registry = host_funcs
         .try_lock()
-        .map_err(|e| HandleOutbError::LockFailed(file!(), line!(), e.to_string()))?
+        .map_err(|e| HandleOutbError::LockFailed(file!(), line!(), e.to_string()))?;
+
+    let mut res = registry
         .call_host_function(&name, args)
         .map_err(|e| GuestError::new(ErrorCode::HostFunctionError, e.to_string()));
 
+    // Truncate oversized error messages so the serialized response
+    // fits in the completion buffer the guest pre-allocated.
+    if let Err(err) = &mut res
+        && err.message.len() > wc.capacity()
+    {
+        err.message.truncate(wc.capacity());
+    }
+
     // Serialize response: VirtqMsgHeader + FunctionCallResult
     let func_result = FunctionCallResult::new(res);
     let mut builder = flatbuffers::FlatBufferBuilder::new();

src/hyperlight_host/tests/integration_test.rs

@@ -536,7 +536,7 @@ fn guest_malloc_abort() {
     });
 
     // allocate a vector (on heap) that is bigger than the heap
-    let heap_size = 0x4000;
+    let heap_size = 0x8000;
     let size_to_allocate = 0x10000;
     assert!(
         size_to_allocate > heap_size,
@@ -585,7 +585,7 @@ fn guest_outb_with_invalid_port_poisons_sandbox() {
 
 #[test]
 fn guest_panic_no_alloc() {
-    let heap_size = 0x4000;
+    let heap_size = 0x8000;
 
     let mut cfg = SandboxConfiguration::default();
     cfg.set_heap_size(heap_size);