Fix panic hook leaking after each new sandbox (#827)

Signed-off-by: Ludvig Liljenberg <4257730+ludfjig@users.noreply.github.com>

Author: ludfjig

src/hyperlight_host/src/signal_handlers/mod.rs

@@ -29,26 +29,31 @@ pub(crate) fn setup_signal_handlers(config: &SandboxConfiguration) -> crate::Res
     // should be safe to call.
     #[cfg(feature = "seccomp")]
     {
+        use std::sync::Once;
+
         vmm_sys_util::signal::register_signal_handler(
             libc::SIGSYS,
             sigsys_signal_handler::handle_sigsys,
         )
         .map_err(crate::HyperlightError::VmmSysError)?;
 
-        let original_hook = std::panic::take_hook();
-        // Set a custom panic hook that checks for "DisallowedSyscall"
-        std::panic::set_hook(Box::new(move |panic_info| {
-            // Check if the panic payload matches "DisallowedSyscall"
-            if let Some(crate::HyperlightError::DisallowedSyscall) = panic_info
-                .payload()
-                .downcast_ref::<crate::HyperlightError>(
-            ) {
-                // Do nothing to avoid superfluous syscalls
-                return;
-            }
-            // If not "DisallowedSyscall", use the original hook
-            original_hook(panic_info);
-        }));
+        static PANIC_HOOK_INIT: Once = Once::new();
+        PANIC_HOOK_INIT.call_once(|| {
+            let original_hook = std::panic::take_hook();
+            // Set a custom panic hook that checks for "DisallowedSyscall"
+            std::panic::set_hook(Box::new(move |panic_info| {
+                // Check if the panic payload matches "DisallowedSyscall"
+                if let Some(crate::HyperlightError::DisallowedSyscall) = panic_info
+                    .payload()
+                    .downcast_ref::<crate::HyperlightError>(
+                ) {
+                    // Do nothing to avoid superfluous syscalls
+                    return;
+                }
+                // If not "DisallowedSyscall", use the original hook
+                original_hook(panic_info);
+            }));
+        });
     }
     vmm_sys_util::signal::register_signal_handler(
         libc::SIGRTMIN() + config.get_interrupt_vcpu_sigrtmin_offset() as c_int,