Prevent foreign Rust exceptions from being caught

Author: nbdd0121

library/panic_unwind/src/gcc.rs

@@ -38,12 +38,23 @@
 
 use alloc::boxed::Box;
 use core::any::Any;
+use core::ptr;
 
 use unwind as uw;
 
+// In case where multiple copies of std is compiled into a single binary,
+// we use address of this static variable to distinguish an exception raised by
+// this copy and some other copy (which needs to be treated as foreign exception).
+static CANARY: u8 = 0;
+
+// NOTE(nbdd0121)
+// Once `c_unwind` feature is stabilized, there will be ABI stability requirement
+// on this struct. The first two field must be `_Unwind_Exception` and `canary`,
+// as it may be accessed by a different version of the std with a different compiler.
 #[repr(C)]
 struct Exception {
     _uwe: uw::_Unwind_Exception,
+    canary: *const u8,
     cause: Box<dyn Any + Send>,
 }
 
@@ -54,6 +65,7 @@ pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
             exception_cleanup,
             private: [0; uw::unwinder_private_data_size],
         },
+        canary: &CANARY,
         cause: data,
     });
     let exception_param = Box::into_raw(exception) as *mut uw::_Unwind_Exception;
@@ -75,10 +87,22 @@ pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
     if (*exception).exception_class != rust_exception_class() {
         uw::_Unwind_DeleteException(exception);
         super::__rust_foreign_exception();
-    } else {
-        let exception = Box::from_raw(exception as *mut Exception);
-        exception.cause
     }
+
+    let exception = exception.cast::<Exception>();
+    // Just access the canary field, avoid accessing the entire `Exception` as
+    // it can be a foreign Rust exception.
+    let canary = ptr::addr_of!((*exception).canary).read();
+    if !ptr::eq(canary, &CANARY) {
+        // A foreign Rust exception, treat it slightly differently from other
+        // foreign exceptions, because call into `_Unwind_DeleteException` will
+        // call into `__rust_drop_panic` which produces a confusing
+        // "Rust panic must be rethrown" message.
+        super::__rust_foreign_exception();
+    }
+
+    let exception = Box::from_raw(exception as *mut Exception);
+    exception.cause
 }
 
 // Rust's exception class identifier.  This is used by personality routines to