Prevent foreign Rust exceptions from being caught

library/panic_unwind/src/emcc.rs

@@ -47,7 +47,12 @@ static EXCEPTION_TYPE_INFO: TypeInfo = TypeInfo {
     name: b"rust_panic\0".as_ptr(),
 };
 
+// NOTE(nbdd0121): The `canary` field will be part of stable ABI after `c_unwind` stabilization.
+#[repr(C)]
 struct Exception {
+    // See `gcc.rs` on why this is present. We already have a static here so just use it.
+    canary: *const TypeInfo,
+
     // This is necessary because C++ code can capture our exception with
     // std::exception_ptr and rethrow it multiple times, possibly even in
     // another thread.
@@ -70,27 +75,38 @@ pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
     let catch_data = &*(ptr as *mut CatchData);
 
     let adjusted_ptr = __cxa_begin_catch(catch_data.ptr as *mut libc::c_void) as *mut Exception;
-    let out = if catch_data.is_rust_panic {
-        let was_caught = (*adjusted_ptr).caught.swap(true, Ordering::SeqCst);
-        if was_caught {
-            // Since cleanup() isn't allowed to panic, we just abort instead.
-            intrinsics::abort();
-        }
-        (*adjusted_ptr).data.take().unwrap()
-    } else {
+    if !catch_data.is_rust_panic {
         super::__rust_foreign_exception();
-    };
+    }
+
+    let canary = ptr::addr_of!((*adjusted_ptr).canary).read();
+    if !ptr::eq(canary, &EXCEPTION_TYPE_INFO) {
+        super::__rust_foreign_exception();
+    }
+
+    let was_caught = (*adjusted_ptr).caught.swap(true, Ordering::SeqCst);
+    if was_caught {
+        // Since cleanup() isn't allowed to panic, we just abort instead.
+        intrinsics::abort();
+    }
+    let out = (*adjusted_ptr).data.take().unwrap();
     __cxa_end_catch();
     out
 }
 
 pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
-    let sz = mem::size_of_val(&data);
-    let exception = __cxa_allocate_exception(sz) as *mut Exception;
+    let exception = __cxa_allocate_exception(mem::size_of::<Exception>()) as *mut Exception;
     if exception.is_null() {
         return uw::_URC_FATAL_PHASE1_ERROR as u32;
     }
-    ptr::write(exception, Exception { caught: AtomicBool::new(false), data: Some(data) });
+    ptr::write(
+        exception,
+        Exception {
+            canary: &EXCEPTION_TYPE_INFO,
+            caught: AtomicBool::new(false),
+            data: Some(data),
+        },
+    );
     __cxa_throw(exception as *mut _, &EXCEPTION_TYPE_INFO, exception_cleanup);
 }
 

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 exist in a single process,
+// 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

library/panic_unwind/src/seh.rs

@@ -49,9 +49,15 @@
 use alloc::boxed::Box;
 use core::any::Any;
 use core::mem::{self, ManuallyDrop};
+use core::ptr;
 use libc::{c_int, c_uint, c_void};
 
+// NOTE(nbdd0121): The `canary` field will be part of stable ABI after `c_unwind` stabilization.
+#[repr(C)]
 struct Exception {
+    // See `gcc.rs` on why this is present. We already have a static here so just use it.
+    canary: *const _TypeDescriptor,
+
     // This needs to be an Option because we catch the exception by reference
     // and its destructor is executed by the C++ runtime. When we take the Box
     // out of the exception, we need to leave the exception in a valid state
@@ -235,7 +241,7 @@ static mut TYPE_DESCRIPTOR: _TypeDescriptor = _TypeDescriptor {
 macro_rules! define_cleanup {
     ($abi:tt $abi2:tt) => {
         unsafe extern $abi fn exception_cleanup(e: *mut Exception) {
-            if let Exception { data: Some(b) } = e.read() {
+            if let Exception { data: Some(b), .. } = e.read() {
                 drop(b);
                 super::__rust_drop_panic();
             }
@@ -265,7 +271,7 @@ pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
     // The ManuallyDrop is needed here since we don't want Exception to be
     // dropped when unwinding. Instead it will be dropped by exception_cleanup
     // which is invoked by the C++ runtime.
-    let mut exception = ManuallyDrop::new(Exception { data: Some(data) });
+    let mut exception = ManuallyDrop::new(Exception { canary: &TYPE_DESCRIPTOR, data: Some(data) });
     let throw_ptr = &mut exception as *mut _ as *mut _;
 
     // This... may seems surprising, and justifiably so. On 32-bit MSVC the
@@ -321,8 +327,12 @@ pub unsafe fn cleanup(payload: *mut u8) -> Box<dyn Any + Send> {
     // __rust_try. This happens when a non-Rust foreign exception is caught.
     if payload.is_null() {
         super::__rust_foreign_exception();
-    } else {
-        let exception = &mut *(payload as *mut Exception);
-        exception.data.take().unwrap()
     }
+    let exception = payload as *mut Exception;
+    let canary = ptr::addr_of!((*exception).canary).read();
+    if !ptr::eq(canary, &TYPE_DESCRIPTOR) {
+        // A foreign Rust exception.
+        super::__rust_foreign_exception();
+    }
+    (*exception).data.take().unwrap()
 }

src/test/run-make-fulldeps/foreign-rust-exceptions/Makefile

@@ -0,0 +1,11 @@
+# ignore-i686-pc-windows-gnu
+
+# This test doesn't work on 32-bit MinGW as cdylib has its own copy of unwinder
+# so cross-DLL unwinding does not work.
+
+include ../tools.mk
+
+all:
+	$(RUSTC) bar.rs --crate-type=cdylib
+	$(RUSTC) foo.rs
+	$(call RUN,foo) 2>&1 | $(CGREP) "Rust cannot catch foreign exceptions"

src/test/run-make-fulldeps/foreign-rust-exceptions/bar.rs

@@ -0,0 +1,7 @@
+#![crate_type = "cdylib"]
+#![feature(c_unwind)]
+
+#[no_mangle]
+extern "C-unwind" fn panic() {
+    panic!();
+}

src/test/run-make-fulldeps/foreign-rust-exceptions/foo.rs

@@ -0,0 +1,13 @@
+#![feature(c_unwind)]
+
+#[cfg_attr(not(windows), link(name = "bar"))]
+#[cfg_attr(windows, link(name = "bar.dll"))]
+extern "C-unwind" {
+    fn panic();
+}
+
+fn main() {
+    let _ = std::panic::catch_unwind(|| {
+        unsafe { panic() };
+    });
+}