also consider boxes like unique references

src/stacked_borrows.rs

@@ -661,14 +661,14 @@ impl<'a, 'mir, 'tcx> EvalContextExt<'tcx> for MiriEvalContext<'a, 'mir, 'tcx> {
             // Primitives of reference type, that is the one thing we are interested in.
             fn visit_primitive(&mut self, place: MPlaceTy<'tcx, Borrow>) -> EvalResult<'tcx>
             {
-                match place.layout.ty.sty {
-                    ty::Ref(_, _, mutbl) => {
-                        let val = self.ecx.read_immediate(place.into())?;
-                        let val = self.ecx.retag_reference(val, mutbl)?;
-                        self.ecx.write_immediate(val, place.into())?;
-                    }
-                    _ => {}, // nothing to do
-                }
+                let mutbl = match place.layout.ty.sty {
+                    ty::Ref(_, _, mutbl) => mutbl,
+                    ty::Adt(..) if place.layout.ty.is_box() => MutMutable,
+                    _ => return Ok(()), // nothing to do
+                };
+                let val = self.ecx.read_immediate(place.into())?;
+                let val = self.ecx.retag_reference(val, mutbl)?;
+                self.ecx.write_immediate(val, place.into())?;
                 Ok(())
             }
         }

tests/compile-fail-fullmir/stacked_borrows/box_exclusive_violation1.rs

@@ -0,0 +1,29 @@
+fn demo_mut_advanced_unique(mut our: Box<i32>) -> i32 {
+  unknown_code_1(&*our);
+
+  // This "re-asserts" uniqueness of the reference: After writing, we know
+  // our tag is at the top of the stack.
+  *our = 5;
+
+  unknown_code_2();
+
+  // We know this will return 5
+  *our //~ ERROR does not exist on the stack
+}
+
+// Now comes the evil context
+use std::ptr;
+
+static mut LEAK: *mut i32 = ptr::null_mut();
+
+fn unknown_code_1(x: &i32) { unsafe {
+    LEAK = x as *const _ as *mut _;
+} }
+
+fn unknown_code_2() { unsafe {
+    *LEAK = 7;
+} }
+
+fn main() {
+    assert_eq!(demo_mut_advanced_unique(Box::new(0)), 5);
+}