[Harmony proxies] Non-configurable properties: fixed properties VS trap all with invariants enforcement

David Bruant david.bruant at labri.fr
Mon Jun 20 08:15:04 PDT 2011


Hi,

We may need to switch from the (bicephal) fixed properties model to a 
"trap all with invariants enforcement" model.

With the current simple membrane example:
-----
var o = {};
var s = makeSimpleMembrane(o);
var wrapper = s.wrapper,
     gate = s.gate;

// ... later, in untrusted code (variable name kept for readability)
Object.defineProperty(wrapper, 'a', {value:1, configurable:false});


// ... later, back in trusted code:
gate.disable()


// ... later in the same untrusted code which had a reference to the 
wrapper object.
wrapper.a; // 1 in the fixed properties model
// throw if the 'get' traps was actually called.
// Such a difference is certainly noticeable in all traps.
-----

The problem with the fixed property model is that properties exist on 
the proxy object itself with no way to control (and prevent in our case) 
access to them.

David


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