Microsoft Edge Chakra AsmJSByteCodeGenerator::EmitCall Call Handling

Microsoft Edge Chakra suffers from an AsmJSByteCodeGenerator::EmitCall call handling bug.

MD5 | 1c7860ec256452b1d95a1e70975c4a35

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


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.

function Module() {
'use asm';
function f() {

function g() {

var arr = [g];
return f;

let f = Module();

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

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