NVIDIA has blamed Apple for an issue that can cause your private Mac activities to become exposed to other people who use your machine. It was initially thought that NVIDIA’s GPUs were the problem, but the chip maker says OS X’s memory management is the real culprit.
The apparent bug can sometimes cause a “ghost” of a previously closed window to be displayed briefly at a later time. This becomes a real issue if it displays private data to other users, such as confidential emails, or perhaps browsing habits you wouldn’t want others to see.
Even if you browse the web in incognito mode, a complete, pixel-for-pixel snapshot of your window can be reproduced. Many OS X users have reported this issue online, and it was thought that NVIDIA’s graphics chips were the problem.
“GPU memory is not erased before giving it to an application. This allows the contents of one application to leak into another,” explains University of Toronto engineering student Evan Andersen, who discovered the issue after browsing in Google Chrome’s incognito mode.
“When the Chrome incognito window was closed, its framebuffer was added to the pool of free GPU memory, but it was not erased. When Diablo requested a framebuffer of its own, Nvidia offered up the one previously used by Chrome.”
Since that framebuffer wasn’t erased, and Diablo didn’t clear it itself, a snapshot of Andersen’s Chrome window was displayed. Andersen then found a way to recreate the issue to ensure it wasn’t a rare occurrence before reporting it to NVIDIA and Google.
However, it turns out this isn’t an issue with NVIDIA’s graphics chips, or with Google Chrome — but rather a problem with OS X’s memory management system, according to NVIDIA. Other users have since reported the same problem with AMD graphics, too.
This issue should only be a concern to you if you share your Mac with other users, or frequently use it in public; no one can access these framebuffer snapshots remotely over a network, so unless they can see your screen in person, it’s not a problem.
Nevertheless, it’s something Apple needs to fix for those who do share Macs. As things stand, the company is yet to acknowledge the problem.
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