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(I have GNU/Linux and Microsoft Windows installed.) I played a game on Microsoft Windows, quit the game, restarted the PC, and selected GNU/Linux.

On the login screen, the background image was different, contorted, glitchy (similar to this image, but not as bad). On a closer look, it showed parts of the game I played … on the other OS, before the restart!
I could even "decrypt" some sentences, and various images were clearly recognizable (it might have been a sprite sheet, so technically only one image).

I guess this can be a privacy issue, especially because you’d typically expect that restarting and switching OS should "clear" traces like that (i.e., displayed content).

Is there someone at fault (software/OS or hardware)? Can you prevent this from happening somehow?

EDIT: It happened again (with a different game), and this time I made a photo:

GNU/Linux XFCE login screen shows image(s) from previous Windows session

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  • My comment is not helpful, but it is so strange what happened to you. I can not understand how come playing a game on Windows could be captured by Linux in anyway. How did you install the 2 OS (partitions/hard drives)?
    – user45139
    Jul 30, 2014 at 7:04
  • @begueradj: On different partitions of the same hard drive. After starting the PC, I select the OS in GRUB.
    – unor
    Jul 30, 2014 at 7:59
  • Most likely Linux didn't clear/paint to the buffer it got from the GPU, so you were left seeing whatever had previously been. In this case, it was data from when you had been in Windows. I've seen Linux do this countless times when resuming/switching VTs. Since what's in RAM isn't cleared on a reboot, it's not shocking this could occur from a different OS.
    – Kitsune
    Sep 20, 2014 at 17:09
  • The German IT news magazine heise online reports that someone created a proof of concept for (what seems to me) this issue: The Palinopsia Bug (also on Hacker News).
    – unor
    Mar 28, 2015 at 3:02

1 Answer 1

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This is almost certainly a hardware fault in the video card; it's possible (but unlikely) that it's a bug in the video driver instead. The scrambled image you're seeing is leftover data from the game, stored in the video card's memory. Since you rebooted rather than doing a cold shutdown, the data wasn't lost due to lack of power. On starting up, Linux asked the video card to use a certain part of its memory to display the screen and provided an image to display, but due to the aforementioned fault, the part of memory displayed was not the part the image was sent to; rather, old data from your game was displayed instead.

Yes, this is theoretically a security issue. In practice, it's rare enough that an attacker will use something more reliable instead, such as a cold boot attack.

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  • I see, thank you. Do you know if an OS could decide to clear this video card memory if the user wants to reboot? Or is it out of reach for operating systems? -- So unless this memory can be cleared, one should always do a cold shutdown instead of a reboot when switching users on the same PC (unless you don’t care about a possible privacy breach).
    – unor
    Sep 21, 2014 at 9:41
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    It's theoretically possible to wipe the video card memory during shutdown or startup, but I'm not aware of any OS that does it.
    – Mark
    Sep 21, 2014 at 10:01

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