Erase video memory on shutdown

Originally created by Tails on #5356 (Redmine)

Ways to recover video memory from a shutdown system do exist: https://hsmr.cc/palinopsia/. Hence, Tails should erase that memory on shutdown.

Talking with a friend of mine who used to work on video card drivers for X.org (slightly paraphrased, didn’t need to take you through the entire conversation):

<brutalchaos> MostAwesomeDude: is it possible to erase video ram for all types of video cards during shutdown?
<MostAwesomeDude> You can't clear the VRAM until the computer's off, because the BIOS will keep writing to it up until the last second.
<brutalchaos> Is there a way to flush the vram then?
<MostAwesomeDude> Basically, become root, find the PCI BAR where VRAM's mapped, and walk over it. There's a couple things called mmapw and mmapr that can help you; Google for them.

Another idea, maybe related to the previous (this isn’t really my strong point), is mapping all RAM, including video memory as virtual RAM and with the use of kfree in the kernel, writing all 0’s to it.

When this is fixed, the entry in the FAQ should be removed.

Related issues

• Related to #9099 (closed)