linux-kernel - Privacy issue with blanking screensaver on 6.5+ kernel

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Message-ID: <ZZquFOfeEoU8cZ4F@ikki.ethgen.ch>
Date: Sun, 7 Jan 2024 14:58:44 +0100
From: Klaus Ethgen <Klaus+lkml@...gen.de>
To: linux-kernel@...r.kernel.org
Cc: Klaus+lkml@...gen.de
Subject: Privacy issue with blanking screensaver on 6.5+ kernel

Hi,

I have an privacy issue with kernel 6.5+ on AMD GPU.

I usually lock my laptop (AMD GPU) with xscreensaver in blank only mode.
Up to kernel 6.4, this is working perfect.

But since 6.5, sometimes after coming back from sleep, only the desktop
background is black but all windows fully visible. Of cause, I need to
unlock the screensaver to interact with the windows but they are visible
and might have confidential content.

I seen that issue also on a different Lenovo laptop.

There are the facts that I know:
- Kernel 6.5+, last kernel with positive identified bug: 6.6.9
- AMD GPU (I cannot say if other GPUs have the same issue, I only have
  this GPU with such a use pattern.
- Problem occurs after coming back from sleep but not always
- Desktop is fvwm (2 or 3, doesn't matter)
- Screensaver is xscreensaver version 6.06
- Display size is 1920x1200 but read below
- Output is eDP, internal Panel of the laptop (I cannot exclude
  different output as I don't have)

There is another issue in the early 6.5 series that is already fixed. My
laptop has a main resolution of 3840x2400 but this is far from readable.
It is impossible to see any on that resolution. That's why I use
1920x1200 on that display. In the early 6.5 series, the resolution of
1920x1200 was not available anymore, which led me to the idea, that
there was some rework in AMD based driver which has the regression of
the above rework.

About reproducing:
The issue does not happens every time the laptop comes back from sleep.
I have always to check for several days to see if the bug is still there
or not. But it seems that the issue happens more often after longer
sleep.

Regards
   Klaus

Ps. Please keep me in Cc as I am not subscribed to the list.
-- 
Klaus Ethgen                                       http://www.ethgen.ch/
pub  4096R/4E20AF1C 2011-05-16            Klaus Ethgen <Klaus@...gen.ch>
Fingerprint: 85D4 CA42 952C 949B 1753  62B3 79D0 B06F 4E20 AF1C

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