gregkh at linuxfoundation.org
2025-Dec-01 16:08 UTC
Patch "drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup" has been added to the 6.17-stable tree
This is a note to let you know that I've just added the patch titled
drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup
to the 6.17-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-fbcon-vga_switcheroo-avoid-race-condition-in-fbcon-setup.patch
and it can be found in the queue-6.17 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.
>From eb76d0f5553575599561010f24c277cc5b31d003 Mon Sep 17 00:00:00 2001
From: Thomas Zimmermann <tzimmermann at suse.de>
Date: Wed, 5 Nov 2025 17:14:49 +0100
Subject: drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup
From: Thomas Zimmermann <tzimmermann at suse.de>
commit eb76d0f5553575599561010f24c277cc5b31d003 upstream.
Protect vga_switcheroo_client_fb_set() with console lock. Avoids OOB
access in fbcon_remap_all(). Without holding the console lock the call
races with switching outputs.
VGA switcheroo calls fbcon_remap_all() when switching clients. The fbcon
function uses struct fb_info.node, which is set by register_framebuffer().
As the fb-helper code currently sets up VGA switcheroo before registering
the framebuffer, the value of node is -1 and therefore not a legal value.
For example, fbcon uses the value within set_con2fb_map() [1] as an index
into an array.
Moving vga_switcheroo_client_fb_set() after register_framebuffer() can
result in VGA switching that does not switch fbcon correctly.
Therefore move vga_switcheroo_client_fb_set() under fbcon_fb_registered(),
which already holds the console lock. Fbdev calls fbcon_fb_registered()
from within register_framebuffer(). Serializes the helper with VGA
switcheroo's call to fbcon_remap_all().
Although vga_switcheroo_client_fb_set() takes an instance of struct fb_info
as parameter, it really only needs the contained fbcon state. Moving the
call to fbcon initialization is therefore cleaner than before. Only amdgpu,
i915, nouveau and radeon support vga_switcheroo. For all other drivers,
this change does nothing.
Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Link:
https://elixir.bootlin.com/linux/v6.17/source/drivers/video/fbdev/core/fbcon.c#L2942
# [1]
Fixes: 6a9ee8af344e ("vga_switcheroo: initial implementation (v15)")
Acked-by: Javier Martinez Canillas <javierm at redhat.com>
Acked-by: Alex Deucher <alexander.deucher at amd.com>
Cc: dri-devel at lists.freedesktop.org
Cc: nouveau at lists.freedesktop.org
Cc: amd-gfx at lists.freedesktop.org
Cc: linux-fbdev at vger.kernel.org
Cc: <stable at vger.kernel.org> # v2.6.34+
Link: https://patch.msgid.link/20251105161549.98836-1-tzimmermann at suse.de
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
drivers/gpu/drm/drm_fb_helper.c | 14 --------------
drivers/video/fbdev/core/fbcon.c | 9 +++++++++
2 files changed, 9 insertions(+), 14 deletions(-)
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -31,9 +31,7 @@
#include <linux/console.h>
#include <linux/export.h>
-#include <linux/pci.h>
#include <linux/sysrq.h>
-#include <linux/vga_switcheroo.h>
#include <drm/drm_atomic.h>
#include <drm/drm_drv.h>
@@ -566,11 +564,6 @@ EXPORT_SYMBOL(drm_fb_helper_release_info
*/
void drm_fb_helper_unregister_info(struct drm_fb_helper *fb_helper)
{
- struct fb_info *info = fb_helper->info;
- struct device *dev = info->device;
-
- if (dev_is_pci(dev))
- vga_switcheroo_client_fb_set(to_pci_dev(dev), NULL);
unregister_framebuffer(fb_helper->info);
}
EXPORT_SYMBOL(drm_fb_helper_unregister_info);
@@ -1632,7 +1625,6 @@ static int drm_fb_helper_single_fb_probe
struct drm_client_dev *client = &fb_helper->client;
struct drm_device *dev = fb_helper->dev;
struct drm_fb_helper_surface_size sizes;
- struct fb_info *info;
int ret;
if (drm_WARN_ON(dev, !dev->driver->fbdev_probe))
@@ -1653,12 +1645,6 @@ static int drm_fb_helper_single_fb_probe
strcpy(fb_helper->fb->comm, "[fbcon]");
- info = fb_helper->info;
-
- /* Set the fb info for vgaswitcheroo clients. Does nothing otherwise. */
- if (dev_is_pci(info->device))
- vga_switcheroo_client_fb_set(to_pci_dev(info->device), info);
-
return 0;
}
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -66,6 +66,7 @@
#include <linux/string.h>
#include <linux/kd.h>
#include <linux/panic.h>
+#include <linux/pci.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/fb.h>
@@ -78,6 +79,7 @@
#include <linux/interrupt.h>
#include <linux/crc32.h> /* For counting font checksums */
#include <linux/uaccess.h>
+#include <linux/vga_switcheroo.h>
#include <asm/irq.h>
#include "fbcon.h"
@@ -2906,6 +2908,9 @@ void fbcon_fb_unregistered(struct fb_inf
console_lock();
+ if (info->device && dev_is_pci(info->device))
+ vga_switcheroo_client_fb_set(to_pci_dev(info->device), NULL);
+
fbcon_registered_fb[info->node] = NULL;
fbcon_num_registered_fb--;
@@ -3039,6 +3044,10 @@ static int do_fb_registered(struct fb_in
}
}
+ /* Set the fb info for vga_switcheroo clients. Does nothing otherwise. */
+ if (info->device && dev_is_pci(info->device))
+ vga_switcheroo_client_fb_set(to_pci_dev(info->device), info);
+
return ret;
}
Patches currently in stable-queue which might be from tzimmermann at suse.de are
queue-6.17/drm-fbcon-vga_switcheroo-avoid-race-condition-in-fbcon-setup.patch