Greg Kroah-Hartman
2025-Dec-03 15:30 UTC
[PATCH 6.12 126/132] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup
6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Thomas Zimmermann <tzimmermann at suse.de>
[ Upstream commit eb76d0f5553575599561010f24c277cc5b31d003 ]
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: Sasha Levin <sashal at kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
drivers/gpu/drm/drm_fb_helper.c | 6 ------
drivers/gpu/drm/i915/display/intel_fbdev.c | 6 ------
drivers/gpu/drm/radeon/radeon_fbdev.c | 5 -----
drivers/video/fbdev/core/fbcon.c | 9 +++++++++
4 files changed, 9 insertions(+), 17 deletions(-)
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -30,9 +30,7 @@
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/console.h>
-#include <linux/pci.h>
#include <linux/sysrq.h>
-#include <linux/vga_switcheroo.h>
#include <drm/drm_atomic.h>
#include <drm/drm_drv.h>
@@ -1637,10 +1635,6 @@ static int drm_fb_helper_single_fb_probe
strcpy(fb_helper->fb->comm, "[fbcon]");
- /* Set the fb info for vgaswitcheroo clients. Does nothing otherwise. */
- if (dev_is_pci(dev->dev))
- vga_switcheroo_client_fb_set(to_pci_dev(dev->dev), fb_helper->info);
-
return 0;
}
--- a/drivers/gpu/drm/i915/display/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
@@ -589,11 +589,8 @@ static int intel_fbdev_restore_mode(stru
static void intel_fbdev_client_unregister(struct drm_client_dev *client)
{
struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client);
- struct drm_device *dev = fb_helper->dev;
- struct pci_dev *pdev = to_pci_dev(dev->dev);
if (fb_helper->info) {
- vga_switcheroo_client_fb_set(pdev, NULL);
drm_fb_helper_unregister_info(fb_helper);
} else {
drm_fb_helper_unprepare(fb_helper);
@@ -620,7 +617,6 @@ static int intel_fbdev_client_hotplug(st
{
struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client);
struct drm_device *dev = client->dev;
- struct pci_dev *pdev = to_pci_dev(dev->dev);
int ret;
if (dev->fb_helper)
@@ -634,8 +630,6 @@ static int intel_fbdev_client_hotplug(st
if (ret)
goto err_drm_fb_helper_fini;
- vga_switcheroo_client_fb_set(pdev, fb_helper->info);
-
return 0;
err_drm_fb_helper_fini:
--- a/drivers/gpu/drm/radeon/radeon_fbdev.c
+++ b/drivers/gpu/drm/radeon/radeon_fbdev.c
@@ -300,10 +300,8 @@ static void radeon_fbdev_client_unregist
{
struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client);
struct drm_device *dev = fb_helper->dev;
- struct radeon_device *rdev = dev->dev_private;
if (fb_helper->info) {
- vga_switcheroo_client_fb_set(rdev->pdev, NULL);
drm_helper_force_disable_all(dev);
drm_fb_helper_unregister_info(fb_helper);
} else {
@@ -325,7 +323,6 @@ static int radeon_fbdev_client_hotplug(s
{
struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client);
struct drm_device *dev = client->dev;
- struct radeon_device *rdev = dev->dev_private;
int ret;
if (dev->fb_helper)
@@ -342,8 +339,6 @@ static int radeon_fbdev_client_hotplug(s
if (ret)
goto err_drm_fb_helper_fini;
- vga_switcheroo_client_fb_set(rdev->pdev, fb_helper->info);
-
return 0;
err_drm_fb_helper_fini:
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -65,6 +65,7 @@
#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>
@@ -77,6 +78,7 @@
#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"
@@ -2894,6 +2896,9 @@ 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--;
@@ -3027,6 +3032,10 @@ 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;
}
Thomas Zimmermann
2025-Dec-03 17:15 UTC
[PATCH 6.12 126/132] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup
Hi, thank you for making the updated patch. Am 03.12.25 um 16:30 schrieb Greg Kroah-Hartman:> 6.12-stable review patch. If anyone has any objections, please let me know. > > ------------------ > > From: Thomas Zimmermann <tzimmermann at suse.de> > > [ Upstream commit eb76d0f5553575599561010f24c277cc5b31d003 ] > > 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: Sasha Levin <sashal at kernel.org> > Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>Reviewed-by: Thomas Zimmermann <tzimmermann at suse.de>> --- > drivers/gpu/drm/drm_fb_helper.c | 6 ------ > drivers/gpu/drm/i915/display/intel_fbdev.c | 6 ------ > drivers/gpu/drm/radeon/radeon_fbdev.c | 5 ----- > drivers/video/fbdev/core/fbcon.c | 9 +++++++++ > 4 files changed, 9 insertions(+), 17 deletions(-) > > --- a/drivers/gpu/drm/drm_fb_helper.c > +++ b/drivers/gpu/drm/drm_fb_helper.c > @@ -30,9 +30,7 @@ > #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt > > #include <linux/console.h> > -#include <linux/pci.h> > #include <linux/sysrq.h> > -#include <linux/vga_switcheroo.h> > > #include <drm/drm_atomic.h> > #include <drm/drm_drv.h> > @@ -1637,10 +1635,6 @@ static int drm_fb_helper_single_fb_probe > > strcpy(fb_helper->fb->comm, "[fbcon]"); > > - /* Set the fb info for vgaswitcheroo clients. Does nothing otherwise. */ > - if (dev_is_pci(dev->dev)) > - vga_switcheroo_client_fb_set(to_pci_dev(dev->dev), fb_helper->info); > - > return 0; > } > > --- a/drivers/gpu/drm/i915/display/intel_fbdev.c > +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c > @@ -589,11 +589,8 @@ static int intel_fbdev_restore_mode(stru > static void intel_fbdev_client_unregister(struct drm_client_dev *client) > { > struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client); > - struct drm_device *dev = fb_helper->dev; > - struct pci_dev *pdev = to_pci_dev(dev->dev); > > if (fb_helper->info) { > - vga_switcheroo_client_fb_set(pdev, NULL); > drm_fb_helper_unregister_info(fb_helper); > } else { > drm_fb_helper_unprepare(fb_helper); > @@ -620,7 +617,6 @@ static int intel_fbdev_client_hotplug(st > { > struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client); > struct drm_device *dev = client->dev; > - struct pci_dev *pdev = to_pci_dev(dev->dev); > int ret; > > if (dev->fb_helper) > @@ -634,8 +630,6 @@ static int intel_fbdev_client_hotplug(st > if (ret) > goto err_drm_fb_helper_fini; > > - vga_switcheroo_client_fb_set(pdev, fb_helper->info); > - > return 0; > > err_drm_fb_helper_fini: > --- a/drivers/gpu/drm/radeon/radeon_fbdev.c > +++ b/drivers/gpu/drm/radeon/radeon_fbdev.c > @@ -300,10 +300,8 @@ static void radeon_fbdev_client_unregist > { > struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client); > struct drm_device *dev = fb_helper->dev; > - struct radeon_device *rdev = dev->dev_private; > > if (fb_helper->info) { > - vga_switcheroo_client_fb_set(rdev->pdev, NULL); > drm_helper_force_disable_all(dev); > drm_fb_helper_unregister_info(fb_helper); > } else { > @@ -325,7 +323,6 @@ static int radeon_fbdev_client_hotplug(s > { > struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client); > struct drm_device *dev = client->dev; > - struct radeon_device *rdev = dev->dev_private; > int ret; > > if (dev->fb_helper) > @@ -342,8 +339,6 @@ static int radeon_fbdev_client_hotplug(s > if (ret) > goto err_drm_fb_helper_fini; > > - vga_switcheroo_client_fb_set(rdev->pdev, fb_helper->info); > - > return 0; > > err_drm_fb_helper_fini: > --- a/drivers/video/fbdev/core/fbcon.c > +++ b/drivers/video/fbdev/core/fbcon.c > @@ -65,6 +65,7 @@ > #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> > @@ -77,6 +78,7 @@ > #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" > @@ -2894,6 +2896,9 @@ 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--; > > @@ -3027,6 +3032,10 @@ 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; > } > > > >-- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 N?rnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG N?rnberg)