On Wed, Nov 5, 2025 at 12:11 PM Thomas Zimmermann <[email protected]> wrote: > > 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 <[email protected]> > Link: > https://elixir.bootlin.com/linux/v6.17/source/drivers/video/fbdev/core/fbcon.c#L2942 > # [1]
I haven't paged switcheroo into my head in a while, but this seems to make sense so: Acked-by: Alex Deucher <[email protected]> > --- > drivers/gpu/drm/drm_fb_helper.c | 14 -------------- > drivers/video/fbdev/core/fbcon.c | 9 +++++++++ > 2 files changed, 9 insertions(+), 14 deletions(-) > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c > index 53e9dc0543de..c0343ec16a57 100644 > --- 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> > @@ -570,11 +568,6 @@ 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); > @@ -1614,7 +1607,6 @@ static int drm_fb_helper_single_fb_probe(struct > drm_fb_helper *fb_helper) > 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)) > @@ -1635,12 +1627,6 @@ static int drm_fb_helper_single_fb_probe(struct > drm_fb_helper *fb_helper) > > 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; > } > > diff --git a/drivers/video/fbdev/core/fbcon.c > b/drivers/video/fbdev/core/fbcon.c > index 7f35ad66b462..863944530c8e 100644 > --- 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" > @@ -2894,6 +2896,9 @@ void fbcon_fb_unregistered(struct fb_info *info) > > 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_info *info) > } > } > > + /* 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; > } > > -- > 2.51.1 >
