[PATCH 6.12 126/132] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup
STALE303d
REVIEWED: 7 (7M)
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: 2025-12-03 16:55:12
Also in:
amd-gfx, dri-devel, linux-patches, nouveau, stable
2 review trailers.
6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Thomas Zimmermann <tzimmermann@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@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@redhat.com> Acked-by: Alex Deucher <alexander.deucher@amd.com> Cc: dri-devel@lists.freedesktop.org Cc: nouveau@lists.freedesktop.org Cc: amd-gfx@lists.freedesktop.org Cc: linux-fbdev@vger.kernel.org Cc: <redacted> # v2.6.34+ Link: https://patch.msgid.link/20251105161549.98836-1-tzimmermann@suse.de Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@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; }