fbdev: Prevent probing generic drivers if a FB is already registered

commit fb561bf9abde49f7e00fdbf9ed2ccf2d86cac8ee upstream.

The efifb and simplefb drivers just render to a pre-allocated frame buffer
and rely on the display hardware being initialized before the kernel boots.

But if another driver already probed correctly and registered a fbdev, the
generic drivers shouldn't be probed since an actual driver for the display
hardware is already present.

This is more likely to occur after commit d391c5827107 ("drivers/firmware:
move x86 Generic System Framebuffers support") since the "efi-framebuffer"
and "simple-framebuffer" platform devices are registered at a later time.

Link: https://lore.kernel.org/r/20211110200253.rfudkt3edbd3nsyj@lahvuun/
Fixes: d391c5827107 ("drivers/firmware: move x86 Generic System Framebuffers support")
Reported-by: Ilya Trukhanov <lahvuun@gmail.com>
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Tested-by: Ilya Trukhanov <lahvuun@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211111115757.1351045-1-javierm@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c
index edca370..ea42ba6 100644 (file)
--- a/drivers/video/fbdev/efifb.c
+++ b/drivers/video/fbdev/efifb.c
@@ -351,6 +351,17 @@ static int efifb_probe(struct platform_device *dev)
        char *option = NULL;
        efi_memory_desc_t md;
 
+       /*
+        * Generic drivers must not be registered if a framebuffer exists.
+        * If a native driver was probed, the display hardware was already
+        * taken and attempting to use the system framebuffer is dangerous.
+        */
+       if (num_registered_fb > 0) {
+               dev_err(&dev->dev,
+                       "efifb: a framebuffer is already registered\n");
+               return -EINVAL;
+       }
+
        if (screen_info.orig_video_isVGA != VIDEO_TYPE_EFI || pci_dev_disabled)
                return -ENODEV;
 

diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c
index 62f0ded..b63074f 100644 (file)
--- a/drivers/video/fbdev/simplefb.c
+++ b/drivers/video/fbdev/simplefb.c
@@ -407,6 +407,17 @@ static int simplefb_probe(struct platform_device *pdev)
        struct simplefb_par *par;
        struct resource *mem;
 
+       /*
+        * Generic drivers must not be registered if a framebuffer exists.
+        * If a native driver was probed, the display hardware was already
+        * taken and attempting to use the system framebuffer is dangerous.
+        */
+       if (num_registered_fb > 0) {
+               dev_err(&pdev->dev,
+                       "simplefb: a framebuffer is already registered\n");
+               return -EINVAL;
+       }
+
        if (fb_get_options("simplefb", NULL))
                return -ENODEV;