[PATCH V2] video/aperture: match the pci device when calling sysfb_disable()

[Alex Deucher <alexander.deucher@xxxxxxx>]

In aperture_remove_conflicting_pci_devices(), we currently only
call sysfb_disable() on vga class devices.  This leads to the
following problem when the pimary device is not VGA compatible:

1. A PCI device with a non-VGA class is the boot display
2. That device is probed first and it is not a VGA device so
   sysfb_disable() is not called, but the device resources
   are freed by aperture_detach_platform_device()
3. Non-primary GPU has a VGA class and it ends up calling sysfb_disable()
4. NULL pointer dereference via sysfb_disable() since the resources
   have already been freed by aperture_detach_platform_device() when
   it was called by the other device.

Fix this by passing a device pointer to sysfb_disable() and checking
the device to determine if we should execute it or not.

v2: Fix build when CONFIG_SCREEN_INFO is not set

Fixes: 5ae3716cfdcd ("video/aperture: Only remove sysfb on the default vga pci device")
Cc: Javier Martinez Canillas <javierm@xxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 drivers/firmware/sysfb.c | 11 +++++++++--
 drivers/of/platform.c    |  2 +-
 drivers/video/aperture.c |  5 ++---
 include/linux/sysfb.h    |  4 ++--
 4 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c
index 880ffcb500887..033a044af2646 100644
--- a/drivers/firmware/sysfb.c
+++ b/drivers/firmware/sysfb.c
@@ -39,6 +39,8 @@ static struct platform_device *pd;
 static DEFINE_MUTEX(disable_lock);
 static bool disabled;
 
+static struct device *sysfb_parent_dev(const struct screen_info *si);
+
 static bool sysfb_unregister(void)
 {
 	if (IS_ERR_OR_NULL(pd))
@@ -52,6 +54,7 @@ static bool sysfb_unregister(void)
 
 /**
  * sysfb_disable() - disable the Generic System Framebuffers support
+ * @dev:	the device to check if non-NULL
  *
  * This disables the registration of system framebuffer devices that match the
  * generic drivers that make use of the system framebuffer set up by firmware.
@@ -61,8 +64,12 @@ static bool sysfb_unregister(void)
  * Context: The function can sleep. A @disable_lock mutex is acquired to serialize
  *          against sysfb_init(), that registers a system framebuffer device.
  */
-void sysfb_disable(void)
+void sysfb_disable(struct device *dev)
 {
+	struct screen_info *si = &screen_info;
+
+	if (dev && dev != sysfb_parent_dev(si))
+		return;
 	mutex_lock(&disable_lock);
 	sysfb_unregister();
 	disabled = true;
@@ -93,7 +100,7 @@ static __init bool sysfb_pci_dev_is_enabled(struct pci_dev *pdev)
 }
 #endif
 
-static __init struct device *sysfb_parent_dev(const struct screen_info *si)
+static struct device *sysfb_parent_dev(const struct screen_info *si)
 {
 	struct pci_dev *pdev;
 
diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 389d4ea6bfc15..ef622d41eb5b2 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -592,7 +592,7 @@ static int __init of_platform_default_populate_init(void)
 			 * This can happen for example on DT systems that do EFI
 			 * booting and may provide a GOP handle to the EFI stub.
 			 */
-			sysfb_disable();
+			sysfb_disable(NULL);
 			of_platform_device_create(node, NULL, NULL);
 			of_node_put(node);
 		}
diff --git a/drivers/video/aperture.c b/drivers/video/aperture.c
index 561be8feca96c..b23d85ceea104 100644
--- a/drivers/video/aperture.c
+++ b/drivers/video/aperture.c
@@ -293,7 +293,7 @@ int aperture_remove_conflicting_devices(resource_size_t base, resource_size_t si
 	 * ask for this, so let's assume that a real driver for the display
 	 * was already probed and prevent sysfb to register devices later.
 	 */
-	sysfb_disable();
+	sysfb_disable(NULL);
 
 	aperture_detach_devices(base, size);
 
@@ -353,8 +353,7 @@ int aperture_remove_conflicting_pci_devices(struct pci_dev *pdev, const char *na
 	if (pdev == vga_default_device())
 		primary = true;
 
-	if (primary)
-		sysfb_disable();
+	sysfb_disable(&pdev->dev);
 
 	for (bar = 0; bar < PCI_STD_NUM_BARS; ++bar) {
 		if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h
index c9cb657dad08a..bef5f06a91de6 100644
--- a/include/linux/sysfb.h
+++ b/include/linux/sysfb.h
@@ -58,11 +58,11 @@ struct efifb_dmi_info {
 
 #ifdef CONFIG_SYSFB
 
-void sysfb_disable(void);
+void sysfb_disable(struct device *dev);
 
 #else /* CONFIG_SYSFB */
 
-static inline void sysfb_disable(void)
+static inline void sysfb_disable(struct device *dev)
 {
 }
 
-- 
2.46.0