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

[Alex Deucher]

I forgot to update the patch title but it should probably be something like:

video/aperture: optionally match the device in sysfb_disable()

Alex

On Mon, Aug 19, 2024 at 1:00 PM Alex Deucher <alexander.deucher at amd.com> wrote:
>
> 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 at redhat.com>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: Helge Deller <deller at gmx.de>
> Cc: Sam Ravnborg <sam at ravnborg.org>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
> Cc: stable at vger.kernel.org
> ---
>  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
>