Commit 701d2054 authored by Thomas Zimmermann's avatar Thomas Zimmermann
Browse files

fbdev: Make support for userspace interfaces configurable 



Add Kconfig option CONFIG_FB_DEVICE and make the virtual fbdev
device optional. If the new option has not been selected, fbdev
does not create files in devfs, sysfs or procfs.

Most modern Linux systems run a DRM-based graphics stack that uses
the kernel's framebuffer console, but has otherwise deprecated fbdev
support. Yet fbdev userspace interfaces are still present.

The option makes it possible to use the fbdev subsystem as console
implementation without support for userspace. This closes potential
entry points to manipulate kernel or I/O memory via framebuffers. It
also prevents the execution of driver code via ioctl or sysfs, both
of which might allow malicious software to exploit bugs in the fbdev
code.

A small number of fbdev drivers require struct fbinfo.dev to be
initialized, usually for the support of sysfs interface. Make these
drivers depend on FB_DEVICE. They can later be fixed if necessary.

v3:
	* effect -> affect in Kconfig help (Daniel)
v2:
	* set FB_DEVICE default to y (Geert)
	* comment on {get,put}_device() (Sam)
	* Kconfig fixes (Sam)
	* add TODO item about FB_DEVICE dependencies (Sam)

Signed-off-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: default avatarSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613110953.24176-39-tzimmermann@suse.de
parent ff8fbcf6

Documentation/gpu/todo.rst

+13 −0
Original line number Diff line number Diff line
@@ -443,6 +443,19 @@ Contact: Thomas Zimmermann <tzimmermann@suse.de> 


Level: Starter



Remove driver dependencies on FB_DEVICE

---------------------------------------



A number of fbdev drivers provide attributes via sysfs and therefore depend

on CONFIG_FB_DEVICE to be selected. Review each driver and attempt to make

any dependencies on CONFIG_FB_DEVICE optional. At the minimum, the respective

code in the driver could be conditionalized via ifdef CONFIG_FB_DEVICE. Not

all drivers might be able to drop CONFIG_FB_DEVICE.



Contact: Thomas Zimmermann <tzimmermann@suse.de>



Level: Starter





Core refactorings

=================

drivers/staging/fbtft/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 
menuconfig FB_TFT

	tristate "Support for small TFT LCD display modules"

	depends on FB && SPI

	depends on FB_DEVICE

	depends on GPIOLIB || COMPILE_TEST

	select FB_SYS_FILLRECT

	select FB_SYS_COPYAREA

drivers/video/fbdev/Kconfig

+13 −0
Original line number Diff line number Diff line
@@ -57,6 +57,16 @@ config FIRMWARE_EDID 
	  combination with certain motherboards and monitors are known to

	  suffer from this problem.



config FB_DEVICE

	bool "Provide legacy /dev/fb* device"

	depends on FB

	default y

	help

	  Say Y here if you want the legacy /dev/fb* device file and

	  interfaces within sysfs anc procfs. It is only required if you

	  have userspace programs that depend on fbdev for graphics output.

	  This does not affect the framebuffer console. If unsure, say N.



config FB_DDC

	tristate

	depends on FB
@@ -1545,6 +1555,7 @@ config FB_3DFX_I2C 
config FB_VOODOO1

	tristate "3Dfx Voodoo Graphics (sst1) support"

	depends on FB && PCI

	depends on FB_DEVICE

	select FB_CFB_FILLRECT

	select FB_CFB_COPYAREA

	select FB_CFB_IMAGEBLIT
@@ -1862,6 +1873,7 @@ config FB_SH_MOBILE_LCDC 
	tristate "SuperH Mobile LCDC framebuffer support"

	depends on FB && HAVE_CLK && HAS_IOMEM

	depends on SUPERH || ARCH_RENESAS || COMPILE_TEST

	depends on FB_DEVICE

	select FB_SYS_FILLRECT

	select FB_SYS_COPYAREA

	select FB_SYS_IMAGEBLIT
@@ -1930,6 +1942,7 @@ config FB_SMSCUFX 
config FB_UDL

	tristate "Displaylink USB Framebuffer support"

	depends on FB && USB

	depends on FB_DEVICE

	select FB_MODE_HELPERS

	select FB_SYS_FILLRECT

	select FB_SYS_COPYAREA

drivers/video/fbdev/core/Makefile

+4 −3
Original line number Diff line number Diff line
@@ -2,12 +2,13 @@ 
obj-$(CONFIG_FB_NOTIFY)           += fb_notify.o

obj-$(CONFIG_FB)                  += fb.o

fb-y                              := fb_backlight.o \

                                     fb_chrdev.o \

                                     fb_info.o \

                                     fb_procfs.o \

                                     fbmem.o fbmon.o fbcmap.o fbsysfs.o \

                                     fbmem.o fbmon.o fbcmap.o \

                                     modedb.o fbcvt.o fb_cmdline.o fb_io_fops.o

fb-$(CONFIG_FB_DEFERRED_IO)       += fb_defio.o

fb-$(CONFIG_FB_DEVICE)            += fb_chrdev.o \

                                     fb_procfs.o \

                                     fbsysfs.o



ifeq ($(CONFIG_FRAMEBUFFER_CONSOLE),y)

fb-y				  += fbcon.o bitblit.o softcursor.o

drivers/video/fbdev/core/fb_internal.h

+38 −0
Original line number Diff line number Diff line
@@ -3,12 +3,22 @@ 
#ifndef _FB_INTERNAL_H

#define _FB_INTERNAL_H



#include <linux/device.h>

#include <linux/fb.h>

#include <linux/mutex.h>



/* fb_devfs.c */

#if defined(CONFIG_FB_DEVICE)

int fb_register_chrdev(void);

void fb_unregister_chrdev(void);

#else

static inline int fb_register_chrdev(void)

{

	return 0;

}

static inline void fb_unregister_chrdev(void)

{ }

#endif



/* fbmem.c */

extern struct class *fb_class;
@@ -19,11 +29,39 @@ struct fb_info *get_fb_info(unsigned int idx); 
void put_fb_info(struct fb_info *fb_info);



/* fb_procfs.c */

#if defined(CONFIG_FB_DEVICE)

int fb_init_procfs(void);

void fb_cleanup_procfs(void);

#else

static inline int fb_init_procfs(void)

{

	return 0;

}

static inline void fb_cleanup_procfs(void)

{ }

#endif



/* fbsysfs.c */

#if defined(CONFIG_FB_DEVICE)

int fb_device_create(struct fb_info *fb_info);

void fb_device_destroy(struct fb_info *fb_info);

#else

static inline int fb_device_create(struct fb_info *fb_info)

{

	/*

	 * Acquire a reference on the parent device to avoid

	 * unplug operations behind our back. With the fbdev

	 * device enabled, this is performed within register_device().

	 */

	get_device(fb_info->device);



	return 0;

}

static inline void fb_device_destroy(struct fb_info *fb_info)

{

	/* Undo the get_device() from fb_device_create() */

	put_device(fb_info->device);

}

#endif



#endif