linux-stable.git/drivers/video/fbdev/core/fbcon.c, branch linux-5.17.y

fbcon: Consistently protect deferred_takeover with console_lock()

2022-06-09T08:25:19+00:00

[ Upstream commit 43553559121ca90965b572cf8a1d6d0fd618b449 ]

This shouldn't be a problem in practice since until we've actually
taken over the console there's nothing we've registered with the
console/vt subsystem, so the exit/unbind path that check this can't
do the wrong thing. But it's confusing, so fix it by moving it a tad
later.

Acked-by: Sam Ravnborg 
Signed-off-by: Daniel Vetter 
Cc: Daniel Vetter 
Cc: Du Cheng 
Cc: Tetsuo Handa 
Cc: Claudio Suarez 
Cc: Thomas Zimmermann 
Link: https://patchwork.freedesktop.org/patch/msgid/20220405210335.3434130-14-daniel.vetter@ffwll.ch
Signed-off-by: Sasha Levin

fbcon: Avoid 'cap' set but not used warning

2022-02-08T13:44:15+00:00

Fix this kernel test robot warning:

  drivers/video/fbdev/core/fbcon.c: In function 'fbcon_init':
  drivers/video/fbdev/core/fbcon.c:1028:6: warning: variable 'cap' set but not used [-Wunused-but-set-variable]

The cap variable is only used when CONFIG_FRAMEBUFFER_CONSOLE_LEGACY_ACCELERATION
is enabled. Drop the temporary variable and use info->flags instead.

Fixes: 87ab9f6b7417 ("Revert "fbcon: Disable accelerated scrolling")
Reported-by: kernel test robot 
Signed-off-by: Helge Deller 
Signed-off-by: Daniel Vetter 
Link: https://patchwork.freedesktop.org/patch/msgid/YgFB4xqI+As196FR@p100

fbcon: Add option to enable legacy hardware acceleration

2022-02-02T14:16:26+00:00

Add a config option CONFIG_FRAMEBUFFER_CONSOLE_LEGACY_ACCELERATION to
enable bitblt and fillrect hardware acceleration in the framebuffer
console. If disabled, such acceleration will not be used, even if it is
supported by the graphics hardware driver.

If you plan to use DRM as your main graphics output system, you should
disable this option since it will prevent compiling in code which isn't
used later on when DRM takes over.

For all other configurations, e.g. if none of your graphic cards support
DRM (yet), DRM isn't available for your architecture, or you can't be
sure that the graphic card in the target system will support DRM, you
most likely want to enable this option.

In the non-accelerated case (e.g. when DRM is used), the inlined
fb_scrollmode() function is hardcoded to return SCROLL_REDRAW and as such the
compiler is able to optimize much unneccesary code away.

In this v3 patch version I additionally changed the GETVYRES() and GETVXRES()
macros to take a pointer to the fbcon_display struct. This fixes the build when
console rotation is enabled and helps the compiler again to optimize out code.

Signed-off-by: Helge Deller 
Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Helge Deller 
Signed-off-by: Daniel Vetter 
Link: https://patchwork.freedesktop.org/patch/msgid/20220202135531.92183-4-deller@gmx.de

Revert "fbcon: Disable accelerated scrolling"

2022-02-02T14:15:11+00:00

This reverts commit 39aead8373b3c20bb5965c024dfb51a94e526151.

Revert the first (of 2) commits which disabled scrolling acceleration in
fbcon/fbdev.  It introduced a regression for fbdev-supported graphic cards
because of the performance penalty by doing screen scrolling by software
instead of using the existing graphic card 2D hardware acceleration.

Console scrolling acceleration was disabled by dropping code which
checked at runtime the driver hardware capabilities for the
BINFO_HWACCEL_COPYAREA or FBINFO_HWACCEL_FILLRECT flags and if set, it
enabled scrollmode SCROLL_MOVE which uses hardware acceleration to move
screen contents.  After dropping those checks scrollmode was hard-wired
to SCROLL_REDRAW instead, which forces all graphic cards to redraw every
character at the new screen position when scrolling.

This change effectively disabled all hardware-based scrolling acceleration for
ALL drivers, because now all kind of 2D hardware acceleration (bitblt,
fillrect) in the drivers isn't used any longer.

The original commit message mentions that only 3 DRM drivers (nouveau, omapdrm
and gma500) used hardware acceleration in the past and thus code for checking
and using scrolling acceleration is obsolete.

This statement is NOT TRUE, because beside the DRM drivers there are around 35
other fbdev drivers which depend on fbdev/fbcon and still provide hardware
acceleration for fbdev/fbcon.

The original commit message also states that syzbot found lots of bugs in fbcon
and thus it's "often the solution to just delete code and remove features".
This is true, and the bugs - which actually affected all users of fbcon,
including DRM - were fixed, or code was dropped like e.g. the support for
software scrollback in vgacon (commit 973c096f6a85).

So to further analyze which bugs were found by syzbot, I've looked through all
patches in drivers/video which were tagged with syzbot or syzkaller back to
year 2005. The vast majority fixed the reported issues on a higher level, e.g.
when screen is to be resized, or when font size is to be changed. The few ones
which touched driver code fixed a real driver bug, e.g. by adding a check.

But NONE of those patches touched code of either the SCROLL_MOVE or the
SCROLL_REDRAW case.

That means, there was no real reason why SCROLL_MOVE had to be ripped-out and
just SCROLL_REDRAW had to be used instead. The only reason I can imagine so far
was that SCROLL_MOVE wasn't used by DRM and as such it was assumed that it
could go away. That argument completely missed the fact that SCROLL_MOVE is
still heavily used by fbdev (non-DRM) drivers.

Some people mention that using memcpy() instead of the hardware acceleration is
pretty much the same speed. But that's not true, at least not for older graphic
cards and machines where we see speed decreases by factor 10 and more and thus
this change leads to console responsiveness way worse than before.

That's why the original commit is to be reverted. By reverting we
reintroduce hardware-based scrolling acceleration and fix the
performance regression for fbdev drivers.

There isn't any impact on DRM when reverting those patches.

Signed-off-by: Helge Deller 
Acked-by: Geert Uytterhoeven 
Acked-by: Sven Schnelle 
Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Helge Deller 
Signed-off-by: Daniel Vetter 
Link: https://patchwork.freedesktop.org/patch/msgid/20220202135531.92183-3-deller@gmx.de

Revert "fbdev: Garbage collect fbdev scrolling acceleration, part 1 (from TODO list)"

2022-02-02T14:14:56+00:00

This reverts commit b3ec8cdf457e5e63d396fe1346cc788cf7c1b578.

Revert the second (of 2) commits which disabled scrolling acceleration
in fbcon/fbdev.  It introduced a regression for fbdev-supported graphic
cards because of the performance penalty by doing screen scrolling by
software instead of using the existing graphic card 2D hardware
acceleration.

Console scrolling acceleration was disabled by dropping code which
checked at runtime the driver hardware capabilities for the
BINFO_HWACCEL_COPYAREA or FBINFO_HWACCEL_FILLRECT flags and if set, it
enabled scrollmode SCROLL_MOVE which uses hardware acceleration to move
screen contents.  After dropping those checks scrollmode was hard-wired
to SCROLL_REDRAW instead, which forces all graphic cards to redraw every
character at the new screen position when scrolling.

This change effectively disabled all hardware-based scrolling acceleration for
ALL drivers, because now all kind of 2D hardware acceleration (bitblt,
fillrect) in the drivers isn't used any longer.

The original commit message mentions that only 3 DRM drivers (nouveau, omapdrm
and gma500) used hardware acceleration in the past and thus code for checking
and using scrolling acceleration is obsolete.

This statement is NOT TRUE, because beside the DRM drivers there are around 35
other fbdev drivers which depend on fbdev/fbcon and still provide hardware
acceleration for fbdev/fbcon.

The original commit message also states that syzbot found lots of bugs in fbcon
and thus it's "often the solution to just delete code and remove features".
This is true, and the bugs - which actually affected all users of fbcon,
including DRM - were fixed, or code was dropped like e.g. the support for
software scrollback in vgacon (commit 973c096f6a85).

So to further analyze which bugs were found by syzbot, I've looked through all
patches in drivers/video which were tagged with syzbot or syzkaller back to
year 2005. The vast majority fixed the reported issues on a higher level, e.g.
when screen is to be resized, or when font size is to be changed. The few ones
which touched driver code fixed a real driver bug, e.g. by adding a check.

But NONE of those patches touched code of either the SCROLL_MOVE or the
SCROLL_REDRAW case.

That means, there was no real reason why SCROLL_MOVE had to be ripped-out and
just SCROLL_REDRAW had to be used instead. The only reason I can imagine so far
was that SCROLL_MOVE wasn't used by DRM and as such it was assumed that it
could go away. That argument completely missed the fact that SCROLL_MOVE is
still heavily used by fbdev (non-DRM) drivers.

Some people mention that using memcpy() instead of the hardware acceleration is
pretty much the same speed. But that's not true, at least not for older graphic
cards and machines where we see speed decreases by factor 10 and more and thus
this change leads to console responsiveness way worse than before.

That's why the original commit is to be reverted. By reverting we
reintroduce hardware-based scrolling acceleration and fix the
performance regression for fbdev drivers.

There isn't any impact on DRM when reverting those patches.

Signed-off-by: Helge Deller 
Acked-by: Geert Uytterhoeven 
Acked-by: Sven Schnelle 
Cc: stable@vger.kernel.org # v5.16+
Signed-off-by: Helge Deller 
Signed-off-by: Daniel Vetter 
Link: https://patchwork.freedesktop.org/patch/msgid/20220202135531.92183-2-deller@gmx.de

fbdev: Garbage collect fbdev scrolling acceleration, part 1 (from TODO list)

2021-10-13T13:29:23+00:00

Scroll acceleration is disabled in fbcon by hard-wiring
p->scrollmode = SCROLL_REDRAW. Remove the obsolete code in fbcon.c
and fbdev/core/

Signed-off-by: Claudio Suarez 
Signed-off-by: Thomas Zimmermann 
Link: https://patchwork.freedesktop.org/patch/msgid/YVXTYqszZix9TxjJ@gineta.localdomain

tty: vt: always invoke vc->vc_sw->con_resize callback

2021-05-15T15:12:12+00:00

syzbot is reporting OOB write at vga16fb_imageblit() [1], for
resize_screen() from ioctl(VT_RESIZE) returns 0 without checking whether
requested rows/columns fit the amount of memory reserved for the graphical
screen if current mode is KD_GRAPHICS.

----------
  #include 
  #include 
  #include 
  #include 
  #include 
  #include 

  int main(int argc, char *argv[])
  {
        const int fd = open("/dev/char/4:1", O_RDWR);
        struct vt_sizes vt = { 0x4100, 2 };

        ioctl(fd, KDSETMODE, KD_GRAPHICS);
        ioctl(fd, VT_RESIZE, &vt);
        ioctl(fd, KDSETMODE, KD_TEXT);
        return 0;
  }
----------

Allow framebuffer drivers to return -EINVAL, by moving vc->vc_mode !=
KD_GRAPHICS check from resize_screen() to fbcon_resize().

Link: https://syzkaller.appspot.com/bug?extid=1f29e126cf461c4de3b3 [1]
Reported-by: syzbot 
Suggested-by: Linus Torvalds 
Signed-off-by: Tetsuo Handa 
Tested-by: syzbot 
Signed-off-by: Linus Torvalds

drivers: video: fbcon: fix NULL dereference in fbcon_cursor()

2021-03-23T14:15:17+00:00

add null-check on function pointer before dereference on ops->cursor

Reported-by: syzbot+b67aaae8d3a927f68d20@syzkaller.appspotmail.com
Cc: stable 
Signed-off-by: Du Cheng 
Link: https://lore.kernel.org/r/20210312081421.452405-1-ducheng2@gmail.com
Signed-off-by: Greg Kroah-Hartman

video: fbcon: Fix warnings by using pr_debug() in fbcon

2020-11-29T21:44:48+00:00

Replacing DPRINTK() statements with pr_debug fixes set but not used
warnings.  And moves to a more standard logging setup at the same time.

v2:
  - Fix indent (Joe)

Signed-off-by: Sam Ravnborg 
Acked-by: Thomas Zimmermann 
Cc: Joe Perches 
Cc: Greg Kroah-Hartman 
Cc: Daniel Vetter 
Cc: Bartlomiej Zolnierkiewicz 
Cc: Sam Ravnborg 
Cc: Jiri Slaby 
Cc: Peilin Ye 
Cc: Tetsuo Handa 
Cc: George Kennedy 
Cc: Nathan Chancellor 
Cc: Peter Rosin 
Link: https://patchwork.freedesktop.org/patch/msgid/20201128224114.1033617-3-sam@ravnborg.org

fbcon: Disable accelerated scrolling

2020-11-17T10:00:29+00:00

So ever since syzbot discovered fbcon, we have solid proof that it's
full of bugs. And often the solution is to just delete code and remove
features, e.g.  50145474f6ef ("fbcon: remove soft scrollback code").

Now the problem is that most modern-ish drivers really only treat
fbcon as an dumb kernel console until userspace takes over, and Oops
printer for some emergencies. Looking at drm drivers and the basic
vesa/efi fbdev drivers shows that only 3 drivers support any kind of
acceleration:

- nouveau, seems to be enabled by default
- omapdrm, when a DMM remapper exists using remapper rewriting for
  y/xpanning
- gma500, but that is getting deleted now for the GTT remapper trick,
  and the accelerated copyarea never set the FBINFO_HWACCEL_COPYAREA
  flag, so unused (and could be deleted already I think).

No other driver supportes accelerated fbcon. And fbcon is the only
user of this accel code (it's not exposed as uapi through ioctls),
which means we could garbage collect fairly enormous amounts of code
if we kill this.

Plus because syzbot only runs on virtual hardware, and none of the
drivers for that have acceleration, we'd remove a huge gap in testing.
And there's no other even remotely comprehensive testing aside from
syzbot.

This patch here just disables the acceleration code by always
redrawing when scrolling. The plan is that once this has been merged
for well over a year in released kernels, we can start to go around
and delete a lot of code.

v2:
- Drop a few more unused local variables, somehow I missed the
compiler warnings (Sam)
- Fix typo in comment (Jiri)
- add a todo entry for the cleanup (Thomas)

v3: Remove more unused variables (0day)

Reviewed-by: Tomi Valkeinen 
Reviewed-by: Thomas Zimmermann 
Reviewed-by: Greg Kroah-Hartman 
Acked-by: Sam Ravnborg 
Cc: Jiri Slaby 
Cc: Bartlomiej Zolnierkiewicz 
Cc: Greg Kroah-Hartman 
Cc: Linus Torvalds 
Cc: Ben Skeggs 
Cc: nouveau@lists.freedesktop.org
Cc: Tomi Valkeinen 
Cc: Daniel Vetter 
Cc: Jiri Slaby 
Cc: "Gustavo A. R. Silva" 
Cc: Tetsuo Handa 
Cc: Peilin Ye 
Cc: George Kennedy 
Cc: Nathan Chancellor 
Cc: Peter Rosin 
Signed-off-by: Daniel Vetter 
Link: https://patchwork.freedesktop.org/patch/msgid/20201029132229.4068359-1-daniel.vetter@ffwll.ch