[PATCH v4 2/3] fbcon: Rebuild rotated font buffer on font change
flat view
WARM1d
SUPERSEDED
From: Yao Yiqi <hidden>
Date: 2026-10-19 09:02:26
Also in:
dri-devel, lkml, stable
Subsystem:
framebuffer console, framebuffer core, framebuffer layer, the rest · Maintainers:
Helge Deller, Thomas Zimmermann, Simona Vetter, Linus Torvalds
Revision v4 of 3 in this series.
Revisions (3)
- v2 [diff vs current]
- v4 current
- v5 [diff vs current]
From: Yao Yiqi <redacted>
fbcon_rotate_font() caches a rotated copy of the console font in
par->rotated.buf. The buffer is sized from the font's width, height
and charcount, and is rebuilt in fbcon_init(), fbcon_switch() and
fbcon_modechanged(), but not in fbcon_do_set_font().
When the font is changed through KDFONTOP, the new geometry is
installed and vc_resize() redraws before the buffer is rebuilt. The
rotated putcs/cursor ops then index the old buffer with the new cell
size; KASAN reports a slab-out-of-bounds read in soft_cursor().
Rebuild the buffer for the visible console before the redraw, as the
other callers do: select the console's blitting state with
set_blitting_type() (which also uploads the new font's map on
tile-blitting hardware), then rebuild. Background consoles keep
their rebuild at fbcon_switch() time, as the buffer is shared per
framebuffer and must not be updated for a console that is not being
displayed.
Keep the old buffer out of the rebuild so that it can be restored if
vc_resize() fails: clear par->rotated.buf before calling
rotate_font(), which then allocates a fresh buffer. On failure,
err_out puts the old buffer back and re-selects the blitting state
so tile-blitting hardware gets the restored font's map; the font
change fails as a whole, and the error path never runs rotate_font()
again. The retry added by the next patch still covers
fbcon_switch() and fbcon_modechanged(), which cannot roll back.
Unlike the other callers, this one does not fall back to unrotated
rendering on failure: their "par->rotate = FB_ROTATE_UR;
set_blitting_type(vc, info);" pattern is ineffective, because
set_blitting_type() re-derives par->rotate from par->p->con_rotate.
Repairing that fallback is left to separate work.
Fixes: 6cc50e1c5b57 ("[PATCH] fbcon: Console Rotation - Add support to rotate font bitmap")
Cc: stable@vger.kernel.org
Signed-off-by: Yao Yiqi <redacted>
---
Changes in v4:
- Restore the saved rotated buffer on failure instead of re-running
rotate_font(), so that a second allocation failure cannot leave the
console in a third state.
- Keep the old buffer out of the rebuild by allocating a fresh one.
- Abort the font change when the rebuild fails.
- Guard the rotated state with CONFIG_FRAMEBUFFER_CONSOLE_ROTATION.
---
drivers/video/fbdev/core/fbcon.c | 50 ++++++++++++++++++++++++++++++++
1 file changed, 50 insertions(+)
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 01715873ea49..7605e4237ca5 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c@@ -2414,6 +2414,11 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount, font_data_t *old_fontdata = p->fontdata; const u8 *old_data = vc->vc_font.data; unsigned short old_hi_font_mask = vc->vc_hi_font_mask; +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION + u8 *saved_rotated_buf = NULL; + size_t saved_rotated_bufsize = 0; + bool rotated_saved = false; +#endif font_data_get(data);
@@ -2432,6 +2437,29 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount, else if (!vc->vc_hi_font_mask && charcount == 512) set_vc_hi_font(vc, true); + /* + * Select the console's blitting state and update par->rotated to + * match the new font, so that the rendering below does not use a + * cache that was built for the old font. Clear the buffer so the + * rebuild allocates a fresh one; the old buffer is kept until the + * font change can no longer fail. + */ + if (con_is_visible(vc)) { + set_blitting_type(vc, info); + if (par->bitops->rotate_font) { +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION + saved_rotated_buf = par->rotated.buf; + saved_rotated_bufsize = par->rotated.bufsize; + par->rotated.buf = NULL; + par->rotated.bufsize = 0; + rotated_saved = true; +#endif + ret = par->bitops->rotate_font(info, vc); + if (ret) + goto err_out; + } + } + if (resize) { int cols, rows;
@@ -2448,12 +2476,27 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount, update_screen(vc); } +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION + if (rotated_saved) + kfree(saved_rotated_buf); +#endif if (old_fontdata) font_data_put(old_fontdata); return 0; err_out: +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION + /* + * Drop the buffer built for the new font and restore the saved + * one. + */ + if (rotated_saved) { + kfree(par->rotated.buf); + par->rotated.buf = saved_rotated_buf; + par->rotated.bufsize = saved_rotated_bufsize; + } +#endif p->fontdata = old_fontdata; vc->vc_font.data = old_data; vc->vc_font.width = old_width;
@@ -2466,6 +2509,13 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount, else if (!old_hi_font_mask && vc->vc_hi_font_mask) set_vc_hi_font(vc, false); + /* + * Re-select the blitting type, which re-uploads the font map on + * tile-blitting hardware. + */ + if (con_is_visible(vc)) + set_blitting_type(vc, info); + font_data_put(data); return ret;
--
2.56.0