fbcon: remove soft scrollback code

mainline inclusion
from mainline-v5.9
commit 50145474
category: bugfix
bugzilla: NA
CVE: CVE-2020-14390

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

This (and the VGA soft scrollback) turns out to have various nasty small
special cases that nobody really is willing to fight.  The soft
scrollback code was really useful a few decades ago when you typically
used the console interactively as the main way to interact with the
machine, but that just isn't the case any more.

So it's not worth dragging along.
Tested-by: NYuan Ming <yuanmingbuaa@gmail.com>
Tested-by: NWilly Tarreau <w@1wt.eu>
Acked-by: NBartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/video/fbdev/core/fbcon.c

@@ -102,12 +102,6 @@ static int logo_lines;
 /* logo_shown is an index to vc_cons when >= 0; otherwise follows FBCON_LOGO
    enums.  */
 static int logo_shown = FBCON_LOGO_CANSHOW;
-/* Software scrollback */
-static int fbcon_softback_size = 32768;
-static unsigned long softback_buf, softback_curr;
-static unsigned long softback_in;
-static unsigned long softback_top, softback_end;
-static int softback_lines;
 /* console mappings */
 static int first_fb_vc;
 static int last_fb_vc = MAX_NR_CONSOLES - 1;
@@ -148,8 +142,6 @@ static int margin_color;
 
 static const struct consw fb_con;
 
-#define CM_SOFTBACK	(8)
-
 #define advance_row(p, delta) (unsigned short *)((unsigned long)(p) + (delta) * vc->vc_size_row)
 
 static int fbcon_set_origin(struct vc_data *);
@@ -355,18 +347,6 @@ static int get_color(struct vc_data *vc, struct fb_info *info,
 	return color;
 }
 
-static void fbcon_update_softback(struct vc_data *vc)
-{
-	int l = fbcon_softback_size / vc->vc_size_row;
-
-	if (l > 5)
-		softback_end = softback_buf + l * vc->vc_size_row;
-	else
-		/* Smaller scrollback makes no sense, and 0 would screw
-		   the operation totally */
-		softback_top = 0;
-}
-
 static void fb_flashcursor(struct work_struct *work)
 {
 	struct fb_info *info = container_of(work, struct fb_info, queue);
@@ -396,7 +376,7 @@ static void fb_flashcursor(struct work_struct *work)
 	c = scr_readw((u16 *) vc->vc_pos);
 	mode = (!ops->cursor_flash || ops->cursor_state.enable) ?
 		CM_ERASE : CM_DRAW;
-	ops->cursor(vc, info, mode, softback_lines, get_color(vc, info, c, 1),
+	ops->cursor(vc, info, mode, 0, get_color(vc, info, c, 1),
 		    get_color(vc, info, c, 0));
 	console_unlock();
 }
@@ -453,13 +433,7 @@ static int __init fb_console_setup(char *this_opt)
 		}
 		
 		if (!strncmp(options, "scrollback:", 11)) {
-			options += 11;
-			if (*options) {
-				fbcon_softback_size = simple_strtoul(options, &options, 0);
-				if (*options == 'k' || *options == 'K') {
-					fbcon_softback_size *= 1024;
-				}
-			}
+			pr_warn("Ignoring scrollback size option\n");
 			continue;
 		}
 		
@@ -988,31 +962,6 @@ static const char *fbcon_startup(void)
 
 	set_blitting_type(vc, info);
 
-	if (info->fix.type != FB_TYPE_TEXT) {
-		if (fbcon_softback_size) {
-			if (!softback_buf) {
-				softback_buf =
-				    (unsigned long)
-				    kmalloc(fbcon_softback_size,
-					    GFP_KERNEL);
-				if (!softback_buf) {
-					fbcon_softback_size = 0;
-					softback_top = 0;
-				}
-			}
-		} else {
-			if (softback_buf) {
-				kfree((void *) softback_buf);
-				softback_buf = 0;
-				softback_top = 0;
-			}
-		}
-		if (softback_buf)
-			softback_in = softback_top = softback_curr =
-			    softback_buf;
-		softback_lines = 0;
-	}
-
 	/* Setup default font */
 	if (!p->fontdata && !vc->vc_font.data) {
 		if (!fontname[0] || !(font = find_font(fontname)))
@@ -1181,9 +1130,6 @@ static void fbcon_init(struct vc_data *vc, int init)
 	if (logo)
 		fbcon_prepare_logo(vc, info, cols, rows, new_cols, new_rows);
 
-	if (vc == svc && softback_buf)
-		fbcon_update_softback(vc);
-
 	if (ops->rotate_font && ops->rotate_font(info, vc)) {
 		ops->rotate = FB_ROTATE_UR;
 		set_blitting_type(vc, info);
@@ -1346,7 +1292,6 @@ static void fbcon_cursor(struct vc_data *vc, int mode)
 {
 	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
 	struct fbcon_ops *ops = info->fbcon_par;
-	int y;
  	int c = scr_readw((u16 *) vc->vc_pos);
 
 	ops->cur_blink_jiffies = msecs_to_jiffies(vc->vc_cur_blink_ms);
@@ -1360,16 +1305,8 @@ static void fbcon_cursor(struct vc_data *vc, int mode)
 		fbcon_add_cursor_timer(info);
 
 	ops->cursor_flash = (mode == CM_ERASE) ? 0 : 1;
-	if (mode & CM_SOFTBACK) {
-		mode &= ~CM_SOFTBACK;
-		y = softback_lines;
-	} else {
-		if (softback_lines)
-			fbcon_set_origin(vc);
-		y = 0;
-	}
 
-	ops->cursor(vc, info, mode, y, get_color(vc, info, c, 1),
+	ops->cursor(vc, info, mode, 0, get_color(vc, info, c, 1),
 		    get_color(vc, info, c, 0));
 }
 
@@ -1440,8 +1377,6 @@ static void fbcon_set_disp(struct fb_info *info, struct fb_var_screeninfo *var,
 
 	if (con_is_visible(vc)) {
 		update_screen(vc);
-		if (softback_buf)
-			fbcon_update_softback(vc);
 	}
 }
 
@@ -1579,99 +1514,6 @@ static __inline__ void ypan_down_redraw(struct vc_data *vc, int t, int count)
 	scrollback_current = 0;
 }
 
-static void fbcon_redraw_softback(struct vc_data *vc, struct display *p,
-				  long delta)
-{
-	int count = vc->vc_rows;
-	unsigned short *d, *s;
-	unsigned long n;
-	int line = 0;
-
-	d = (u16 *) softback_curr;
-	if (d == (u16 *) softback_in)
-		d = (u16 *) vc->vc_origin;
-	n = softback_curr + delta * vc->vc_size_row;
-	softback_lines -= delta;
-	if (delta < 0) {
-		if (softback_curr < softback_top && n < softback_buf) {
-			n += softback_end - softback_buf;
-			if (n < softback_top) {
-				softback_lines -=
-				    (softback_top - n) / vc->vc_size_row;
-				n = softback_top;
-			}
-		} else if (softback_curr >= softback_top
-			   && n < softback_top) {
-			softback_lines -=
-			    (softback_top - n) / vc->vc_size_row;
-			n = softback_top;
-		}
-	} else {
-		if (softback_curr > softback_in && n >= softback_end) {
-			n += softback_buf - softback_end;
-			if (n > softback_in) {
-				n = softback_in;
-				softback_lines = 0;
-			}
-		} else if (softback_curr <= softback_in && n > softback_in) {
-			n = softback_in;
-			softback_lines = 0;
-		}
-	}
-	if (n == softback_curr)
-		return;
-	softback_curr = n;
-	s = (u16 *) softback_curr;
-	if (s == (u16 *) softback_in)
-		s = (u16 *) vc->vc_origin;
-	while (count--) {
-		unsigned short *start;
-		unsigned short *le;
-		unsigned short c;
-		int x = 0;
-		unsigned short attr = 1;
-
-		start = s;
-		le = advance_row(s, 1);
-		do {
-			c = scr_readw(s);
-			if (attr != (c & 0xff00)) {
-				attr = c & 0xff00;
-				if (s > start) {
-					fbcon_putcs(vc, start, s - start,
-						    line, x);
-					x += s - start;
-					start = s;
-				}
-			}
-			if (c == scr_readw(d)) {
-				if (s > start) {
-					fbcon_putcs(vc, start, s - start,
-						    line, x);
-					x += s - start + 1;
-					start = s + 1;
-				} else {
-					x++;
-					start++;
-				}
-			}
-			s++;
-			d++;
-		} while (s < le);
-		if (s > start)
-			fbcon_putcs(vc, start, s - start, line, x);
-		line++;
-		if (d == (u16 *) softback_end)
-			d = (u16 *) softback_buf;
-		if (d == (u16 *) softback_in)
-			d = (u16 *) vc->vc_origin;
-		if (s == (u16 *) softback_end)
-			s = (u16 *) softback_buf;
-		if (s == (u16 *) softback_in)
-			s = (u16 *) vc->vc_origin;
-	}
-}
-
 static void fbcon_redraw_move(struct vc_data *vc, struct display *p,
 			      int line, int count, int dy)
 {
@@ -1811,31 +1653,6 @@ static void fbcon_redraw(struct vc_data *vc, struct display *p,
 	}
 }
 
-static inline void fbcon_softback_note(struct vc_data *vc, int t,
-				       int count)
-{
-	unsigned short *p;
-
-	if (vc->vc_num != fg_console)
-		return;
-	p = (unsigned short *) (vc->vc_origin + t * vc->vc_size_row);
-
-	while (count) {
-		scr_memcpyw((u16 *) softback_in, p, vc->vc_size_row);
-		count--;
-		p = advance_row(p, 1);
-		softback_in += vc->vc_size_row;
-		if (softback_in == softback_end)
-			softback_in = softback_buf;
-		if (softback_in == softback_top) {
-			softback_top += vc->vc_size_row;
-			if (softback_top == softback_end)
-				softback_top = softback_buf;
-		}
-	}
-	softback_curr = softback_in;
-}
-
 static bool fbcon_scroll(struct vc_data *vc, unsigned int t, unsigned int b,
 		enum con_scroll dir, unsigned int count)
 {
@@ -1858,8 +1675,6 @@ static bool fbcon_scroll(struct vc_data *vc, unsigned int t, unsigned int b,
 	case SM_UP:
 		if (count > vc->vc_rows)	/* Maximum realistic size */
 			count = vc->vc_rows;
-		if (softback_top)
-			fbcon_softback_note(vc, t, count);
 		if (logo_shown >= 0)
 			goto redraw_up;
 		switch (p->scrollmode) {
@@ -2209,14 +2024,6 @@ static int fbcon_switch(struct vc_data *vc)
 	info = registered_fb[con2fb_map[vc->vc_num]];
 	ops = info->fbcon_par;
 
-	if (softback_top) {
-		if (softback_lines)
-			fbcon_set_origin(vc);
-		softback_top = softback_curr = softback_in = softback_buf;
-		softback_lines = 0;
-		fbcon_update_softback(vc);
-	}
-
 	if (logo_shown >= 0) {
 		struct vc_data *conp2 = vc_cons[logo_shown].d;
 
@@ -2550,9 +2357,6 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h,
 	int cnt;
 	char *old_data = NULL;
 
-	if (con_is_visible(vc) && softback_lines)
-		fbcon_set_origin(vc);
-
 	resize = (w != vc->vc_font.width) || (h != vc->vc_font.height);
 	if (p->userfont)
 		old_data = vc->vc_font.data;
@@ -2578,8 +2382,6 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h,
 		cols /= w;
 		rows /= h;
 		vc_resize(vc, cols, rows);
-		if (con_is_visible(vc) && softback_buf)
-			fbcon_update_softback(vc);
 	} else if (con_is_visible(vc)
 		   && vc->vc_mode == KD_TEXT) {
 		fbcon_clear_margins(vc, 0);
@@ -2738,19 +2540,7 @@ static void fbcon_set_palette(struct vc_data *vc, const unsigned char *table)
 
 static u16 *fbcon_screen_pos(struct vc_data *vc, int offset)
 {
-	unsigned long p;
-	int line;
-	
-	if (vc->vc_num != fg_console || !softback_lines)
-		return (u16 *) (vc->vc_origin + offset);
-	line = offset / vc->vc_size_row;
-	if (line >= softback_lines)
-		return (u16 *) (vc->vc_origin + offset -
-				softback_lines * vc->vc_size_row);
-	p = softback_curr + offset;
-	if (p >= softback_end)
-		p += softback_buf - softback_end;
-	return (u16 *) p;
+	return (u16 *) (vc->vc_origin + offset);
 }
 
 static unsigned long fbcon_getxy(struct vc_data *vc, unsigned long pos,
@@ -2764,22 +2554,7 @@ static unsigned long fbcon_getxy(struct vc_data *vc, unsigned long pos,
 
 		x = offset % vc->vc_cols;
 		y = offset / vc->vc_cols;
-		if (vc->vc_num == fg_console)
-			y += softback_lines;
 		ret = pos + (vc->vc_cols - x) * 2;
-	} else if (vc->vc_num == fg_console && softback_lines) {
-		unsigned long offset = pos - softback_curr;
-
-		if (pos < softback_curr)
-			offset += softback_end - softback_buf;
-		offset /= 2;
-		x = offset % vc->vc_cols;
-		y = offset / vc->vc_cols;
-		ret = pos + (vc->vc_cols - x) * 2;
-		if (ret == softback_end)
-			ret = softback_buf;
-		if (ret == softback_in)
-			ret = vc->vc_origin;
 	} else {
 		/* Should not happen */
 		x = y = 0;
@@ -2807,106 +2582,11 @@ static void fbcon_invert_region(struct vc_data *vc, u16 * p, int cnt)
 			a = ((a) & 0x88ff) | (((a) & 0x7000) >> 4) |
 			    (((a) & 0x0700) << 4);
 		scr_writew(a, p++);
-		if (p == (u16 *) softback_end)
-			p = (u16 *) softback_buf;
-		if (p == (u16 *) softback_in)
-			p = (u16 *) vc->vc_origin;
 	}
 }
 
-static void fbcon_scrolldelta(struct vc_data *vc, int lines)
-{
-	struct fb_info *info = registered_fb[con2fb_map[fg_console]];
-	struct fbcon_ops *ops = info->fbcon_par;
-	struct display *disp = &fb_display[fg_console];
-	int offset, limit, scrollback_old;
-
-	if (softback_top) {
-		if (vc->vc_num != fg_console)
-			return;
-		if (vc->vc_mode != KD_TEXT || !lines)
-			return;
-		if (logo_shown >= 0) {
-			struct vc_data *conp2 = vc_cons[logo_shown].d;
-
-			if (conp2->vc_top == logo_lines
-			    && conp2->vc_bottom == conp2->vc_rows)
-				conp2->vc_top = 0;
-			if (logo_shown == vc->vc_num) {
-				unsigned long p, q;
-				int i;
-
-				p = softback_in;
-				q = vc->vc_origin +
-				    logo_lines * vc->vc_size_row;
-				for (i = 0; i < logo_lines; i++) {
-					if (p == softback_top)
-						break;
-					if (p == softback_buf)
-						p = softback_end;
-					p -= vc->vc_size_row;
-					q -= vc->vc_size_row;
-					scr_memcpyw((u16 *) q, (u16 *) p,
-						    vc->vc_size_row);
-				}
-				softback_in = softback_curr = p;
-				update_region(vc, vc->vc_origin,
-					      logo_lines * vc->vc_cols);
-			}
-			logo_shown = FBCON_LOGO_CANSHOW;
-		}
-		fbcon_cursor(vc, CM_ERASE | CM_SOFTBACK);
-		fbcon_redraw_softback(vc, disp, lines);
-		fbcon_cursor(vc, CM_DRAW | CM_SOFTBACK);
-		return;
-	}
-
-	if (!scrollback_phys_max)
-		return;
-
-	scrollback_old = scrollback_current;
-	scrollback_current -= lines;
-	if (scrollback_current < 0)
-		scrollback_current = 0;
-	else if (scrollback_current > scrollback_max)
-		scrollback_current = scrollback_max;
-	if (scrollback_current == scrollback_old)
-		return;
-
-	if (fbcon_is_inactive(vc, info))
-		return;
-
-	fbcon_cursor(vc, CM_ERASE);
-
-	offset = disp->yscroll - scrollback_current;
-	limit = disp->vrows;
-	switch (disp->scrollmode) {
-	case SCROLL_WRAP_MOVE:
-		info->var.vmode |= FB_VMODE_YWRAP;
-		break;
-	case SCROLL_PAN_MOVE:
-	case SCROLL_PAN_REDRAW:
-		limit -= vc->vc_rows;
-		info->var.vmode &= ~FB_VMODE_YWRAP;
-		break;
-	}
-	if (offset < 0)
-		offset += limit;
-	else if (offset >= limit)
-		offset -= limit;
-
-	ops->var.xoffset = 0;
-	ops->var.yoffset = offset * vc->vc_font.height;
-	ops->update_start(info);
-
-	if (!scrollback_current)
-		fbcon_cursor(vc, CM_DRAW);
-}
-
 static int fbcon_set_origin(struct vc_data *vc)
 {
-	if (softback_lines)
-		fbcon_scrolldelta(vc, softback_lines);
 	return 0;
 }
 
@@ -2970,8 +2650,6 @@ static void fbcon_modechanged(struct fb_info *info)
 
 		fbcon_set_palette(vc, color_table);
 		update_screen(vc);
-		if (softback_buf)
-			fbcon_update_softback(vc);
 	}
 }
 
@@ -3413,7 +3091,6 @@ static const struct consw fb_con = {
 	.con_font_default	= fbcon_set_def_font,
 	.con_font_copy 		= fbcon_copy_font,
 	.con_set_palette 	= fbcon_set_palette,
-	.con_scrolldelta 	= fbcon_scrolldelta,
 	.con_set_origin 	= fbcon_set_origin,
 	.con_invert_region 	= fbcon_invert_region,
 	.con_screen_pos 	= fbcon_screen_pos,
@@ -3670,9 +3347,6 @@ static void fbcon_exit(void)
 	}
 #endif
 
-	kfree((void *)softback_buf);
-	softback_buf = 0UL;
-
 	for_each_registered_fb(i) {
 		int pending = 0;