Re: [kbd] [patchv2 3/3] VT: Bump font size limitation to 64x128 pixels

[Alexey Gladkov <legion@kernel.org>]

On Sun, Dec 18, 2022 at 01:32:12AM +0100, Samuel Thibault wrote:
> This moves 32x32 font size limitation checking down to drivers, so that
> fbcon can allow large fonts.
> 
> We still keep a limitation to 64x128 pixels so as to have a simple bounded
> allocation for con_font_get and in the userland kbd tool. That glyph size
> will however be enough to have 128x36 characters on a "16/9 8K display".
> 
> Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
> 
> ---
> V1 -> V2: Switch con_font_get to kvmalloc/kvfree instead of kmalloc/kfree
> 
> Index: linux-6.0/drivers/tty/vt/vt.c
> ===================================================================
> --- linux-6.0.orig/drivers/tty/vt/vt.c
> +++ linux-6.0/drivers/tty/vt/vt.c
> @@ -4575,17 +4575,20 @@ void reset_palette(struct vc_data *vc)
>  /*
>   *  Font switching
>   *
> - *  Currently we only support fonts up to 32 pixels wide, at a maximum height
> - *  of 32 pixels. Userspace fontdata is stored with 32 bytes (shorts/ints, 
> - *  depending on width) reserved for each character which is kinda wasty, but 
> - *  this is done in order to maintain compatibility with the EGA/VGA fonts. It 
> - *  is up to the actual low-level console-driver convert data into its favorite
> - *  format (maybe we should add a `fontoffset' field to the `display'
> - *  structure so we won't have to convert the fontdata all the time.
> + *  Currently we only support fonts up to 128 pixels wide, at a maximum height
> + *  of 128 pixels. Userspace fontdata may have to be stored with 32 bytes
> + *  (shorts/ints, depending on width) reserved for each character which is
> + *  kinda wasty, but this is done in order to maintain compatibility with the
> + *  EGA/VGA fonts. It is up to the actual low-level console-driver convert data
> + *  into its favorite format (maybe we should add a `fontoffset' field to the
> + *  `display' structure so we won't have to convert the fontdata all the time.
>   *  /Jes
>   */
>  
> -#define max_font_size 65536
> +#define max_font_width	64
> +#define max_font_height	128
> +#define max_font_glyphs	512
> +#define max_font_size	(max_font_glyphs*max_font_width*max_font_height)

As a suggestion that you can safely ignore. Maybe make max_font_glyphs a
sysctl parameter to be able to use larger fonts ?

I get requests from time to time in kbd that it is not possible to load a
larger font.

>  static int con_font_get(struct vc_data *vc, struct console_font_op *op)
>  {
> @@ -4595,7 +4598,7 @@ static int con_font_get(struct vc_data *
>  	unsigned int vpitch = op->op == KD_FONT_OP_GET_TALL ? op->height : 32;
>  
>  	if (op->data) {
> -		font.data = kmalloc(max_font_size, GFP_KERNEL);
> +		font.data = kvmalloc(max_font_size, GFP_KERNEL);
>  		if (!font.data)
>  			return -ENOMEM;
>  	} else
> @@ -4630,7 +4633,7 @@ static int con_font_get(struct vc_data *
>  		rc = -EFAULT;
>  
>  out:
> -	kfree(font.data);
> +	kvfree(font.data);
>  	return rc;
>  }
>  
> @@ -4645,9 +4648,10 @@ static int con_font_set(struct vc_data *
>  		return -EINVAL;
>  	if (!op->data)
>  		return -EINVAL;
> -	if (op->charcount > 512)
> +	if (op->charcount > max_font_glyphs)
>  		return -EINVAL;
> -	if (op->width <= 0 || op->width > 32 || !op->height || op->height > 32)
> +	if (op->width <= 0 || op->width > max_font_width || !op->height ||
> +	    op->height > max_font_height)
>  		return -EINVAL;
>  	if (vpitch < op->height)
>  		return -EINVAL;
> Index: linux-6.0/drivers/usb/misc/sisusbvga/sisusb_con.c
> ===================================================================
> --- linux-6.0.orig/drivers/usb/misc/sisusbvga/sisusb_con.c
> +++ linux-6.0/drivers/usb/misc/sisusbvga/sisusb_con.c
> @@ -1203,7 +1203,7 @@ sisusbcon_font_set(struct vc_data *c, st
>  	struct sisusb_usb_data *sisusb;
>  	unsigned charcount = font->charcount;
>  
> -	if (font->width != 8 || vpitch != 32 ||
> +	if (font->width != 8 || font->height > 32 || vpitch != 32 ||
>  	    (charcount != 256 && charcount != 512))
>  		return -EINVAL;
>  
> Index: linux-6.0/drivers/video/console/vgacon.c
> ===================================================================
> --- linux-6.0.orig/drivers/video/console/vgacon.c
> +++ linux-6.0/drivers/video/console/vgacon.c
> @@ -1037,7 +1037,7 @@ static int vgacon_font_set(struct vc_dat
>  	if (vga_video_type < VIDEO_TYPE_EGAM)
>  		return -EINVAL;
>  
> -	if (font->width != VGA_FONTWIDTH || vpitch != 32 ||
> +	if (font->width != VGA_FONTWIDTH || font->height > 32 || vpitch != 32 ||
>  	    (charcount != 256 && charcount != 512))
>  		return -EINVAL;
>  
> Index: linux-6.0/drivers/video/fbdev/core/fbcon.c
> ===================================================================
> --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
> +++ linux-6.0/drivers/video/fbdev/core/fbcon.c
> @@ -2279,6 +2279,8 @@ static int fbcon_get_font(struct vc_data
>  
>  	font->width = vc->vc_font.width;
>  	font->height = vc->vc_font.height;
> +	if (font->height > vpitch)
> +		return -ENOSPC;
>  	font->charcount = vc->vc_hi_font_mask ? 512 : 256;
>  	if (!font->data)
>  		return 0;
> 
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> 

-- 
Rgrds, legion