vt: make the default color configurable

The virtual console has (undocumented) module parameters to set the
colors for italic and underlined text, but the default text color was
hardcoded for some reason.  This made it impossible to change the color
for startup messages, or to set the default for new virtual consoles.
Add a module parameter for that, and document the entire bunch.

Any hacker who thinks that a command prompt on a "black screen with
white font" is not supicious enough can now use the kernel parameter
vt.color=10 to get a nice, evil green.
Signed-off-by: NClemens Ladisch <clemens@ladisch.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/kernel-parameters.txt

@@ -3322,6 +3322,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			            them quite hard to use for exploits but
 			            might break your system.
 
+	vt.color=	[VT] Default text color.
+			Format: 0xYX, X = foreground, Y = background.
+			Default: 0x07 = light gray on black.
+
 	vt.cur_default=	[VT] Default cursor shape.
 			Format: 0xCCBBAA, where AA, BB, and CC are the same as
 			the parameters of the <Esc>[?A;B;Cc escape sequence;
@@ -3361,6 +3365,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			overridden by individual drivers. 0 will hide
 			cursors, 1 will display them.
 
+	vt.italic=	[VT] Default color for italic text; 0-15.
+			Default: 2 = green.
+
+	vt.underline=	[VT] Default color for underlined text; 0-15.
+			Default: 3 = cyan.
+
 	watchdog timers	[HW,WDT] For information on watchdog timers,
 			see Documentation/watchdog/watchdog-parameters.txt
 			or other driver-specific files in the

drivers/tty/vt/vt.c

@@ -2809,8 +2809,10 @@ static void con_shutdown(struct tty_struct *tty)
 	console_unlock();
 }
 
+static int default_color           = 7; /* white */
 static int default_italic_color    = 2; // green (ASCII)
 static int default_underline_color = 3; // cyan (ASCII)
+module_param_named(color, default_color, int, S_IRUGO | S_IWUSR);
 module_param_named(italic, default_italic_color, int, S_IRUGO | S_IWUSR);
 module_param_named(underline, default_underline_color, int, S_IRUGO | S_IWUSR);
 
@@ -2832,7 +2834,7 @@ static void vc_init(struct vc_data *vc, unsigned int rows,
 		vc->vc_palette[k++] = default_grn[j] ;
 		vc->vc_palette[k++] = default_blu[j] ;
 	}
-	vc->vc_def_color       = 0x07;   /* white */
+	vc->vc_def_color       = default_color;
 	vc->vc_ulcolor         = default_underline_color;
 	vc->vc_itcolor         = default_italic_color;
 	vc->vc_halfcolor       = 0x08;   /* grey */