linux-kernel - [PATCH 1/2] Fonts: Support FONT_EXTRA_WORDS macros for font

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Message-Id: <926453876c92caac34cba8545716a491754d04d5.1603037079.git.yepeilin.cs@gmail.com>
Date:   Sun, 18 Oct 2020 14:12:04 -0400
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Daniel Vetter <daniel@...ll.ch>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Sven Schneider <s.schneider@...ona-technologies.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peilin Ye <yepeilin.cs@...il.com>
Subject: [PATCH 1/2] Fonts: Support FONT_EXTRA_WORDS macros for font_6x8

Recently, in commit 6735b4632def ("Fonts: Support FONT_EXTRA_WORDS macros
for built-in fonts"), we wrapped each of our built-in data buffers in a
`font_data` structure, in order to use the following macros on them, see
include/linux/font.h:

	#define REFCOUNT(fd)	(((int *)(fd))[-1])
	#define FNTSIZE(fd)	(((int *)(fd))[-2])
	#define FNTCHARCNT(fd)	(((int *)(fd))[-3])
	#define FNTSUM(fd)	(((int *)(fd))[-4])

	#define FONT_EXTRA_WORDS 4

Do the same thing to our new 6x8 font. For built-in fonts, currently we
only use FNTSIZE(). Since this is only a temporary solution for an
out-of-bounds issue in the framebuffer layer (see commit 5af08640795b
("fbcon: Fix global-out-of-bounds read in fbcon_get_font()")), all the
three other fields are intentionally set to zero in order to discourage
using these negative-indexing macros.

Signed-off-by: Peilin Ye <yepeilin.cs@...il.com>
---
 lib/fonts/font_6x8.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/fonts/font_6x8.c b/lib/fonts/font_6x8.c
index e06447788418..700039a9ceae 100644
--- a/lib/fonts/font_6x8.c
+++ b/lib/fonts/font_6x8.c
@@ -3,8 +3,8 @@
 
 #define FONTDATAMAX 2048
 
-static const unsigned char fontdata_6x8[FONTDATAMAX] = {
-
+static struct font_data fontdata_6x8 = {
+	{ 0, 0, FONTDATAMAX, 0 }, {
 	/* 0 0x00 '^@' */
 	0x00, /* 000000 */
 	0x00, /* 000000 */
@@ -2564,13 +2564,13 @@ static const unsigned char fontdata_6x8[FONTDATAMAX] = {
 	0x00, /* 000000 */
 	0x00, /* 000000 */
 	0x00, /* 000000 */
-};
+} };
 
 const struct font_desc font_6x8 = {
 	.idx	= FONT6x8_IDX,
 	.name	= "6x8",
 	.width	= 6,
 	.height	= 8,
-	.data	= fontdata_6x8,
+	.data	= fontdata_6x8.data,
 	.pref	= 0,
 };
-- 
2.25.1