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authorArnd Bergmann <arnd@arndb.de>2017-06-20 23:10:41 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-07-30 07:52:19 -0700
commit979990c6284814617d8f2179d197f72ff62b5d85 (patch)
treeb0d2c2be4776ec8e37896e2354bbf6858e6af6dc /drivers/tty/tty_buffer.c
parenta449f12bfe2f56c7975816d870c0bc0ef4d03125 (diff)
downloadlinux-979990c6284814617d8f2179d197f72ff62b5d85.tar.bz2
tty: improve tty_insert_flip_char() fast path
kernelci.org reports a crazy stack usage for the VT code when CONFIG_KASAN is enabled: drivers/tty/vt/keyboard.c: In function 'kbd_keycode': drivers/tty/vt/keyboard.c:1452:1: error: the frame size of 2240 bytes is larger than 2048 bytes [-Werror=frame-larger-than=] The problem is that tty_insert_flip_char() gets inlined many times into kbd_keycode(), and also into other functions, and each copy requires 128 bytes for stack redzone to check for a possible out-of-bounds access on the 'ch' and 'flags' arguments that are passed into tty_insert_flip_string_flags as a variable-length string. This introduces a new __tty_insert_flip_char() function for the slow path, which receives the two arguments by value. This completely avoids the problem and the stack usage goes back down to around 100 bytes. Without KASAN, this is also slightly better, as we don't have to spill the arguments to the stack but can simply pass 'ch' and 'flag' in registers, saving a few bytes in .text for each call site. This should be backported to linux-4.0 or later, which first introduced the stack sanitizer in the kernel. Cc: stable@vger.kernel.org Fixes: c420f167db8c ("kasan: enable stack instrumentation") Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/tty_buffer.c')
-rw-r--r--drivers/tty/tty_buffer.c24
1 files changed, 24 insertions, 0 deletions
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 4e7a4e9dcf4d..2da05fa37aec 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -362,6 +362,30 @@ int tty_insert_flip_string_flags(struct tty_port *port,
EXPORT_SYMBOL(tty_insert_flip_string_flags);
/**
+ * __tty_insert_flip_char - Add one character to the tty buffer
+ * @port: tty port
+ * @ch: character
+ * @flag: flag byte
+ *
+ * Queue a single byte to the tty buffering, with an optional flag.
+ * This is the slow path of tty_insert_flip_char.
+ */
+int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
+{
+ struct tty_buffer *tb = port->buf.tail;
+ int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
+
+ if (!tty_buffer_request_room(port, 1))
+ return 0;
+
+ *flag_buf_ptr(tb, tb->used) = flag;
+ *char_buf_ptr(tb, tb->used++) = ch;
+
+ return 1;
+}
+EXPORT_SYMBOL(__tty_insert_flip_char);
+
+/**
* tty_schedule_flip - push characters to ldisc
* @port: tty port to push from
*