tty: improve tty_insert_flip_char() fast path (979990c6) · Commits · 戴 / test

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: ("kasan: enable stack instrumentation") Signed-off-by:

Arnd Bergmann <arnd@arndb.de> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_buffer.c

+24 −0

Original line number	Diff line number	Diff line
		@@ -361,6 +361,30 @@ 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

include/linux/tty_flip.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -12,6 +12,7 @@ extern int tty_prepare_flip_string(struct tty_port *port,
		unsigned char **chars, size_t size);
		extern void tty_flip_buffer_push(struct tty_port *port);
		void tty_schedule_flip(struct tty_port *port);
		int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag);

		static inline int tty_insert_flip_char(struct tty_port *port,
		unsigned char ch, char flag)
		@@ -26,7 +27,7 @@ static inline int tty_insert_flip_char(struct tty_port *port,
		*char_buf_ptr(tb, tb->used++) = ch;
		return 1;
		}
		return tty_insert_flip_string_flags(port, &ch, &flag, 1);
		return __tty_insert_flip_char(port, ch, flag);
		}

		static inline int tty_insert_flip_string(struct tty_port *port,

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