serial: 8250: Validate reg addr for Au1x00/RT288x i/o accessors

Au1x00/RT2800+ hardware has an alternate register layout which is
remapped with lookup tables by the au_serial_in()/out() i/o accessors.
However, the h/w does not support the complete 8250 register set, and
accesses to unmapped registers cause out-of-bounds lookups. Further,
because the lookup tables are defined by designated initializers, the
tables may contain unmapped entries (although the current tables do not).

Declare fixed-size lookup tables with contiguous initialization for
the complete 8250 register map; unmapped registers are initialized to -1.
Validate the register index (ie., 'offset') is in the range [0, table size).
Return fixed value for unmapped register reads and ignore unmapped register
writes.

Reported-by: Mason <slash.tmp@free.fr>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Tested-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_core.c

@@ -358,34 +358,46 @@ static void default_serial_dl_write(struct uart_8250_port *up, int value)
 #if defined(CONFIG_MIPS_ALCHEMY) || defined(CONFIG_SERIAL_8250_RT288X)
 
 /* Au1x00/RT288x UART hardware has a weird register layout */
-static const u8 au_io_in_map[] = {
-	[UART_RX]  = 0,
-	[UART_IER] = 2,
-	[UART_IIR] = 3,
-	[UART_LCR] = 5,
-	[UART_MCR] = 6,
-	[UART_LSR] = 7,
-	[UART_MSR] = 8,
+static const s8 au_io_in_map[8] = {
+	 0,	/* UART_RX  */
+	 2,	/* UART_IER */
+	 3,	/* UART_IIR */
+	 5,	/* UART_LCR */
+	 6,	/* UART_MCR */
+	 7,	/* UART_LSR */
+	 8,	/* UART_MSR */
+	-1,	/* UART_SCR (unmapped) */
 };
 
-static const u8 au_io_out_map[] = {
-	[UART_TX]  = 1,
-	[UART_IER] = 2,
-	[UART_FCR] = 4,
-	[UART_LCR] = 5,
-	[UART_MCR] = 6,
+static const s8 au_io_out_map[8] = {
+	 1,	/* UART_TX  */
+	 2,	/* UART_IER */
+	 4,	/* UART_FCR */
+	 5,	/* UART_LCR */
+	 6,	/* UART_MCR */
+	-1,	/* UART_LSR (unmapped) */
+	-1,	/* UART_MSR (unmapped) */
+	-1,	/* UART_SCR (unmapped) */
 };
 
 static unsigned int au_serial_in(struct uart_port *p, int offset)
 {
-	offset = au_io_in_map[offset] << p->regshift;
-	return __raw_readl(p->membase + offset);
+	if (offset >= ARRAY_SIZE(au_io_in_map))
+		return UINT_MAX;
+	offset = au_io_in_map[offset];
+	if (offset < 0)
+		return UINT_MAX;
+	return __raw_readl(p->membase + (offset << p->regshift));
 }
 
 static void au_serial_out(struct uart_port *p, int offset, int value)
 {
-	offset = au_io_out_map[offset] << p->regshift;
-	__raw_writel(value, p->membase + offset);
+	if (offset >= ARRAY_SIZE(au_io_out_map))
+		return;
+	offset = au_io_out_map[offset];
+	if (offset < 0)
+		return;
+	__raw_writel(value, p->membase + (offset << p->regshift));
 }
 
 /* Au1x00 haven't got a standard divisor latch */