ACPI: SPCR: Check for table version when using precise baudrate

commit 543d35004007a06ef247acf2fc55efa8388aa741 upstream.

Commit 4d330fe54145 ("ACPI: SPCR: Support Precise Baud Rate field")
added support to use the precise baud rate available since SPCR 1.09
(revision 4) but failed to check the version of the table provided by
the firmware.

Accessing an older version of SPCR table causes accesses beyond the
end of the table and can lead to garbage data to be used for the baud
rate.

Check the version of the firmware provided SPCR to ensure that the
precise baudrate is vaild before using it.

Fixes: 4d330fe54145 ("ACPI: SPCR: Support Precise Baud Rate field")
Signed-off-by: Punit Agrawal <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Rafael J. Wysocki <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Punit Agrawal

drivers/acpi/spcr.c

@@ -152,7 +152,7 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
 	 * Baud Rate field. If this field is zero or not present, Configured
 	 * Baud Rate is used.
 	 */
-	if (table->precise_baudrate)
+	if (table->header.revision >= 4 && table->precise_baudrate)
 		baud_rate = table->precise_baudrate;
 	else switch (table->baud_rate) {
 	case 0: