powerpc/legacy_serial: Fix UBSAN: array-index-out-of-bounds

UBSAN complains when a pointer is calculated with invalid
'legacy_serial_console' index, allthough the index is verified
before dereferencing the pointer.

Fix it by checking 'legacy_serial_console' validity before
calculating pointers.

Fixes: 0bd3f9e953bd ("powerpc/legacy_serial: Use early_ioremap()")
Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210511010712.750096-1-mpe@ellerman.id.au

diff --git a/arch/powerpc/kernel/legacy_serial.c b/arch/powerpc/kernel/legacy_serial.c
index 8b2c1a8..cfc03e0 100644 (file)
--- a/arch/powerpc/kernel/legacy_serial.c
+++ b/arch/powerpc/kernel/legacy_serial.c
@@ -356,13 +356,16 @@ static void __init setup_legacy_serial_console(int console)
 
 static int __init ioremap_legacy_serial_console(void)
 {
-       struct legacy_serial_info *info = &legacy_serial_infos[legacy_serial_console];
-       struct plat_serial8250_port *port = &legacy_serial_ports[legacy_serial_console];
+       struct plat_serial8250_port *port;
+       struct legacy_serial_info *info;
        void __iomem *vaddr;
 
        if (legacy_serial_console < 0)
                return 0;
 
+       info = &legacy_serial_infos[legacy_serial_console];
+       port = &legacy_serial_ports[legacy_serial_console];
+
        if (!info->early_addr)
                return 0;