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

From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	 pmenzel@molgen.mpg.de
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: [PATCH] powerpc/legacy_serial: Fix UBSAN: array-index-out-of-bounds
Date: Sat,  8 May 2021 06:36:21 +0000 (UTC)	[thread overview]
Message-ID: <d5e3c8e66bad3725d7d48d0e45c4b7eb7c02631d.1620455671.git.christophe.leroy@csgroup.eu> (raw)

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>
---
 arch/powerpc/kernel/legacy_serial.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/legacy_serial.c b/arch/powerpc/kernel/legacy_serial.c
index 8b2c1a8553a0..1c2e09e1d59b 100644
--- a/arch/powerpc/kernel/legacy_serial.c
+++ b/arch/powerpc/kernel/legacy_serial.c
@@ -354,15 +354,12 @@ static void __init setup_legacy_serial_console(int console)
 	udbg_uart_setup(info->speed, info->clock);
 }
 
-static int __init ioremap_legacy_serial_console(void)
+static int __init do_ioremap_legacy_serial_console(int console)
 {
-	struct legacy_serial_info *info = &legacy_serial_infos[legacy_serial_console];
-	struct plat_serial8250_port *port = &legacy_serial_ports[legacy_serial_console];
+	struct legacy_serial_info *info = &legacy_serial_infos[console];
+	struct plat_serial8250_port *port = &legacy_serial_ports[console];
 	void __iomem *vaddr;
 
-	if (legacy_serial_console < 0)
-		return 0;
-
 	if (!info->early_addr)
 		return 0;
 
@@ -376,6 +373,13 @@ static int __init ioremap_legacy_serial_console(void)
 
 	return 0;
 }
+
+static int __init ioremap_legacy_serial_console(void)
+{
+	if (legacy_serial_console < 0)
+		return 0;
+	return do_ioremap_legacy_serial_console(legacy_serial_console);
+}
 early_initcall(ioremap_legacy_serial_console);
 
 /*
-- 
2.25.0

