releases/6.6.2/arm-9321-1-memset-cast-the-constant-byte-to-unsigned.patch

From bfed07efe398aa430716a7e88b1040b60ad06ec7 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Tue, 22 Aug 2023 15:06:06 +0100
Subject: ARM: 9321/1: memset: cast the constant byte to unsigned char

From: Kursad Oney <kursad.oney@broadcom.com>

[ Upstream commit c0e824661f443b8cab3897006c1bbc69fd0e7bc4 ]

memset() description in ISO/IEC 9899:1999 (and elsewhere) says:

	The memset function copies the value of c (converted to an
	unsigned char) into each of the first n characters of the
	object pointed to by s.

The kernel's arm32 memset does not cast c to unsigned char. This results
in the following code to produce erroneous output:

	char a[128];
	memset(a, -128, sizeof(a));

This is because gcc will generally emit the following code before
it calls memset() :

	mov   r0, r7
	mvn   r1, #127        ; 0x7f
	bl    00000000 <memset>

r1 ends up with 0xffffff80 before being used by memset() and the
'a' array will have -128 once in every four bytes while the other
bytes will be set incorrectly to -1 like this (printing the first
8 bytes) :

	test_module: -128 -1 -1 -1
	test_module: -1 -1 -1 -128

The change here is to 'and' r1 with 255 before it is used.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Kursad Oney <kursad.oney@broadcom.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/arm/lib/memset.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/lib/memset.S b/arch/arm/lib/memset.S
index d71ab61430b26..de75ae4d5ab41 100644
--- a/arch/arm/lib/memset.S
+++ b/arch/arm/lib/memset.S
@@ -17,6 +17,7 @@ ENTRY(__memset)
 ENTRY(mmioset)
 WEAK(memset)
 UNWIND( .fnstart         )
+	and	r1, r1, #255		@ cast to unsigned char
 	ands	r3, r0, #3		@ 1 unaligned?
 	mov	ip, r0			@ preserve r0 as return value
 	bne	6f			@ 1
-- 
2.42.0