linux-kernel - [PATCH 4.4 24/75] ARM: 8051/1: put_user: fix possible data corruption in put

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Date:   Fri,  8 Nov 2019 19:49:41 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrey Ryabinin <a.ryabinin@...sung.com>,
        Nicolas Pitre <nico@...aro.org>,
        Russell King <rmk+kernel@....linux.org.uk>,
        Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH 4.4 24/75] ARM: 8051/1: put_user: fix possible data corruption in put_user

From: Andrey Ryabinin <a.ryabinin@...sung.com>

Commit 537094b64b229bf3ad146042f83e74cf6abe59df upstream.

According to arm procedure call standart r2 register is call-cloberred.
So after the result of x expression was put into r2 any following
function call in p may overwrite r2. To fix this, the result of p
expression must be saved to the temporary variable before the
assigment x expression to __r2.

Signed-off-by: Andrey Ryabinin <a.ryabinin@...sung.com>
Reviewed-by: Nicolas Pitre <nico@...aro.org>
Cc: stable@...r.kernel.org
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm/include/asm/uaccess.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -251,7 +251,7 @@ extern int __put_user_8(void *, unsigned
 	({								\
 		unsigned long __limit = current_thread_info()->addr_limit - 1; \
 		const typeof(*(p)) __user *__tmp_p = (p);		\
-		register typeof(*(p)) __r2 asm("r2") = (x);	\
+		register const typeof(*(p)) __r2 asm("r2") = (x);	\
 		register const typeof(*(p)) __user *__p asm("r0") = __tmp_p; \
 		register unsigned long __l asm("r1") = __limit;		\
 		register int __e asm("r0");				\