linux-kernel - [PATCHv2] arm: put_user: fix possible data corruption in put

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Message-id: <1399360312-13843-1-git-send-email-a.ryabinin@samsung.com>
Date:	Tue, 06 May 2014 11:11:51 +0400
From:	Andrey Ryabinin <a.ryabinin@...sung.com>
To:	linux@....linux.org.uk
Cc:	Andrey Ryabinin <a.ryabinin@...sung.com>, stable@...r.kernel.org,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org (moderated list:ARM PORT),
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCHv2] arm: put_user: fix possible data corruption in put_user

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
---
Since v1:
 - tmp_p variable renamed to __tmp_p
 - added Reviewed-by tag
 - added Cc: stable@...r.kernel.org

 arch/arm/include/asm/uaccess.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index 12c3a5d..75d9579 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -171,8 +171,9 @@ extern int __put_user_8(void *, unsigned long long);
 #define __put_user_check(x,p)							\
 	({								\
 		unsigned long __limit = current_thread_info()->addr_limit - 1; \
+		const typeof(*(p)) __user *__tmp_p = (p);		\
 		register const typeof(*(p)) __r2 asm("r2") = (x);	\
-		register const typeof(*(p)) __user *__p asm("r0") = (p);\
+		register const typeof(*(p)) __user *__p asm("r0") = __tmp_p; \
 		register unsigned long __l asm("r1") = __limit;		\
 		register int __e asm("r0");				\
 		switch (sizeof(*(__p))) {				\
-- 
1.8.5.5

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