Subject: [PATCH for-stable-v4.4 01/53] ARM: 8051/1: put_user: fix possible data corruption in put_user

From: Ard Biesheuvel <[email-masked]>
Date: Tue, 5 Nov 2019 21:57:54 +0100

From: Andrey Ryabinin <[email-masked]>

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 <[email-masked]>
Reviewed-by: Nicolas Pitre <[email-masked]>
Signed-off-by: Russell King <[email-masked]>
Signed-off-by: Ard Biesheuvel <[email-masked]>
---
 arch/arm/include/asm/uaccess.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index cd8b589111ba..35c9db857ebe 100644
--- 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 long long);
 	({								\
 		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");				\
-- 
2.17.1

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