linux-kernel - [PATCH v3 4/4] x86/uaccess: Fix implicit cast of _

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Message-Id: <20190329214652.258477-4-jannh@google.com>
Date:   Fri, 29 Mar 2019 22:46:52 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, jannh@...gle.com
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Qiaowei Ren <qiaowei.ren@...el.com>,
        Mukesh Ojha <mojha@...eaurora.org>
Subject: [PATCH v3 4/4] x86/uaccess: Fix implicit cast of __user pointer

The first two arguments of __user_atomic_cmpxchg_inatomic() are:

 - `uval` is a kernel pointer into which the old value should be stored
 - `ptr` is the user pointer on which the cmpxchg should operate

This means that casting `uval` to `__typeof__(ptr)` is wrong. Since `uval`
is only used once inside the macro, just get rid of __uval and use `(uval)`
directly.

Reviewed-by: Mukesh Ojha <mojha@...eaurora.org>
Signed-off-by: Jann Horn <jannh@...gle.com>
---
 arch/x86/include/asm/uaccess.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 1954dd5552a2..a21f2a2f17bf 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -585,7 +585,6 @@ extern void __cmpxchg_wrong_size(void)
 #define __user_atomic_cmpxchg_inatomic(uval, ptr, old, new, size)	\
 ({									\
 	int __ret = 0;							\
-	__typeof__(ptr) __uval = (uval);				\
 	__typeof__(*(ptr)) __old = (old);				\
 	__typeof__(*(ptr)) __new = (new);				\
 	__uaccess_begin_nospec();					\
@@ -661,7 +660,7 @@ extern void __cmpxchg_wrong_size(void)
 		__cmpxchg_wrong_size();					\
 	}								\
 	__uaccess_end();						\
-	*__uval = __old;						\
+	*(uval) = __old;						\
 	__ret;								\
 })
 
-- 
2.21.0.392.gf8f6787159e-goog