[tip:x86/asm] x86/uaccess: Fix implicit cast of __user pointer

[tip-bot for Jann Horn <tipbot@zytor.com>]

Commit-ID:  a6cbfbe6677efb5ca47bb7958c2718236c25126e
Gitweb:     https://git.kernel.org/tip/a6cbfbe6677efb5ca47bb7958c2718236c25126e
Author:     Jann Horn <jannh@google.com>
AuthorDate: Fri, 29 Mar 2019 22:46:52 +0100
Committer:  Borislav Petkov <bp@suse.de>
CommitDate: Wed, 3 Apr 2019 16:26:17 +0200

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.

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Qiaowei Ren <qiaowei.ren@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190329214652.258477-4-jannh@google.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;								\
 })