Subject: [PATCH for-stable-v4.4 36/53] ARM: use __inttype() in get_user()

From: Ard Biesheuvel <[email-masked]>
Date: Tue, 5 Nov 2019 21:58:29 +0100

From: Russell King <[email-masked]>

Commit d09fbb327d670737ab40fd8bbb0765ae06b8b739 upstream.

Borrow the x86 implementation of __inttype() to use in get_user() to
select an integer type suitable to temporarily hold the result value.
This is necessary to avoid propagating the volatile nature of the
result argument, which can cause the following warning:

lib/iov_iter.c:413:5: warning: optimization may eliminate reads and/or writes to register variables [-Wvolatile-register-var]

Acked-by: Mark Rutland <[email-masked]>
Signed-off-by: Russell King <[email-masked]>
Signed-off-by: David A. Long <[email-masked]>
Signed-off-by: Greg Kroah-Hartman <[email-masked]>
Signed-off-by: Ard Biesheuvel <[email-masked]>
---
 arch/arm/include/asm/uaccess.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index b0f9269bef1c..99005567fb92 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -122,6 +122,13 @@ static inline void set_fs(mm_segment_t fs)
 		: "cc"); \
 	flag; })
 
+/*
+ * This is a type: either unsigned long, if the argument fits into
+ * that type, or otherwise unsigned long long.
+ */
+#define __inttype(x) \
+	__typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
+
 /*
  * Single-value transfer routines.  They automatically use the right
  * size if we just have the right pointer type.  Note that the functions
@@ -191,7 +198,7 @@ extern int __get_user_64t_4(void *);
 	({								\
 		unsigned long __limit = current_thread_info()->addr_limit - 1; \
 		register const typeof(*(p)) __user *__p asm("r0") = (p);\
-		register typeof(x) __r2 asm("r2");			\
+		register __inttype(x) __r2 asm("r2");			\
 		register unsigned long __l asm("r1") = __limit;		\
 		register int __e asm("r0");				\
 		unsigned int __ua_flags = uaccess_save_and_enable();	\
-- 
2.17.1

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