[PATCH] arm64: avoid multiple evaluation of ptr in get_user/put_user()

[AKASHI Takahiro]

get_user() is defined as a function macro in arm64, and trace_get_user()
calls it as followed:
     get_user(ch, ptr++);
Since the second parameter occurs twice in the definition, 'ptr++' is
unexpectedly evaluated twice and trace_get_user() will generate a bogus
string from user-provided one. As a result, some ftrace sysfs operations,
like "echo FUNCNAME > set_ftrace_filter," hit this case and eventually fail.
This patch fixes the issue both in get_user() and put_user().

Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
---
  arch/arm64/include/asm/uaccess.h |   12 ++++++++----
  1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index edb3d5c..bbeab83 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -166,9 +166,11 @@ do {									\
   #define get_user(x, ptr)						\
  ({									\
+	__typeof__(*(ptr)) *optr = (ptr);				\
+									\
  	might_fault();							\
-	access_ok(VERIFY_READ, (ptr), sizeof(*(ptr))) ?			\
-		__get_user((x), (ptr)) :				\
+	access_ok(VERIFY_READ, optr, sizeof(*optr)) ?			\
+		__get_user((x), optr) :					\
  		((x) = 0, -EFAULT);					\
  })
  @@ -227,9 +229,11 @@ do {									\
   #define put_user(x, ptr)						\
  ({									\
+	__typeof__(*(ptr)) *optr = (ptr);				\
+									\
  	might_fault();							\
-	access_ok(VERIFY_WRITE, (ptr), sizeof(*(ptr))) ?		\
-		__put_user((x), (ptr)) :				\
+	access_ok(VERIFY_WRITE, optr, sizeof(*optr)) ?			\
+		__put_user((x), optr) :					\
  		-EFAULT;						\
  })
  -- 1.7.9.5