[PATCH 3.2 098/104] nospec: Move array_index_nospec() parameter checking into separate macro

[Ben Hutchings]

3.2.101-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Will Deacon <will.deacon@xxxxxxx>

commit 8fa80c503b484ddc1abbd10c7cb2ab81f3824a50 upstream.

For architectures providing their own implementation of
array_index_mask_nospec() in asm/barrier.h, attempting to use WARN_ONCE() to
complain about out-of-range parameters using WARN_ON() results in a mess
of mutually-dependent include files.

Rather than unpick the dependencies, simply have the core code in nospec.h
perform the checking for us.

Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1517840166-15399-1-git-send-email-will.deacon@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 include/linux/nospec.h | 36 +++++++++++++++++++++---------------
 1 file changed, 21 insertions(+), 15 deletions(-)

--- a/include/linux/nospec.h
+++ b/include/linux/nospec.h
@@ -20,20 +20,6 @@ static inline unsigned long array_index_
 						    unsigned long size)
 {
 	/*
-	 * Warn developers about inappropriate array_index_nospec() usage.
-	 *
-	 * Even if the CPU speculates past the WARN_ONCE branch, the
-	 * sign bit of @index is taken into account when generating the
-	 * mask.
-	 *
-	 * This warning is compiled out when the compiler can infer that
-	 * @index and @size are less than LONG_MAX.
-	 */
-	if (WARN_ONCE(index > LONG_MAX || size > LONG_MAX,
-			"array_index_nospec() limited to range of [0, LONG_MAX]\n"))
-		return 0;
-
-	/*
 	 * Always calculate and emit the mask even if the compiler
 	 * thinks the mask is not needed. The compiler does not take
 	 * into account the value of @index under speculation.
@@ -44,6 +30,26 @@ static inline unsigned long array_index_
 #endif
 
 /*
+ * Warn developers about inappropriate array_index_nospec() usage.
+ *
+ * Even if the CPU speculates past the WARN_ONCE branch, the
+ * sign bit of @index is taken into account when generating the
+ * mask.
+ *
+ * This warning is compiled out when the compiler can infer that
+ * @index and @size are less than LONG_MAX.
+ */
+#define array_index_mask_nospec_check(index, size)				\
+({										\
+	if (WARN_ONCE(index > LONG_MAX || size > LONG_MAX,			\
+	    "array_index_nospec() limited to range of [0, LONG_MAX]\n"))	\
+		_mask = 0;							\
+	else									\
+		_mask = array_index_mask_nospec(index, size);			\
+	_mask;									\
+})
+
+/*
  * array_index_nospec - sanitize an array index after a bounds check
  *
  * For a code sequence like:
@@ -61,7 +67,7 @@ static inline unsigned long array_index_
 ({									\
 	typeof(index) _i = (index);					\
 	typeof(size) _s = (size);					\
-	unsigned long _mask = array_index_mask_nospec(_i, _s);		\
+	unsigned long _mask = array_index_mask_nospec_check(_i, _s);	\
 									\
 	BUILD_BUG_ON(sizeof(_i) > sizeof(long));			\
 	BUILD_BUG_ON(sizeof(_s) > sizeof(long));			\