nospec: Move array_index_nospec() parameter checking into separate macro

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@arm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1517840166-15399-1-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 21 insertions, 15 deletions

diff --git a/include/linux/nospec.h b/include/linux/nospec.h
index b99bced39ac2..fbc98e2c8228 100644
--- a/include/linux/nospec.h
+++ b/include/linux/nospec.h
@@ -20,20 +20,6 @@ static inline unsigned long array_index_mask_nospec(unsigned long 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_mask_nospec(unsigned long 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_mask_nospec(unsigned long 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));                        \