There are multiple problems with the dynamic sanity checking in
array_index_nospec_mask_check():
* It causes unnecessary overhead in the 32-bit case since integer sized
@index values will no longer cause the check to be compiled away like
in the 64-bit case.
* In the 32-bit case it may trigger with user controllable input when
the expectation is that should only trigger during development of new
kernel enabling.
* The macro reuses the input parameter in multiple locations which is
broken if someone passes an expression like 'index++' to
array_index_nospec().
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Dan Williams <dan.j.willi...@intel.com>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Will Deacon <will.dea...@arm.com>
Reported-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
---
include/linux/nospec.h | 22 +---------------------
1 file changed, 1 insertion(+), 21 deletions(-)
diff --git a/include/linux/nospec.h b/include/linux/nospec.h
index fbc98e2c8228..d6701e34424f 100644
--- a/include/linux/nospec.h
+++ b/include/linux/nospec.h
@@ -30,26 +30,6 @@ 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:
@@ -67,7 +47,7 @@ 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_check(_i, _s); \
+ unsigned long _mask = array_index_mask_nospec(_i, _s); \
\
BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
