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

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

From: Dan Williams <dan.j.willi...@intel.com>

commit 1d91c1d2c80cb70e2e553845e278b87a960c04da upstream.

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().

Reported-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Arjan van de Ven <ar...@linux.intel.com>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: David Woodhouse <dw...@infradead.org>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Josh Poimboeuf <jpoim...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Will Deacon <will.dea...@arm.com>
Cc: linux-a...@vger.kernel.org
Link: 
http://lkml.kernel.org/r/151881604278.17395.6605847763178076520.st...@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
 include/linux/nospec.h | 22 +---------------------
 1 file changed, 1 insertion(+), 21 deletions(-)

--- a/include/linux/nospec.h
+++ b/include/linux/nospec.h
@@ -30,26 +30,6 @@ 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:
@@ -67,7 +47,7 @@ static inline unsigned long array_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));                        \

Reply via email to