On 05/20/2018 07:50 PM, Gustavo A. R. Silva wrote:


On 05/18/2018 03:44 PM, Gustavo A. R. Silva wrote:

#ifndef sanitize_index_nospec
inline bool sanitize_index_nospec(unsigned long *index,
                                   unsigned long size)
{
         if (*index >= size)
                 return false;
         *index = array_index_nospec(*index, size);

         return true;
}
#endif

I think this is fine in concept, we already do something similar in
mpls_label_ok(). Perhaps call it validate_index_nospec() since
validation is something that can fail, but sanitization in theory is
something that can always succeed.


OK. I got it.

However, the problem is the data type of the index. I expect you would
need to do this in a macro and use typeof() if you wanted this to be
generally useful, and also watch out for multiple usage of a macro
argument. Is it still worth it at that point?


Yeah. I think it is worth it. I'll work on this during the weekend and send a proper patch for review.


Dan,

What do you think about this first draft:

diff --git a/include/linux/nospec.h b/include/linux/nospec.h
index e791ebc..6154183 100644
--- a/include/linux/nospec.h
+++ b/include/linux/nospec.h
@@ -55,4 +55,16 @@ static inline unsigned long array_index_mask_nospec(unsigned long index,
                                                                        \
         (typeof(_i)) (_i & _mask);                                     \
  })
+
+#define validate_index_nospec(index, size)                            \
+({                                                                    \
+       typeof(index) *ptr = &(index);                                 \
+       typeof(size) _s = (size);                                      \
+                                                                      \
+       BUILD_BUG_ON(sizeof(*ptr) > sizeof(long));                     \
+       BUILD_BUG_ON(sizeof(_s) > sizeof(long));                       \
+                                                                      \
+       *ptr >= _s ? false :                                           \
+       (*ptr = array_index_nospec(*ptr, _s) ? true : true);           \

This actually should be:

((*ptr = array_index_nospec(*ptr, _s)) ? true : true);

+})
  #endif /* _LINUX_NOSPEC_H */

Thanks
--
Gustavo

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