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SubjectRe: [PATCH] kernel: sys: fix potential Spectre v1
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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); \
+})
#endif /* _LINUX_NOSPEC_H */
Thanks
--
Gustavo

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