lkml.org 
[lkml]   [2018]   [May]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] kernel: sys: fix potential Spectre v1
From
Date


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

\
 
 \ /
  Last update: 2018-05-21 04:01    [W:0.093 / U:12.504 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site