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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:
>>>>
>>>
>>> Oops, it seems I sent the wrong patch. The function would look like
>>> this:
>>>
>>> #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.
>
> Thanks for the feedback.

BTW, I'm analyzing other cases, like the following:

bool foo(int x)
{
if(!validate_index_nospec(&x))
return false;

[...]

return true;
}

int vulnerable(int x)
{
if (!foo(x))
return -1;

temp = array[x];

[...]

}

Basically my doubt is how deep this barrier can be placed into the call
chain in order to continue working.

Thanks
--
Gustavo

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