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SubjectRe: [PATCH] kernel: sys: fix potential Spectre v1
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On 05/22/2018 03:50 PM, Dan Williams wrote:
>>>
>>> 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);
>>
>
> Let's not use ternary conditionals at all to make this more readable.
>

OK. How about this:

diff --git a/include/linux/nospec.h b/include/linux/nospec.h
index e791ebc..498995b 100644
--- a/include/linux/nospec.h
+++ b/include/linux/nospec.h
@@ -55,4 +55,21 @@ static inline unsigned long
array_index_mask_nospec(unsigned long index,
\
(typeof(_i)) (_i & _mask); \
})
+
+#define validate_index_nospec(index, size) \
+({ \
+ bool ret = true; \
+ typeof(index) *ptr = &(index); \
+ typeof(size) _s = (size); \
+ \
+ BUILD_BUG_ON(sizeof(*ptr) > sizeof(long)); \
+ BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
+ \
+ if (*ptr >= size) \
+ ret = false; \
+ \
+ *ptr = array_index_nospec(*ptr, _s); \
+ \
+ ret; \
+})
#endif /* _LINUX_NOSPEC_H */
Thanks
--
Gustavo

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