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Message-ID: <161a0513-1029-a76c-f967-1e606081599d@embeddedor.com>
Date: Sun, 20 May 2018 21:00:26 -0500
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Dan Williams <dan.j.williams@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Alexei Starovoitov <ast@...nel.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] kernel: sys: fix potential Spectre v1
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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