From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] kernel: sys: fix potential Spectre v1
Date: Sun, 20 May 2018 21:00:26 -0500 [thread overview]
Message-ID: <161a0513-1029-a76c-f967-1e606081599d@embeddedor.com> (raw)
In-Reply-To: <58df7ae3-8ef0-4f42-9ab2-b551d2ffff00@embeddedor.com>
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
next prev parent reply other threads:[~2018-05-21 2:00 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-15 3:00 [PATCH] kernel: sys: fix potential Spectre v1 Gustavo A. R. Silva
2018-05-15 22:08 ` Andrew Morton
2018-05-15 22:29 ` Thomas Gleixner
2018-05-15 22:57 ` Dan Williams
2018-05-18 19:04 ` Gustavo A. R. Silva
2018-05-18 19:21 ` Gustavo A. R. Silva
2018-05-18 20:38 ` Dan Williams
2018-05-18 20:44 ` Gustavo A. R. Silva
2018-05-18 21:27 ` Gustavo A. R. Silva
2018-05-18 21:45 ` Dan Williams
2018-05-18 22:01 ` Gustavo A. R. Silva
2018-05-18 22:08 ` Dan Williams
2018-05-18 22:11 ` Gustavo A. R. Silva
2018-05-21 0:50 ` Gustavo A. R. Silva
2018-05-21 2:00 ` Gustavo A. R. Silva [this message]
2018-05-22 20:50 ` Dan Williams
2018-05-23 5:03 ` Gustavo A. R. Silva
2018-05-23 5:15 ` Dan Williams
2018-05-23 5:22 ` Gustavo A. R. Silva
2018-05-23 9:08 ` Peter Zijlstra
2018-05-23 13:55 ` Dan Williams
2018-05-23 15:07 ` Mark Rutland
2018-05-23 15:57 ` Dan Williams
2018-05-23 16:27 ` Peter Zijlstra
2018-05-23 16:31 ` Mark Rutland
2018-05-25 18:11 ` Gustavo A. R. Silva
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