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Message-ID: <58df7ae3-8ef0-4f42-9ab2-b551d2ffff00@embeddedor.com>
Date: Sun, 20 May 2018 19:50:21 -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 05/18/2018 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); \
+})
#endif /* _LINUX_NOSPEC_H */
Thanks
--
Gustavo
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