linux-kernel - Re: [PATCH v3 1/3] overflow.h: Add arithmetic shift helper

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Message-ID: <CAGXu5jJ7yKsCdcKiqoXAoBPsQbWZK4ERMJnK5chdwJtQ+2AAag@mail.gmail.com>
Date:   Wed, 1 Aug 2018 11:44:22 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>,
        Bart Van Assche <Bart.VanAssche@....com>,
        Doug Ledford <dledford@...hat.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] overflow.h: Add arithmetic shift helper

On Wed, Aug 1, 2018 at 9:28 AM, Randy Dunlap <rdunlap@...radead.org> wrote:
> On 07/31/2018 11:09 PM, Kees Cook wrote:
>> From: Jason Gunthorpe <jgg@...lanox.com>
>>
>> Add shift_overflow() helper to assist driver authors in ensuring that
>> shift operations don't cause overflows or other odd conditions.
>>
>> Signed-off-by: Jason Gunthorpe <jgg@...lanox.com>
>> Signed-off-by: Leon Romanovsky <leonro@...lanox.com>
>> [kees: tweaked comments and commit log, dropped unneeded assignment]
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>  include/linux/overflow.h | 31 +++++++++++++++++++++++++++++++
>>  1 file changed, 31 insertions(+)
>>
>> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
>> index 8712ff70995f..69fc366ce865 100644
>> --- a/include/linux/overflow.h
>> +++ b/include/linux/overflow.h
>> @@ -202,6 +202,37 @@
>>
>>  #endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
>>
>> +/** check_shift_overflow() - Calculate a left-shifted value and check overflow
>> + *
>> + * @a: Value to be shifted
>> + * @b: How many bits left to shift
>> + * @d: Pointer to where to store the result
>> + *
>> + * Computes *@d = (@a << @s)
>> + *
>
> missed                     @b [again]

Heh, thanks. It's fixed on disk, but... I failed to merge it into the
patch. Anyway, I'll spin this one more time with s/shift/shl/ and this
fixed.

-Kees

-- 
Kees Cook
Pixel Security