From: Kees Cook <keescook@chromium.org>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Leon Romanovsky <leon@kernel.org>,
Doug Ledford <dledford@redhat.com>,
Leon Romanovsky <leonro@mellanox.com>,
RDMA mailing list <linux-rdma@vger.kernel.org>,
Hadar Hen Zion <hadarh@mellanox.com>,
Matan Barak <matanb@mellanox.com>,
Michael J Ruhl <michael.j.ruhl@intel.com>,
Noa Osherovich <noaos@mellanox.com>,
Raed Salem <raeds@mellanox.com>,
Yishai Hadas <yishaih@mellanox.com>,
Saeed Mahameed <saeedm@mellanox.com>,
linux-netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH rdma-next 08/12] overflow.h: Add arithmetic shift helper
Date: Wed, 27 Jun 2018 11:44:23 -0700 [thread overview]
Message-ID: <CAGXu5jL-_o0mQGzWoOg5VHj0sUfrkDH-yrOg0A3BxQRe+VRmDw@mail.gmail.com> (raw)
In-Reply-To: <20180627181012.GM20754@mellanox.com>
On Wed, Jun 27, 2018 at 11:10 AM, Jason Gunthorpe <jgg@mellanox.com> wrote:
> Leon? Seems like agreement, Can you work with this version?
>
> #include <stdint.h>
> #include <stdbool.h>
> #include <assert.h>
>
> #define u64 uint64_t
>
> /*
> * Compute *d = (a << s)
> *
> * Returns true if '*d' cannot hold the result or 'a << s' doesn't make sense.
> * - 'a << s' causes bits to be lost when stored in d
> * - 's' is garbage (eg negative) or so large that a << s is guarenteed to be 0
> * - 'a' is negative
> * - 'a << s' sets the sign bit, if any, in '*d'
> * *d is not defined if false is returned.
> */
> #define check_shift_overflow(a, s, d) \
> ({ \
> typeof(a) _a = a; \
> typeof(s) _s = s; \
> typeof(d) _d = d; \
> u64 _a_full = _a; \
> unsigned int _to_shift = \
> _s >= 0 && _s < 8 * sizeof(*d) ? _s : 0; \
> \
> *_d = (_a_full << _to_shift); \
> \
> (_to_shift != _s || *_d < 0 || _a < 0 || \
> (*_d >> _to_shift) != a); \
> })
>
> int main(int argc, const char *argv[])
> {
> int32_t s32;
> uint32_t u32;
>
> assert(check_shift_overflow(1, 0, &s32) == false && s32 == (1 << 0));
> assert(check_shift_overflow(1, 1, &s32) == false && s32 == (1 << 1));
> assert(check_shift_overflow(1, 30, &s32) == false && s32 == (1 << 30));
> assert(check_shift_overflow(1, 31, &s32) == true);
> assert(check_shift_overflow(1, 32, &s32) == true);
> assert(check_shift_overflow(-1, 1, &s32) == true);
> assert(check_shift_overflow(-1, 0, &s32) == true);
>
> assert(check_shift_overflow(1, 0, &u32) == false && u32 == (1 << 0));
> assert(check_shift_overflow(1, 1, &u32) == false && u32 == (1 << 1));
> assert(check_shift_overflow(1, 30, &u32) == false && u32 == (1 << 30));
> assert(check_shift_overflow(1, 31, &u32) == false && u32 == (1UL << 31));
> assert(check_shift_overflow(1, 32, &u32) == true);
> assert(check_shift_overflow(-1, 1, &u32) == true);
> assert(check_shift_overflow(-1, 0, &u32) == true);
>
> assert(check_shift_overflow(0xFFFFFFFF, 0, &u32) == false && u32 == (0xFFFFFFFFUL << 0));
> assert(check_shift_overflow(0xFFFFFFFF, 1, &u32) == true);
> assert(check_shift_overflow(0xFFFFFFFF, 0, &s32) == true);
> assert(check_shift_overflow(0xFFFFFFFF, 1, &s32) == true);
> }
Oh yes, please include these tests in lib/test_overflow.c too! Nice. :)
-Kees
--
Kees Cook
Pixel Security
next prev parent reply other threads:[~2018-06-27 18:44 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20180624082353.16138-1-leon@kernel.org>
2018-06-24 8:23 ` [PATCH rdma-next 08/12] overflow.h: Add arithmetic shift helper Leon Romanovsky
[not found] ` <CAKwiHFhgsyWYD+q+JFb2HJEphnjiiOp=o4Airv3MW031q2jx8w@mail.gmail.com>
2018-06-25 17:11 ` Jason Gunthorpe
2018-06-26 4:16 ` Leon Romanovsky
[not found] ` <CAKwiHFiRYbyiJqDYCgKXKZYRr0KjCt8q9AwKwfqoCA1sT2KFyQ@mail.gmail.com>
2018-06-26 11:37 ` Leon Romanovsky
2018-06-26 17:54 ` Jason Gunthorpe
[not found] ` <CAKwiHFgchr+6HYOZ4e4e1vzL9cFabe6eonNNM8NTWZypazcuKA@mail.gmail.com>
2018-06-27 17:39 ` Leon Romanovsky
2018-06-27 18:10 ` Jason Gunthorpe
2018-06-27 18:22 ` Leon Romanovsky
2018-06-27 21:35 ` Rasmus Villemoes
2018-06-27 18:44 ` Kees Cook [this message]
2018-08-01 9:36 ` Peter Zijlstra
2018-08-01 16:14 ` Jason Gunthorpe
2018-06-26 4:24 ` Leon Romanovsky
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