From: Vadim Pasternak <vadimp@mellanox.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "jacek.anaszewski@gmail.com" <jacek.anaszewski@gmail.com>,
"pavel@ucw.cz" <pavel@ucw.cz>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-leds@vger.kernel.org" <linux-leds@vger.kernel.org>,
Ido Schimmel <idosch@mellanox.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>
Subject: RE: [PATCH v1 bitops] bitops: Fix UBSAN undefined behavior warning for rotation right
Date: Tue, 9 Apr 2019 07:36:06 +0000 [thread overview]
Message-ID: <AM6PR05MB52246C74B34F291F5D89A409A22D0@AM6PR05MB5224.eurprd05.prod.outlook.com> (raw)
In-Reply-To: <20190408155217.3f723554ae7fbcb34eeacb30@linux-foundation.org>
> -----Original Message-----
> From: Andrew Morton <akpm@linux-foundation.org>
> Sent: Tuesday, April 09, 2019 1:52 AM
> To: Vadim Pasternak <vadimp@mellanox.com>
> Cc: jacek.anaszewski@gmail.com; pavel@ucw.cz; linux-kernel@vger.kernel.org;
> linux-leds@vger.kernel.org; Ido Schimmel <idosch@mellanox.com>; Andrey
> Ryabinin <aryabinin@virtuozzo.com>
> Subject: Re: [PATCH v1 bitops] bitops: Fix UBSAN undefined behavior warning
> for rotation right
>
> (resend, cc Andrey)
>
> On Sun, 7 Apr 2019 12:53:25 +0000 Vadim Pasternak <vadimp@mellanox.com>
> wrote:
>
> > The warning is caused by call to rorXX(), if the second parameters of
> > this function "shift" is zero. In such case UBSAN reports the warning
> > for the next expression: (word << (XX - shift), where XX is 64, 32,
> > 16, 8 for respectively ror64, ror32, ror16, ror8.
> > Fix adds validation of this parameter - in case it's equal zero, no
> > need to rotate, just original "word" is to be returned to caller.
> >
> > The UBSAN undefined behavior warning has been reported for call to
> > ror32():
> > [ 11.426543] UBSAN: Undefined behaviour in ./include/linux/bitops.h:93:33
> > [ 11.434045] shift exponent 32 is too large for 32-bit type 'unsigned int'
>
> hm, do we care?
Hi Andrew,
Thank for reply.
We want to avoid UBSAN undefined behavior warning in case
"shift" parameter is not provided as a constant.
>
> > ...
> >
>
> > --- a/include/linux/bitops.h
> > +++ b/include/linux/bitops.h
> > @@ -70,6 +70,9 @@ static inline __u64 rol64(__u64 word, unsigned int shift)
> > */
> > static inline __u64 ror64(__u64 word, unsigned int shift) {
> > + if (!shift)
> > + return word;
> > +
> > return (word >> shift) | (word << (64 - shift)); }
>
> Is there any known architecture or compiler for which UL<<64 doesn't reliably
> produce zero? Is there any prospect that this will become a problem in the
> future?
I don't know about such architecture.
Do you think it could be modified only for ro8, ror16, ror32?
next prev parent reply other threads:[~2019-04-09 7:36 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-07 12:53 [PATCH v1 bitops] bitops: Fix UBSAN undefined behavior warning for rotation right Vadim Pasternak
2019-04-08 22:51 ` Andrew Morton
2019-04-08 22:52 ` Andrew Morton
2019-04-09 7:36 ` Vadim Pasternak [this message]
2019-04-09 8:08 ` Rasmus Villemoes
2019-04-09 8:57 ` Rasmus Villemoes
2019-04-09 9:50 ` Pavel Machek
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