From: David Laight <David.Laight@ACULAB.COM>
To: 'Linus Torvalds' <torvalds@linux-foundation.org>,
Mikulas Patocka <mpatocka@redhat.com>
Cc: Andy Shevchenko <andy@kernel.org>,
device-mapper development <dm-devel@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
Herbert Xu <herbert@gondor.apana.org.au>,
"David S. Miller" <davem@davemloft.net>,
Mike Snitzer <msnitzer@redhat.com>,
Mimi Zohar <zohar@linux.ibm.com>,
Milan Broz <gmazyland@gmail.com>
Subject: RE: [PATCH] hex2bin: make the function hex_to_bin constant-time
Date: Mon, 25 Apr 2022 09:37:53 +0000 [thread overview]
Message-ID: <789f0463ce974e90a93f4dbf8c471156@AcuMS.aculab.com> (raw)
In-Reply-To: <CAHk-=wibmkFz6dybsdpW_3kUnV20FhJazerWDcbm7yCp_Xv+CA@mail.gmail.com>
From: Linus Torvalds
> Sent: 24 April 2022 22:42
>
> On Sun, Apr 24, 2022 at 2:37 PM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Finally, for the same reason - please don't use ">> 8". Because I do
> > not believe that bit 8 is well-defined in your arithmetic. The *sign*
> > bit will be, but I'm not convinced bit 8 is.
>
> Hmm.. I think it's ok. It can indeed overflow in 'char' and change the
> sign in bit #7, but I suspect bit #8 is always fine.
>
> Still, If you want to just extend the sign bit, ">> 31" _is_ the
> obvious thing to use (yeah, yeah, properly "sizeof(int)*8-1" or
> whatever, you get my drift).
Except that right shifts of signed values are UB.
In particular it has always been valid to do an unsigned
shift right on a 2's compliment negative number.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-04-25 9:40 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-24 20:54 [PATCH] hex2bin: make the function hex_to_bin constant-time Mikulas Patocka
2022-04-24 21:30 ` Joe Perches
2022-04-24 21:37 ` Linus Torvalds
2022-04-24 21:42 ` Linus Torvalds
2022-04-25 9:37 ` David Laight [this message]
2022-04-25 11:04 ` Mikulas Patocka
2022-04-25 12:59 ` David Laight
2022-04-25 13:33 ` Mikulas Patocka
2022-04-25 12:07 ` [PATCH v2] " Mikulas Patocka
2022-04-25 17:53 ` Linus Torvalds
2022-05-04 8:38 ` Stafford Horne
2022-05-04 8:57 ` Mikulas Patocka
2022-05-04 9:20 ` Andy Shevchenko
2022-05-04 9:47 ` Milan Broz
2022-05-04 9:50 ` Jason A. Donenfeld
2022-05-04 11:54 ` Mikulas Patocka
2022-05-04 9:42 ` Jason A. Donenfeld
2022-05-04 9:44 ` Jason A. Donenfeld
2022-05-04 9:57 ` Jason A. Donenfeld
2022-05-04 10:07 ` Andy Shevchenko
2022-05-04 10:15 ` Jason A. Donenfeld
2022-05-04 18:00 ` Linus Torvalds
2022-05-04 19:42 ` Jason A. Donenfeld
2022-05-04 19:51 ` Linus Torvalds
2022-05-04 20:00 ` Linus Torvalds
2022-05-04 20:12 ` Stafford Horne
2022-05-04 20:26 ` Linus Torvalds
2022-05-04 21:24 ` Linus Torvalds
2022-05-04 19:57 ` Stafford Horne
2022-05-04 20:10 ` Linus Torvalds
2022-05-04 20:38 ` Stafford Horne
2022-05-08 0:37 ` Stafford Horne
2022-05-11 12:17 ` Stafford Horne
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