linux-kernel - Re: [PATCH 1/3] futex: remove duplicated code

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <3994975e-89a5-d2b5-60be-a8633ddc3733@zytor.com>
Date:   Sat, 4 Mar 2017 11:15:17 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Jiri Slaby <jslaby@...e.cz>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Vineet Gupta <vgupta@...opsys.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Richard Kuo <rkuo@...eaurora.org>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Michal Simek <monstr@...str.eu>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        Arnd Bergmann <arnd@...db.de>, x86@...nel.org,
        linux-alpha@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-mips@...ux-mips.org, openrisc@...ts.librecores.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/3] futex: remove duplicated code

On 03/04/17 05:05, Russell King - ARM Linux wrote:
>>  
>> +static int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
>> +{
>> +	int op = (encoded_op >> 28) & 7;
>> +	int cmp = (encoded_op >> 24) & 15;
>> +	int oparg = (encoded_op << 8) >> 20;
>> +	int cmparg = (encoded_op << 20) >> 20;
> 
> Hmm.  oparg and cmparg look like they're doing these shifts to get sign
> extension of the 12-bit values by assuming that "int" is 32-bit -
> probably worth a comment, or for safety, they should be "s32" so it's
> not dependent on the bit-width of "int".
> 

For readability, perhaps we should make sign- and zero-extension an
explicit facility?

/*
 * Truncate an integer x to n bits, using sign- or
 * zero-extension, respectively.
 */
static inline __const_func__ s32 sex32(s32 x, int n)
{
  return (x << (32-n)) >> (32-n);
}

static inline __const_func__ s64 sex64(s64 x, int n)
{
  return (x << (64-n)) >> (64-n);
}

#define sex(x,y)						\
	((__typeof__(x))					\
	 (((__builtin_constant_p(y) && ((y) <= 32)) ||		\
	   (sizeof(x) <= sizeof(s32)))				\
	  ? sex32((x),(y)) : sex64((x),(y))))

static inline __const_func__ u32 zex32(u32 x, int n)
{
  return (x << (32-n)) >> (32-n);
}

static inline __const_func__ u64 zex64(u64 x, int n)
{
  return (x << (64-n)) >> (64-n);
}

#define zex(x,y)						\
	((__typeof__(x))					\
	 (((__builtin_constant_p(y) && ((y) <= 32)) ||		\
	   (sizeof(x) <= sizeof(u32)))				\
	  ? zex32((x),(y)) : zex64((x),(y))))