linux-kernel - Re: [PATCH 0/9] posix_clocks: Prepare syscalls for 64 bit time

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: <CAK8P3a0wxs59T1zW4ahbJXeW6QjStm0mbCFoL_RQexAa6dzh_w@mail.gmail.com>
Date:   Fri, 17 Nov 2017 00:42:35 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Deepa Dinamani <deepa.kernel@...il.com>,
        John Stultz <john.stultz@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Chris Metcalf <cmetcalf@...lanox.com>, cohuck@...hat.com,
        David Miller <davem@...emloft.net>,
        Helge Deller <deller@....de>, devel@...verdev.osuosl.org,
        gerald.schaefer@...ibm.com, gregkh <gregkh@...uxfoundation.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Jan Hoeppner <hoeppner@...ux.vnet.ibm.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Julian Wiedmann <jwi@...ux.vnet.ibm.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:RALINK MIPS ARCHITECTURE" <linux-mips@...ux-mips.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        oberpar@...ux.vnet.ibm.com, oprofile-list@...ts.sf.net,
        Paul Mackerras <paulus@...ba.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Robert Richter <rric@...nel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        sebott@...ux.vnet.ibm.com, sparclinux <sparclinux@...r.kernel.org>,
        Stefan Haberland <sth@...ux.vnet.ibm.com>,
        Ursula Braun <ubraun@...ux.vnet.ibm.com>,
        Will Deacon <will.deacon@....com>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH 0/9] posix_clocks: Prepare syscalls for 64 bit time_t conversion

On Thu, Nov 16, 2017 at 10:04 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Wed, 15 Nov 2017, Deepa Dinamani wrote:
>> > I had on concern about x32, maybe we should check
>> > for "COMPAT_USE_64BIT_TIME" before zeroing out the tv_nsec
>> > bits.
>>
>> Thanks, I think you are right. I had the check conditional on
>> CONFIG_64BIT_TIME and then removed as I forgot why I added it. :)
>>
>> > Regarding CONFIG_COMPAT_TIME/CONFIG_64BIT_TIME, would
>> > it help to just leave out that part for now and unconditionally
>> > define '__kernel_timespec' as 'timespec' until we are ready to
>> > convert the architectures?
>>
>> Another approach would be to use separate configs:
>>
>> 1. To indicate 64 bit time_t syscall support. This will be dependent
>> on architectures as CONFIG_64BIT_TIME.
>> We can delete this once all architectures have provided support for this.
>>
>> 2. Another config (maybe COMPAT_32BIT_TIME?) to be introduced later,
>> which will compile out all syscalls/ features that use 32 bit time_t.
>> This can help build a y2038 safe kernel later.
>>
>> Would this work for everyone?
>
> Having extra config switches which are selectable by architectures and
> removed when everything is converted is definitely the right way to go.
>
> That allows you to gradually convert stuff w/o inflicting wreckage all over
> the place.

The CONFIG_64BIT_TIME would do that nicely for the new stuff like
the conditional definition of __kernel_timespec, this one would get
removed after we convert all architectures.

A second issue is how to control the compilation of the compat syscalls.
CONFIG_COMPAT_32BIT_TIME handles that and could be defined
in Kconfig as 'def_bool (!64BIT && CONFIG_64BIT_TIME) || COMPAT',
this is then just a more readable way of expressing exactly when the
functions should be built.

For completeness, there may be a third category, depending on how
we handle things like sys_nanosleep(): Here, we want the native
sys_nanosleep on 64-bit architectures, and compat_sys_nanosleep()
to handle the 32-bit time_t variant on both 32-bit and 64-bit targets,
but our plan is to not have a native 32-bit sys_nanosleep on 32-bit
architectures any more, as new glibc should call clock_nanosleep()
with a new syscall number instead. Should we then enclose
sys_nanosleep in "#if !defined(CONFIG_64BIT_TIME) ||
defined(CONFIG_64BIT)", or should we try to come up with another
Kconfig symbol name that expresses this better?

       Arnd