linux-kernel - Re: [patch 11/11] x66/vdso: Add CLOCK

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: <FAE37798-8CCE-44A5-9EF0-F69C2199BE60@amacapital.net>
Date:   Fri, 14 Sep 2018 07:59:42 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Matt Rickard <matt@...trans.com.au>,
        Stephen Boyd <sboyd@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        Florian Weimer <fweimer@...hat.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        devel@...uxdriverproject.org,
        virtualization@...ts.linux-foundation.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Juergen Gross <jgross@...e.com>
Subject: Re: [patch 11/11] x66/vdso: Add CLOCK_TAI support



> On Sep 14, 2018, at 7:27 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> On Fri, 14 Sep 2018, Andy Lutomirski wrote:
>>> On Sep 14, 2018, at 5:50 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
>>> 
>>> With the storage array in place it's now trivial to support CLOCK_TAI in
>>> the vdso. Instead of extending the array to accomodate CLOCK_TAI, make use
>>> of the fact that:
>>> 
>>> - CLOCK ids are set in stone
>>> - CLOCK_THREAD_CPUTIME is never going to be supported in the VDSO so
>>>  the array slot 3 is unused
>>> - CLOCK_TAI is id 11 which results in 3 when masked with 0x3
>>> 
>>> Add the mask to the basetime array lookup and set up the CLOCK_TAI base
>>> time in update_vsyscall().
>> 
>> That’s... horrible. In an amazing way. Can you add BUILD_BUG_ON somewhere
>> to assert that this actually works?
> 
> Sure, but changing any of the clock ids will cause more wreckage than that.
> 

I’m more concerned that we add a new one and break the magic masking. Maybe two start sharing the same slot. 

> Thanks,
> 
>    tglx