linux-kernel - Re: [tip:core/rseq] rseq/selftests/x86: Work around bogus gcc-8 optimisation

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] [day] [month] [year] [list]

Message-ID: <1655257247.250.1555727289505.JavaMail.zimbra@efficios.com>
Date:   Fri, 19 Apr 2019 22:28:09 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Chris Lameter <cl@...ux.com>, shuah <shuah@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Dave Watson <davejwatson@...com>,
        Boqun Feng <boqun.feng@...il.com>,
        Russell King <linux@....linux.org.uk>,
        Paul Turner <pjt@...gle.com>, Ben Maurer <bmaurer@...com>,
        Joel Fernandes <joelaf@...gle.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        rostedt <rostedt@...dmis.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-tip-commits <linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:core/rseq] rseq/selftests/x86: Work around bogus gcc-8
 optimisation

----- On Apr 19, 2019, at 5:13 PM, Mathieu Desnoyers mathieu.desnoyers@...icios.com wrote:

> ----- On Apr 19, 2019, at 2:53 PM, Linus Torvalds torvalds@...ux-foundation.org
> wrote:
> 
>> On Fri, Apr 19, 2019 at 11:46 AM tip-bot for Mathieu Desnoyers
>> <tipbot@...or.com> wrote:
>>>
>>> rseq/selftests/x86: Work around bogus gcc-8 optimisation
>>>
>>> At least the following versions of gcc-8:
>>>
>>>  - gcc version 8.0.1 20180414 (experimental) [trunk revision 259383] (Ubuntu
>>>  8-20180414-1ubuntu2)
>>>  - gcc 8.2.0-7ubuntu1 (Ubuntu 18.10 (Cosmic)),
>>>
>>> generate broken assembler with asm goto that have a thread-local storage
>>> "m" input operand on both x86-32 and x86-64. For instance:
>> 
>> Is there a gcc bugzilla for this? Shouldn't that be mentioned here?
> 
> My google-fu did not find any match, so I don't think so. I'll open one
> shortly.
> 
>> 
>> Also, we use "asm goto" together with "m" all the time in the kernel.
>> In fact, it's the most common case, with the RMWcc ops being generated
>> with that. I realize that we don't use the gcc thread-local storage
>> for them (we often do use our *own* thread-local storage), but it
>> would be good to have that gcc bugzilla to see why it can only affect
>> those user level "__thread" cases.
> 
> Indeed, it would be good to investigate and understand all problematic
> scenarios triggering this bug.

I've opened a ticket on gcc's bugzilla:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90193

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com