linux-kernel - Re: [RFC PATCH 2/4] rseq: Allow extending struct rseq

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: <1818805836.14259.1594823902146.JavaMail.zimbra@efficios.com>
Date:   Wed, 15 Jul 2020 10:38:22 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Florian Weimer <fw@...eb.enyo.de>
Cc:     Chris Kennelly <ckennelly@...gle.com>,
        Peter Oskolkov <posk@...gle.com>,
        Peter Oskolkov <posk@...k.io>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        paulmck <paulmck@...ux.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "H. Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api <linux-api@...r.kernel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        carlos <carlos@...hat.com>
Subject: Re: [RFC PATCH 2/4] rseq: Allow extending struct rseq

----- On Jul 15, 2020, at 2:31 AM, Florian Weimer fw@...eb.enyo.de wrote:

> * Chris Kennelly:
> 
>> When glibc provides registration, is the anticipated use case that a
>> library would unregister and reregister each thread to "upgrade" it to
>> the most modern version of interface it knows about provided by the
>> kernel?
> 
> Absolutely not, that is likely to break other consumers because an
> expected rseq area becomes dormant instead.

Indeed.

> 
>> There, I could assume an all-or-nothing registration of the new
>> feature--limited only by kernel availability for thread
>> homogeneity--but inconsistencies across early adopter libraries would
>> mean each thread would have to examine its own TLS to determine if a
>> feature were available.
> 
> Exactly.  Certain uses of seccomp can also have this effect,
> presenting a non-homogeneous view.

The nice thing about having a consistent feature-set for a given
thread group is that it allows specializing the code at thread
group startup, rather than requiring to dynamically check for
feature availability at runtime in fast-paths.

I wonder whether this kind of non-homogeneous view scenario
caused by seccomp is something we should support, or something
that should be documented as incompatible with rseq ?

Thanks,

Mathieu



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