linux-kernel - Re: [patch 5/8] Immediate Values

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: <20071115040610.GA23443@Krystal>
Date:	Wed, 14 Nov 2007 23:06:10 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@....de>, "H. Peter Anvin" <hpa@...or.com>,
	Chuck Ebbert <cebbert@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 5/8] Immediate Values - x86 Optimization

* Rusty Russell (rusty@...tcorp.com.au) wrote:
> On Wednesday 14 November 2007 05:58:05 Mathieu Desnoyers wrote:
> > x86 optimization of the immediate values which uses a movl with code
> > patching to set/unset the value used to populate the register used as
> > variable source.
> 
> For the record, I think the patching code gross overkill.
> 
> A stop_machine (or lightweight variant using IPI) would be sufficient and 
> vastly simpler.  Trying to patch NMI handlers while they're running is 
> already crazy.
> 

I wouldn't mind if it was limited to the code within do_nmi(), but then
we would have to accept potential GPF if

A - the NMI or MCE code calls any external kernel code (printk,
  notify_die, spin_lock/unlock, die_nmi, lapic_wd_event (perfctr code,
  calls printk too for debugging)...

B - we try to patch this code at the wrong moment

I could live with that, but I would prefer to have a solid, non flaky
solution. My goal is to help the kernel quality _improve_ rather than
deteriorate. Therefore, if one decides to use the immediate values to
leave dormant spinlock instrumentation in the kernel, I wouldn't want it
to have undesirable side-effects (GPF) when the instrumentation is
being enabled, as rare as it could be.

> I'd keep this version up your sleeve for they day when it's needed.
> 

If we choose to go this way, stop_machine would have to do a sync_core()
on every CPU before it reactivates interrupts for this to respect
Intel's errata. It's not just a matter of not executing the code while
it is modified; the issue here is that we must insure that we don't have
an incoherent trace cache.  So, as is, stop_machine would not respect
the errata.

Mathieu

> Rusty.

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/