linux-kernel - Re: Assignment of GDT entries

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: <200609140800.13735.ak@suse.de>
Date:	Thu, 14 Sep 2006 08:00:13 +0200
From:	Andi Kleen <ak@...e.de>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Linus Torvalds <torvalds@...l.org>, Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Zachary Amsden <zach@...are.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Michael A Fetterman <Michael.Fetterman@...cam.ac.uk>
Subject: Re: Assignment of GDT entries

On Wednesday 13 September 2006 20:58, Jeremy Fitzhardinge wrote:
> What's the rationale for the current assignment of GDT entries?  In
> particular, this section:

AFAIK it was mostly for APM and various BIOS bugs.  IIRC Wine had 
some special requirements at some point too, but I can't remember them right
now. On x86-64 I use all GDT entries, although there are a few special 
ordering restrictions due to the semantics of SYSCALL. I ignored Wine too and 
so far nobody has complained, so whatever requirements they have they can't 
be that important.

> I'm asking because I'd like to use one of these entries for the PDA
> descriptor, so that it is on the same cache line as the TLS
> descriptors.  That way, the entry/exit segment register reloads would
> still only need to touch two GDT cache lines.  Would there be a real
> problem in doing this?

The only way to find out would be to do it. It's quite possible that all 
the systems with APM BIOS that needed it are long beyond their MTBF.

-Andi
-
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/