linux-kernel - Re: [PATCH v4 2/3] x86/ldt: Make modify

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Message-ID: <20150725075052.GA3918@1wt.eu>
Date:	Sat, 25 Jul 2015 09:50:52 +0200
From:	Willy Tarreau <w@....eu>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"security@...nel.org" <security@...nel.org>,
	X86 ML <x86@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Sasha Levin <sasha.levin@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Jan Beulich <jbeulich@...e.com>,
	xen-devel <xen-devel@...ts.xen.org>
Subject: Re: [PATCH v4 2/3] x86/ldt: Make modify_ldt optional

On Fri, Jul 24, 2015 at 11:44:52PM -0700, Andy Lutomirski wrote:
> I'm all for it, but I think it should be hard-disablable in config,
> too, for the -tiny people.

I totally agree.

> If we add a runtime disable, let's do a
> separate patch, and you and Kees can fight over how general it should
> be.

Initially I was thinking about changing it for a 3-state option but
that would prevent X86_16BIT from being hard-disablable, so I'll do
something completely separate.

> > That's why here I think we should do the same, and possibly even
> > emit a warning once to report the first user of modify_ldt if that
> > can help.
> >
> > What do you think ?
> 
> I'm generally in favor.

OK.

> On the other hand, the current series is already written, might even
> be compatible with Xen, and patch 1 at least fixes a real bug.  Maybe
> several real bugs.

That's my guess as well given how hard it seems for everyone in this
long thread to imagine all possible bugs we can face :-/

Thanks,
Willy

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