linux-kernel - Re: [PATCH v4 0/3] x86: modify_ldt improvement, test, and config option

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Date:	Tue, 28 Jul 2015 10:07:01 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Andrew Cooper <andrew.cooper3@...rix.com>
Cc:	"security@...nel.org" <security@...nel.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...en8.de>, X86 ML <x86@...nel.org>,
	xen-devel <xen-devel@...ts.xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jan Beulich <jbeulich@...e.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v4 0/3] x86: modify_ldt improvement, test, and config option

On Tue, Jul 28, 2015 at 9:30 AM, Andrew Cooper
<andrew.cooper3@...rix.com> wrote:
> I suspect that the set_ldt(NULL, 0) call hasn't reached Xen before
> xen_free_ldt() is attempting to nab back the pages which Xen still has
> mapped as an LDT.
>

I just instrumented it with yet more LSL instructions.  I'm pretty
sure that set_ldt really is clearing at least LDT entry zero.
Nonetheless the free_ldt call still oopses.

--Andy

> ~Andrew



-- 
Andy Lutomirski
AMA Capital Management, LLC
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