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From: Andy Lutomirski <luto@amacapital.net>
Date: Tue, 28 Jul 2015 10:07:01 -0700
Message-ID: <CALCETrVd56uwkZw0YtaSHKHp5dh7NugQouigibJkr=e3Q_mYyA@mail.gmail.com>
Subject: Re: [PATCH v4 0/3] x86: modify_ldt improvement, test, and config option
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "security@kernel.org" <security@kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Borislav Petkov <bp@alien8.de>, X86 ML <x86@kernel.org>,
        xen-devel <xen-devel@lists.xen.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Jan Beulich <jbeulich@suse.com>, Sasha Levin <sasha.levin@oracle.com>,
        Peter Zijlstra <peterz@infradead.org>
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On Tue, Jul 28, 2015 at 9:30 AM, Andrew Cooper
<andrew.cooper3@citrix.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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